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+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**K.101**
+
+(12/2014)
+
+SERIES K: PROTECTION AGAINST INTERFERENCE
+
+# --- Shielding factors for lightning protection
+
+Recommendation ITU-T K.101
+
+ITU-T
+
+![ITU logo: A globe with a red lightning bolt striking it, with the text 'ITU International Telecommunication Union' to the right.](84a1d09fb489061482111515543b60dc_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with a red lightning bolt striking it from the top right. To the right of the globe, the text "ITU" is written in a large, bold, blue font, and below it, "International Telecommunication Union" is written in a smaller, blue font.
+
+ITU logo: A globe with a red lightning bolt striking it, with the text 'ITU International Telecommunication Union' to the right.
+
+
+
+## Recommendation ITU-T K.101
+
+# Shielding factors for lightning protection
+
+## Summary
+
+Recommendation ITU-T K.101 contains the calculation procedure for the shielding factors used in Recommendations ITU-T K.46, ITU-T K.47, ITU-T K.56 and ITU-T K.97, and it is intended to:
+
+- 1) provide the rationale for the shielding factor approximate formulas or values contained in the aforementioned Recommendations;
+- 2) allow a more precise calculation of the shielding factors, by using the equations provided in this Recommendation.
+
+The shielding factors considered in this Recommendation refer to:
+
+- that of the lightning current distribution in a telecommunication tower, i.e., that of the tower ( $\alpha_T$ ) as per Recommendations ITU-T K.56 and ITU-T K.97;
+- that of the lightning current distribution among several conductors placed in a cable ladder, i.e., that of the feeder tray ( $\alpha_F$ ) as per Recommendations ITU-T K.56 and ITU-T K.97;
+- that provided by the cable tray ( $\beta$ ) as per Recommendation ITU-T K.56;
+- that of parallel conductors ( $\eta$ ) as per Recommendation ITU-T K.47;
+- that of refraction ( $\delta$ ) due to the earthing connection of a telecommunication cable, as per Recommendation ITU-T K.46;
+- that provided by a telecommunication cable having a metallic sheath (shield) ( $\eta$ ) as per Recommendation ITU-T K.46.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T K.101    | 2014-12-07 | 5           | <a href="http://handle.itu.int/11.1002/1000/12291">11.1002/1000/12291</a> |
+
+## Keywords
+
+Earthing, lightning, shielding, telecommunication lines, telecommunication towers.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2015
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                        | Page |
+|--------------------------------------------------------|------|
+| 1 Scope.....                                           | 1    |
+| 2 References.....                                      | 1    |
+| 3 Definitions .....                                    | 1    |
+| 3.1 Terms defined elsewhere .....                      | 1    |
+| 3.2 Terms defined in this Recommendation.....          | 2    |
+| 4 Abbreviations and acronyms .....                     | 2    |
+| 5 Conventions .....                                    | 2    |
+| 6 Shielding factor due to conductors in parallel ..... | 2    |
+| 6.1 Modelling the problem .....                        | 2    |
+| 6.2 Guard-wire.....                                    | 4    |
+| 6.3 Telecommunication towers .....                     | 4    |
+| 6.4 Cable trays and bundle of cables .....             | 7    |
+| 7 Earthing connection of cables.....                   | 8    |
+| 8 Shielding factor of telecommunication cables.....    | 10   |
+| Annex A – Geometric mean radius of conductors .....    | 11   |
+
+
+
+## Recommendation ITU-T K.101
+
+## Shielding factors for lightning protection
+
+## 1 Scope
+
+This Recommendation provides the rationale and formulas for calculating the shielding factors used in series K Recommendations dealing with lightning protection of telecommunication lines and structures. The shielding factors considered are related to:
+
+- the use of a metallic tower to hold telecommunication feeder cables and antennas;
+- the placement of several feeder cables in a metallic cable ladder in the tower;
+- the placement of telecommunication cables in a metallic cable tray;
+- the use of a guard-wire above a buried telecommunication cable;
+- the connection of a telecommunication cable to earth;
+- the use of a telecommunication cable with a metallic sheath.
+
+## 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T K.46] Recommendation ITU-T K.46 (2012), *Protection of telecommunication lines using metallic symmetric conductors against lightning-induced surges.*
+- [ITU-T K.47] Recommendation ITU-T K.47 (2012), *Protection of telecommunication lines against direct lightning flashes.*
+- [ITU-T K.56] Recommendation ITU-T K.56 (2010), *Protection of radio base stations against lightning discharges.*
+- [ITU-T K.97] Recommendation ITU-T K.97 (2014), *Lightning protection of distributed base stations.*
+
+## 3 Definitions
+
+### 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+- 3.1.1 cable tray** [ITU-T K.56]: Rigid structural system used to securely fasten or support cables.
+- 3.1.2 feeder cable** [ITU-T K.56]: Wave-guide or coaxial cable that conducts signals to an antenna.
+- 3.1.3 guard-wire** [ITU-T K.47]: Metallic wire buried above a cable in order to reduce physical damage due to direct lightning flashes to the cable.
+- 3.1.4 refraction factor** [ITU-T K.46]: Ratio between the common-mode surge voltage travelling in the line after passing through a discontinuity in its surge impedance and the surge that would travel in the line if there was no discontinuity in its surge impedance.
+
+**3.1.5 shielding factor** [ITU-T K.56]: Factor that represents the attenuation of the voltage or current in a conductor due to the presence of a nearby shielding conductor.
+
+### 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following terms:
+
+**3.2.1 shielded cable**: Group of one or more pairs of twisted wires balanced with respect to earth, assembled together and covered by a continuous metallic sheath.
+
+**3.2.2 unshielded cable**: Group of one or more pairs of twisted wires balanced with respect to earth and assembled together without a metallic sheath.
+
+## 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+DC Direct Current  
+GDT Gas Discharge Tube  
+GMR Geometric Mean Radius  
+SPC Surge Protective Component
+
+## 5 Conventions
+
+None.
+
+## 6 Shielding factor due to conductors in parallel
+
+The shielding factor, considered in this clause, is relevant to the following Recommendations:
+
+- [ITU-T K.56]:
+  - tower shielding factor ( $\alpha_T$ );
+  - feeder shielding factor ( $\alpha_F$ );
+  - shielding factors of cable trays ( $\beta$ ).
+- [ITU-T K.47]:
+  - guard-wire shielding factor ( $\eta$ ).
+
+## 6.1 Modelling the problem
+
+In many practical situations, there is a transient current injected in a transmission system formed by multiple conductors in parallel. This is the case of a metallic tower struck by lightning, where the current is distributed among the tower structure and the available conductors. As the time-derivative of the lightning current is high, the initial current distribution is determined by the magnetic flux linkages within the conductors. Therefore, if the low time-derivative wave-tail is not of concern, it is permissible to neglect the resistance of the conductors when assessing the current distribution.
+
+Under this assumption, a number of practical problems may be represented by the canonical structure shown in Figure 1, in which two perfectly conducting cylinders of radius  $r_1$  and  $r_2$  are placed in parallel and submitted to a time-varying current  $I(t)$ . The problem consists in determining the currents  $I_1(t)$  and  $I_2(t)$  of each conductor, based on their dimensions and separation  $b$ .
+
+The boundary condition required to calculate the current distribution is that the flux linkage in the area between the two conductors shall be null. This condition comes from the application of Maxwell's equation:
+
+$$\oint_L E \, dl = -\mu \oint_A \frac{dH}{dt} \, dA \quad (1)$$
+
+![Figure 1: A schematic diagram showing a transient current I(t) entering a system of two parallel conductors. The current splits into I1(t) flowing through an outer conductor and I2(t) flowing through an inner conductor. A dashed rectangular loop of length 'a' and height 'b' is shown, with its top and bottom segments inside the conductors. The distance from the top of the outer conductor to the top of the inner conductor is labeled r1, and the distance from the bottom of the inner conductor to the bottom of the outer conductor is labeled r2. Arrows indicate the direction of current flow: I(t) enters from the left, I1(t) flows to the right above the outer conductor, and I2(t) flows to the right below the inner conductor.](acfc53eca625d62b38aa2563efa95c3e_img.jpg)
+
+Figure 1: A schematic diagram showing a transient current I(t) entering a system of two parallel conductors. The current splits into I1(t) flowing through an outer conductor and I2(t) flowing through an inner conductor. A dashed rectangular loop of length 'a' and height 'b' is shown, with its top and bottom segments inside the conductors. The distance from the top of the outer conductor to the top of the inner conductor is labeled r1, and the distance from the bottom of the inner conductor to the bottom of the outer conductor is labeled r2. Arrows indicate the direction of current flow: I(t) enters from the left, I1(t) flows to the right above the outer conductor, and I2(t) flows to the right below the inner conductor.
+
+**Figure 1 – Representation of a transient current being split into two parallel conductors**
+
+where the integration of the electric field  $E$  follows the path  $L$  along the dashed line in Figure 1 and the magnetic field  $H$  is integrated in the area  $A = ab$  delineated by the dashed rectangle. As the electric field within a perfect conductor is null, the left-hand side of equation (1) is null. Therefore, the integral of the magnetic field time derivative within the loop area must be null.
+
+Consider that the magnetic field has an harmonic time dependency given by:
+
+$$H(t) = H_0 \exp(j\omega t) \quad (2)$$
+
+where  $\omega$  is the angular frequency and  $j = (-1)^{1/2}$  is the imaginary unit. This is not a limitation, as any impulsive signal can be broken down into a number of components of different frequencies. For each frequency, the integral of the magnetic field in the area between the conductors must be null. This means that the magnetic flux generated by the current  $I_1$  in the dashed loop must be equal to the magnetic flux generated by the current  $I_2$ , as the corresponding magnetic fields have opposite directions. This condition is expressed by:
+
+$$\int_{r_1}^{b-r_2} \frac{a I_1}{2\pi x} \, dx = \int_{r_2}^{b-r_1} \frac{a I_2}{2\pi x} \, dx \quad (3)$$
+
+Note that the integration limits are  $b - r_2$  and  $b - r_1$  because, due to the skin effect, the magnetic field within perfect conductors is null. A physical interpretation of equation (3) is that the smaller conductor 2 has a larger area to integrate the magnetic field, so that a lower current  $I_2$  is necessary to generate the same field that is generated by the current  $I_1$ . Solving equation (3) gives:
+
+$$I_1 \ln\left(\frac{b-r_2}{r_1}\right) = I_2 \ln\left(\frac{b-r_1}{r_2}\right) \quad (4)$$
+
+The total current is given by:
+
+$$I = I_1 + I_2 \quad (5)$$
+
+Defining the shielding factor ( $\eta$ ) as the fraction of the total current  $I$  that is left in conductor 1 after the placement of conductor 2, gives:
+
+$$\eta = I_1 / I \quad (6)$$
+
+Inserting equation (5) into equation (4) and rearranging gives:
+
+$$\eta = \ln\left(\frac{b - r_1}{r_2}\right) / \ln\left[\frac{(b - r_1)(b - r_2)}{r_1 r_2}\right] \quad (7)$$
+
+In the situations where  $b \gg r_1$  and  $b \gg r_2$ , equation (7) can be simplified as:
+
+$$\eta = \ln\left(\frac{b}{r_2}\right) / \ln\left(\frac{b^2}{r_1 r_2}\right) \quad (8)$$
+
+## 6.2 Guard-wire
+
+A common protection of buried cables against lightning flashes is the installation of a guard-wire above the cable, as shown in Figure 2. Besides protecting the cable from being directly struck by lightning (see [ITU-T K.47]), a guard-wire regularly bonded to the cable metallic sheath also diverts to earth part of the lightning current of the cable screen.
+
+The model described in clause 6.1 can be applied to this situation, as the two conductors are in parallel. Making reference to Figure 2, Equation (8) can be rewritten as:
+
+$$\eta = \ln\left(\frac{d}{r_g}\right) / \ln\left(\frac{d^2}{r_c r_g}\right) \quad (9)$$
+
+where  $r_g$  is the guard-wire radius,  $r_c$  is the telecommunication cable radius, and  $d$  is the distance between these conductors.
+
+For example, consider a guard-wire with radius  $r_g = 3$  mm placed in parallel with a buried cable with  $r_c = 10$  mm metallic sheath and bonded to it at regular intervals. The distance between the two conductors is  $d = 300$  mm. Equation (9) provides the shielding factor  $\eta = 0.58$ .
+
+If the cable of Figure 2 is connected to a structure (e.g., a telecommunication tower) that is struck by lightning, the cable metallic sheath will carry 58 per cent of the total current, while the guard-wire will carry the remaining 42 per cent. The reduction of the lightning current in the cable may have a significant effect on the cable protection, as described in [ITU-T K.47].
+
+![Diagram showing a guard-wire above a telecommunication cable. The guard-wire is a dark grey cylinder at the top, and the telecommunication cable is a light grey cylinder below it. The distance between their centers is labeled 'd'. The radius of the guard-wire is labeled 'r_g' and the radius of the telecommunication cable is labeled 'r_c'.](bd8e3fb102fd14e1edbc62f149241842_img.jpg)
+
+Diagram showing a guard-wire above a telecommunication cable. The guard-wire is a dark grey cylinder at the top, and the telecommunication cable is a light grey cylinder below it. The distance between their centers is labeled 'd'. The radius of the guard-wire is labeled 'r\_g' and the radius of the telecommunication cable is labeled 'r\_c'.
+
+**Figure 2 – Guard-wire above a telecommunication cable**
+
+## 6.3 Telecommunication towers
+
+The model developed in clause 6.2 may be used to assess the current distribution on towers struck by lightning. In this case, the relevant shielding factor is related to the fraction of the total lightning current that flows through the cable feeders. This clause shows some examples that are good approximations to common tower structures, where the shielding factor provided by the tower is designated  $\alpha_T$  to be in line with [ITU-T K.56] and [ITU-T K.97].
+
+#### 6.3.1 Tubular tower
+
+If telecom cables are placed inside a tubular tower, the total lightning current flows through the tower and no current flows through the cable, so that  $\alpha_T = 0$ . Of course, this is an approximation that neglects the tower resistance. Otherwise, a more detailed calculation is needed, which takes into account the tower resistance. In this case, the cables are affected by the electric field developed along the internal surface of the tower. This electric field is given by the product of the internal surface impedance of the tower and the current in the tower.
+
+If telecom cables are placed outside the tower, the distribution of current is determined by equations (7) or (8), which are rewritten here as equations (10) and (11), with the tower radius as  $r_t$ , the conductor radius as  $r_c$ , and the distance between the two axes as  $d$ .
+
+$$\alpha_T = \ln\left(\frac{d-r_c}{r_t}\right) / \ln\left[\frac{(d-r_c)(b-r_t)}{r_c r_t}\right] \quad (10)$$
+
+$$\alpha_T = \ln\left(\frac{d}{r_t}\right) / \ln\left(\frac{d^2}{r_t r_c}\right) \quad (11)$$
+
+Usually, there are several conductors in parallel, such as coaxial feeders and power cables. In this case,  $r_c$  is the geometric mean radius (GMR) of a bundle of conductors. Annex A describes the calculation of the GMR. Figure 3 shows a cross-sectional view of the situation considered for a tubular tower.
+
+It is important to highlight that, when the distance  $d$  between the two axes is not much larger than the tower radius  $r_t$ , some proximity effects arise. The result is that the current in the tower is no longer radially uniform, with the tower side opposite to the conductors carrying a higher current density and more current in the tower is required to fulfill the boundary condition described by equation (1). Therefore, neglecting the proximity effects in this calculation is a safe-side approach, as it leads to a shielding factor somewhat higher than the one obtained when the proximity effects are considered.
+
+As an example of calculation, consider a tower radius  $r_t = 150$  mm, a bundle of conductors with GMR  $r_c = 50$  mm, and a distance between the two axes  $d = 260$  mm. As in this case  $d$  is not much greater than  $r_t$ , equation (10) should be used, which provides  $\alpha_T = 0.30$ .
+
+![Diagram of a tubular tower and a bundle of conductors.](c78c2eefd86269d1740ab85a916f24f2_img.jpg)
+
+A cross-sectional diagram showing a large circle on the left labeled "Tower" with radius
+
+ $r_t$ 
+
+. To its right is a smaller circle labeled "Bundle of conductors" with radius
+
+ $r_c$ 
+
+. A horizontal line segment labeled
+
+ $d$ 
+
+connects the center of the tower circle to the center of the bundle circle. A vertical line segment extends from the center of the tower circle down to its circumference, representing the radius
+
+ $r_t$ 
+
+.
+
+Diagram of a tubular tower and a bundle of conductors.
+
+Figure 3 – Distances for tubular tower
+
+#### 6.3.2 Three-legged tower
+
+Applying the same rationale to a three-legged tower, the following typical situations can be found, where the distance  $d$  is the distance from a leg to the axis of the tower. For towers in a pyramidal configuration,  $d$  shall be averaged along the tower.
+
+- Bundle of cables at an arbitrary distance  $s$  from one leg. See Figure 4 (a).
+
+$$\alpha_T = \left\{ 1 + \frac{3 \ln(s/r_c)}{\ln[s(3d^2 + s^2 - 3ds)/3r_t d^2]} \right\}^{-1} \quad (12)$$
+
+- Bundle of cables in the centre of the tower ( $s = d$ ). See Figure 4 (b).
+
+$$\alpha_T = \left[ 1 + \frac{3 \ln(d/r_c)}{\ln(d/3r_t)} \right]^{-1} \quad (13)$$
+
+- Cable in one side of the tower ( $s = 3d/2$ ). See Figure 4 (c).
+
+$$\alpha_T = \left[ 1 + \frac{3 \ln(3d/2r_c)}{\ln(3d/8r_t)} \right]^{-1} \quad (14)$$
+
+- Cable near one leg ( $s \ll d$ ). See Figure 4 (d).
+
+$$\alpha_T = \left[ 1 + \frac{3 \ln(s/r_c)}{\ln(s/r_t)} \right]^{-1} \quad (15)$$
+
+![Figure 4: Distances for three-legged tower. The figure consists of four sub-diagrams (a, b, c, d) arranged in a 2x2 grid. Each diagram shows a three-legged tower with legs at the vertices of an equilateral triangle. The distance from the center (Tower axis) to each leg is labeled 'd'. A bundle of conductors is shown in different positions: (a) at an arbitrary distance 's' from one leg; (b) at the center of the tower (s = d); (c) on one side of the tower (s = 3d/2); and (d) very close to one leg (s << d).](78ffccd66df9bafd96e3e081110d09dd_img.jpg)
+
+Figure 4: Distances for three-legged tower. The figure consists of four sub-diagrams (a, b, c, d) arranged in a 2x2 grid. Each diagram shows a three-legged tower with legs at the vertices of an equilateral triangle. The distance from the center (Tower axis) to each leg is labeled 'd'. A bundle of conductors is shown in different positions: (a) at an arbitrary distance 's' from one leg; (b) at the center of the tower (s = d); (c) on one side of the tower (s = 3d/2); and (d) very close to one leg (s << d).
+
+**Figure 4 – Distances for three-legged tower**
+
+#### 6.3.3 Four-legged tower
+
+For a four-legged tower, the following typical situations can be found:
+
+- Cable at an arbitrary distance  $s$  from one leg. See Figure 5 (a).
+
+$$\alpha_T = \left\{ 1 + \frac{4 \ln(s/r_c)}{\ln[s(2d - s)/2r_t d]} \right\}^{-1} \quad (16)$$
+
+- Cable in the centre of the tower ( $s = d$ ). See Figure 5 (b).
+
+$$\alpha_T = \left[ 1 + \frac{4 \ln(d/r_c)}{\ln(d/2r_t)} \right]^{-1} \quad (17)$$
+
+- Cable near one leg ( $s \ll d$ ). See Figure 5 (c).
+
+$$\alpha_T = \left[ 1 + \frac{4 \ln(s/r_c)}{\ln(s/2r_t)} \right]^{-1} \quad (18)$$
+
+![Figure 5: Distances for four-legged tower. The figure consists of three sub-diagrams labeled (a), (b), and (c). Each diagram shows a cross-section of a four-legged tower with legs at the corners of a square. A dashed line represents the tower axis. (a) shows a bundle of conductors located at a distance 's' from one of the tower legs. (b) shows a bundle of conductors located at the center of the tower, on the tower axis. (c) shows a bundle of conductors located at a distance 's' from one of the tower legs, similar to (a) but with a different orientation. The distance 'd' is indicated as the distance from a tower leg to the tower axis.](cab0834804fb031b43865554cc8d06ab_img.jpg)
+
+Figure 5: Distances for four-legged tower. The figure consists of three sub-diagrams labeled (a), (b), and (c). Each diagram shows a cross-section of a four-legged tower with legs at the corners of a square. A dashed line represents the tower axis. (a) shows a bundle of conductors located at a distance 's' from one of the tower legs. (b) shows a bundle of conductors located at the center of the tower, on the tower axis. (c) shows a bundle of conductors located at a distance 's' from one of the tower legs, similar to (a) but with a different orientation. The distance 'd' is indicated as the distance from a tower leg to the tower axis.
+
+Figure 5 – Distances for four-legged tower
+
+## 6.4 Cable trays and bundle of cables
+
+Although the same rationale described in clause 6.1 applies to the case of having several cables in parallel, as in the bundle of cables and cables placed in a metallic tray, the lack of symmetry in the cable distribution prevents the development of generic formulas. Indeed, the shielding factor calculation for these complex cases often requires a dedicated numeric routine. In these routines, conductors of arbitrary cross-sectional profile may be represented by a number of cylindrical conductors disposed in the way as to form the desired profile.
+
+For specific cases and using some approximations, it is possible to derive analytical expressions for the shielding factors. An example is shown in Figure 6 (a), where a feeder cable is placed in the middle of a ladder cable tray that runs along the tower. This situation is shown in Figure 6 (b), where the two lateral bars of the cable tray are replaced by equivalent cylindrical conductors. The radius of the equivalent conductor ( $r_b$ ) is calculated with the procedure described in Annex A.
+
+For the situation shown in Figure 6 (b), and considering that the cable is placed in the middle of the tray ( $s = a/2$ ), the shielding factor can be easily calculated as:
+
+$$\alpha_F = \frac{\ln(s/2r_b)}{\ln(s^3/2r_c^2 r_b)} \quad (19)$$
+
+For instance, considering that the lateral bars in Figure 6 have a height  $b = 50$  mm and a width that is negligible, Annex A gives  $r_b = 16$  mm. For  $r_c = 4$  mm and  $s = 100$  mm, equation (19) gives  $\alpha_F = 0.15$ . If the cable tray is smaller ( $s = 50$  mm), its shielding factor drops to  $\alpha_F = 0.08$ .
+
+![Figure 6: Representation of a ladder tray by cylindrical conductors. (a) shows a cross-section of a ladder tray with two vertical rails of height h and thickness e, connected by a horizontal rung. A cable of radius rc is positioned on the rung at a distance S from the right rail. The distance between the centers of the rails is d. (b) shows the equivalent model using three cylindrical conductors. The two outer conductors represent the rails, with a radius rb = 0.318(h + e). The central conductor represents the cable with radius rc. The distance between the centers of the outer conductors is d, and the distance from the center of the central conductor to the right outer conductor is S.](0dd5ee731e9d7e34e498b5c926110773_img.jpg)
+
+Figure 6: Representation of a ladder tray by cylindrical conductors. (a) shows a cross-section of a ladder tray with two vertical rails of height h and thickness e, connected by a horizontal rung. A cable of radius rc is positioned on the rung at a distance S from the right rail. The distance between the centers of the rails is d. (b) shows the equivalent model using three cylindrical conductors. The two outer conductors represent the rails, with a radius rb = 0.318(h + e). The central conductor represents the cable with radius rc. The distance between the centers of the outer conductors is d, and the distance from the center of the central conductor to the right outer conductor is S.
+
+**Figure 6 – Representation of a ladder tray by cylindrical conductors**
+
+## 7 Earthing connection of cables
+
+This clause presents the rationale for the refraction factor  $\delta$  considered in [ITU-T K.46].
+
+Lightning flashes produce electromagnetic fields that induce impulsive voltages on aerial and buried telecommunication lines. These voltages are primarily induced in common-mode, i.e., the voltage is developed between the cable conductors and earth. The connection of the cable to earth reduces significantly the voltage (and current) that propagates along the line. This earthing connection may be done in two ways, depending on the type of cable:
+
+- 1) Unshielded cables: the connection of the telecommunication conductors to earth is carried out by using surge protective components (SPCs), e.g., a gas discharge tube (GDT).
+- 2) Shielded cables: the shield is usually connected direct to the earthing electrode.
+
+This clause presents the rationale for the evaluation of the shielding effect provided by this earthing connection. For unshielded cables, the voltage developed across the SPC (e.g., arc voltage of a GDT) is neglected, so that the same model applies to shielded and unshielded cables.
+
+This shielding effect is referred to here as the refraction factor ( $\delta$ ), in order to be in line with [ITU-T K.46]. The refraction factor ( $\delta$ ) is defined as the ratio of the surge voltage travelling in the line after passing through a discontinuity in its surge impedance and the surge that would travel in the line if there was no discontinuity in its surge impedance. The earthing connections of the line and the transition from buried to aerial installation (and vice versa) are examples of discontinuity in the line surge impedance.
+
+Figure 7 (a) represents the refraction factor calculation, where the incident voltage wave  $V_1(t)$  that propagates along a line with surge impedance  $Z_1$  towards a discontinuity represented by an earthing connection and a change in the line surge impedance. As the incident wave reaches the discontinuity, it produces the refracted voltage  $V_2(t)$  that is developed across the earthing connection  $R_g$  and propagates downline with surge impedance  $Z_2$ , as shown in Figure 7 (b). A reflected voltage  $V_R(t)$  is also produced at the discontinuity, which travels back upline.
+
+![Figure 7: Incident voltage V1(t) arriving at a line discontinuity (a) and the resulting reflected VR(t) and refracted V2(t) voltages (b).](33ed1f9b27c7c21c797aa928b0f06851_img.jpg)
+
+The diagram consists of two parts, (a) and (b), illustrating voltage wave propagation on a transmission line with a discontinuity and an earthing connection.
+
+Part (a) shows an incident voltage wave  $V_1(t)$  traveling from left to right on a line with characteristic impedance  $Z_1$ . At a certain point, the line impedance changes to  $Z_2$ . At this discontinuity, there is an earthing connection through a resistor  $R_g$  to ground.
+
+Part (b) shows the result after the incident wave has reached the discontinuity. A reflected voltage wave  $V_R(t)$  is shown traveling back to the left on the  $Z_1$  line. A refracted voltage wave  $V_2(t)$  is shown traveling to the right on the  $Z_2$  line. The earthing connection  $R_g$  remains at the discontinuity point.
+
+Figure 7: Incident voltage V1(t) arriving at a line discontinuity (a) and the resulting reflected VR(t) and refracted V2(t) voltages (b).
+
+**Figure 7 – Incident voltage  $V_1(t)$  arriving at a line discontinuity (a) and the resulting reflected  $V_R(t)$  and refracted  $V_2(t)$  voltages (b)**
+
+It is clear that the voltage at the discontinuity is given by:
+
+$$V_2(t) = V_1(t) + V_R(t) \quad (20)$$
+
+Due to the energy conservation, the instantaneous power delivered by the incident voltage  $V_1(t)$  must be equal to the power carried by the refracted voltage  $V_2(t)$ , carried by the reflected voltage  $V_R(t)$ , and dissipated in the earthing resistance  $R_g$ , which gives:
+
+$$\frac{V_1^2(t)}{Z_1} = \frac{V_2^2(t)}{Z_2} + \frac{V_R^2(t)}{Z_1} + \frac{V_2^2(t)}{R_g} \quad (21)$$
+
+Inserting  $V_R(t)$  from equation (20) into equation (21) and rearranging yields the refraction factor:
+
+$$\delta = \frac{V_2(t)}{V_1(t)} = \frac{2 Z_2 R_g}{Z_1 R_g + Z_2 R_g + Z_1 Z_2} \quad (22)$$
+
+An example of the application of equation (22) is a lightning surge induced in an aerial line ( $Z_1 = 400 \Omega$ ) being propagated towards a buried line ( $Z_2 = 100 \Omega$ ). At the transition between the aerial and buried cables, there is an earthing connection with  $30 \Omega$  resistance. Inserting these values into equation (22) gives the refraction factor  $\delta = 0.11$ . Considering that the incident common mode surge has a  $40 \text{ kV}$  peak value, the common mode voltage in the buried cable is  $40 \times 0.11 = 4.4 \text{ kV}$ .
+
+Some specific situations may be derived from equation (22). For instance, if the line stops at the earthing connection, then  $Z_2 = \infty$ . This condition gives:
+
+$$\delta = \frac{2 R_g}{R_g + Z_1} \quad (23)$$
+
+Similarly, if there is no earthing connection, but just a transition in the line surge impedance (e.g., from aerial to underground), then  $R_g = \infty$  and the refraction factor becomes:
+
+$$\delta = \frac{2 Z_2}{Z_2 + Z_1} \quad (24)$$
+
+If there is no earthing connection and the line stops at that point, then  $Z_2 = \infty$  and  $R_g = \infty$ , which leads to  $\delta = 2$ , i.e., the incoming voltage doubles at the open line end. On the other hand, if there is an
+
+earthing connection at the end of the line ( $Z_2 = \infty$ ) and its value is equal to the incoming line impedance ( $R_g = Z_1$ ), then  $\delta = 1$  and the line is said to be matched to earth at this point.
+
+## 8 Shielding factor of telecommunication cables
+
+This clause presents the rationale for the shielding factor  $\eta$  of cables considered in [ITU-T K.46].
+
+Figure 8 shows a tubular shielded telecommunication cable with its shield connected to earth at both ends through earthing resistances ( $R_g$ ) equal to the cable surge impedance ( $Z$ ), so that there is no reflection of the common mode voltages. A more general case with reflections from the cable ends can be derived from the model shown in Figure 8 by applying the superposition theorem on the voltages generated by each reflection.
+
+![Figure 8: Equivalent circuit for shielded telecommunication cable. The diagram shows a horizontal line representing the cable. At the left end, a vertical resistor labeled R_g = Z connects the line to ground. At the right end, another vertical resistor labeled R_g = Z connects the line to ground. A voltage U(t) is indicated by a vertical arrow pointing upwards from the ground at the left end. A voltage V(t) is indicated by a vertical arrow pointing upwards from the ground at the center of the line.](16152cf1d84aea10848758f51a91ff6a_img.jpg)
+
+Figure 8: Equivalent circuit for shielded telecommunication cable. The diagram shows a horizontal line representing the cable. At the left end, a vertical resistor labeled R\_g = Z connects the line to ground. At the right end, another vertical resistor labeled R\_g = Z connects the line to ground. A voltage U(t) is indicated by a vertical arrow pointing upwards from the ground at the left end. A voltage V(t) is indicated by a vertical arrow pointing upwards from the ground at the center of the line.
+
+**Figure 8 – Equivalent circuit for shielded telecommunication cable**
+
+Consider that the common mode voltage  $V(t)$  is propagating in the line. The current associated with this voltage is:
+
+$$I(t) = \frac{V(t)}{Z} \quad (25)$$
+
+where  $Z$  is the common mode surge impedance of the line. Equation (25) assumes that the shield resistance  $R_s$  is much smaller than the cable common mode surge impedance  $Z$ , which is a reasonable assumption for regular shielded telecommunication cables.
+
+The voltage  $U(t)$  developed between the pairs and the shield is given by the voltage drop in the cable shield:
+
+$$U(t) = I(t)R_s \quad (26)$$
+
+where  $R_s$  is the internal surface impedance with external current return. For the low frequency, the internal surface impedance can be approximated by the direct current (DC) resistance of the shield.
+
+Note that there are some conditions behind equation (25):
+
+- the shield is tubular, so that no magnetic field leaks to the interior of the shield;
+- for frequency bandwidth considered, the skin depth is significantly larger than the shield thickness, which is reasonable for lightning surges and shielded telecommunication cables;
+- the pairs are terminated to the shield at one cable end and they are open at the other end (see Figure 8), which is a conservative approximation for telecommunication lines.
+
+Substituting  $I(t)$  from equation (24) into equation (25) yields:
+
+$$\eta = \frac{U(t)}{V(t)} = \frac{R_s}{Z} \quad (27)$$
+
+The shielding factor as per equation (27) shall be used only when the simplifying conditions considered in its development apply.
+
+## Annex A
+
+### Geometric mean radius of conductors
+
+(This annex forms an integral part of this Recommendation.)
+
+Table A.1 gives the GMR for typical conductor arrangements.
+
+**Table A.1 – Geometric mean radius of conductors**
+
+| Conductor(s)                | Illustration   | Geometric mean radius                                                                          |
+|-----------------------------|----------------|------------------------------------------------------------------------------------------------|
+| Solid circular conductor    | Figure A.1 (a) | $r$                                                                                            |
+| Solid rectangular conductor | Figure A.1 (b) | $0.318 (a + b)$                                                                                |
+| Seven strand conductor      | Figure A.1 (c) | $r$                                                                                            |
+| Two parallel conductors     | Figure A.1 (d) | $(d^2 r_1 r_2)^{1/4}$                                                                          |
+| Three parallel conductors   | Figure A.1 (e) | $(d_{12}^2 d_{13}^2 d_{23}^2 r_1 r_2 r_3)^{1/9}$                                               |
+| $n$ Parallel conductors     | –              | $(d_{12}^2 d_{13}^2 \dots d_{1n}^2 d_{23}^2 \dots d_{(n-1)n}^2 r_1 r_2 r_3 \dots r_n)^{1/n^2}$ |
+
+NOTE – Considering the inductive effects of lightning currents (high  $di/dt$ ), the conductor internal magnetic flux has been neglected (perfect skin effect). For groups of conductors, symmetric current density at each conductor's periphery has been taken into account (the proximity effect has been neglected).
+
+![Figure A.1 shows five diagrams illustrating typical conductor arrangements: (a) a solid circular conductor with radius r; (b) a solid rectangular conductor with width a and height b; (c) a seven-strand conductor with radius r; (d) two parallel conductors with radii r1 and r2 separated by distance d; (e) three parallel conductors with radii r1, r2, and r3, with distances d12, d13, and d23 between them.](f7bc9b0327ed4589a3faf9a7b3c92712_img.jpg)
+
+Figure A.1 shows five diagrams illustrating typical conductor arrangements: (a) a solid circular conductor with radius r; (b) a solid rectangular conductor with width a and height b; (c) a seven-strand conductor with radius r; (d) two parallel conductors with radii r1 and r2 separated by distance d; (e) three parallel conductors with radii r1, r2, and r3, with distances d12, d13, and d23 between them.
+
+**Figure A.1 – Geometric mean radius of typical conductors**
+
+
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                             |
+|-----------------|---------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                           |
+| Series D        | General tariff principles                                                                   |
+| Series E        | Overall network operation, telephone service, service operation and human factors           |
+| Series F        | Non-telephone telecommunication services                                                    |
+| Series G        | Transmission systems and media, digital systems and networks                                |
+| Series H        | Audiovisual and multimedia systems                                                          |
+| Series I        | Integrated services digital network                                                         |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals |
+| <b>Series K</b> | <b>Protection against interference</b>                                                      |
+| Series L        | Construction, installation and protection of cables and other elements of outside plant     |
+| Series M        | Telecommunication management, including TMN and network maintenance                         |
+| Series N        | Maintenance: international sound programme and television transmission circuits             |
+| Series O        | Specifications of measuring equipment                                                       |
+| Series P        | Terminals and subjective and objective assessment methods                                   |
+| Series Q        | Switching and signalling                                                                    |
+| Series R        | Telegraph transmission                                                                      |
+| Series S        | Telegraph services terminal equipment                                                       |
+| Series T        | Terminals for telematic services                                                            |
+| Series U        | Telegraph switching                                                                         |
+| Series V        | Data communication over the telephone network                                               |
+| Series X        | Data networks, open system communications and security                                      |
+| Series Y        | Global information infrastructure, Internet protocol aspects and next-generation networks   |
+| Series Z        | Languages and general software aspects for telecommunication systems                        |

marked/K/T-REC-K.103-201503-I_PDF-E/raw.md

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+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**K.103**
+
+(03/2015)
+
+SERIES K: PROTECTION AGAINST INTERFERENCE
+
+---
+
+**Surge protective component application guide –  
+Silicon PN junction components**
+
+Recommendation ITU-T K.103
+
+ITU-T
+
+![ITU logo: A globe with a red lightning bolt striking it, with the text 'ITU International Telecommunication Union' to the right.](84a1d09fb489061482111515543b60dc_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with a red lightning bolt striking it from the top right. To the right of the globe, the text "ITU" is written in a bold, blue, sans-serif font, and below it, "International Telecommunication Union" is written in a smaller, blue, sans-serif font.
+
+ITU logo: A globe with a red lightning bolt striking it, with the text 'ITU International Telecommunication Union' to the right.
+
+
+
+# Recommendation ITU-T K.103
+
+# Surge protective component application guide – Silicon PN junction components
+
+## Summary
+
+Recommendation ITU-T K.103 describes the construction, characteristics, ratings and application examples of surge protective components (SPCs), having one or two silicon PN junctions, intended for the protection of exchange and outdoor equipment, subscriber or customer equipment and telecommunication lines from surges. The PN junction technologies covered are: Zener breakdown, avalanche breakdown, fold-back, punch-through and rectification.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T K.103    | 2015-03-01 | 5           | <a href="http://handle.itu.int/11.1002/1000/12423">11.1002/1000/12423</a> |
+
+## Keywords
+
+Application circuits, array, avalanche, electrical characteristics, electrical ratings, fold-back, punch-through, rectification, Zener.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2015
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+###### Page
+
+|     |                                                                  |    |
+|-----|------------------------------------------------------------------|----|
+| 1   | Scope.....                                                       | 1  |
+| 2   | References.....                                                  | 1  |
+| 3   | Definitions .....                                                | 1  |
+| 3.1 | Terms defined elsewhere .....                                    | 1  |
+| 3.2 | Terms defined in this Recommendation.....                        | 2  |
+| 4   | Abbreviations and acronyms .....                                 | 2  |
+| 5   | Conventions .....                                                | 3  |
+| 6   | Construction.....                                                | 3  |
+| 6.1 | Packaging .....                                                  | 3  |
+| 6.2 | Semiconductor junction structure and electrical properties ..... | 4  |
+| 7   | Characteristics.....                                             | 10 |
+| 7.1 | Stand-off or maximum reverse working voltage, VRWM.....          | 11 |
+| 7.2 | Breakdown voltage, $V_{(BR)}$ .....                              | 11 |
+| 7.3 | Clamping voltage, VC .....                                       | 12 |
+| 7.4 | Punch-through voltage $V_{(PT)}$ .....                           | 13 |
+| 7.5 | Snap back voltage $V_{(SB)}$ .....                               | 13 |
+| 7.6 | Forward biased PN junction voltage, VF .....                     | 13 |
+| 7.7 | Junction capacitance, CJ.....                                    | 15 |
+| 7.8 | Package inductance .....                                         | 17 |
+| 8   | Ratings .....                                                    | 17 |
+| 8.1 | Peak pulse current, IPP .....                                    | 17 |
+| 8.2 | Maximum peak pulse power, PPPM .....                             | 19 |
+| 8.3 | Power dissipation, PD .....                                      | 19 |
+| 9   | Application examples .....                                       | 20 |
+| 9.1 | Series connection.....                                           | 20 |
+| 9.2 | Parallel connection .....                                        | 21 |
+| 9.3 | DC supply protection.....                                        | 21 |
+| 9.4 | Power frequency protection.....                                  | 23 |
+| 9.5 | Signal protection.....                                           | 24 |
+|     | Bibliography.....                                                | 29 |
+
+
+
+# Recommendation ITU-T K.103
+
+## Surge protective component application guide – Silicon PN junction components
+
+# 1 Scope
+
+This Recommendation in the surge protective component application guide series covers voltage limiting components, having one or two silicon PN junctions. These surge protective components (SPCs) are clamping type overvoltage protectors [b-ITU-T K.96]. Components covered in this Recommendation use the following PN junction technologies: Zener breakdown, avalanche breakdown, fold-back, punch-through and rectification. Guidance is given on construction, characteristics, ratings and application examples.
+
+# 2 References
+
+This Recommendation does not contain any normative references.
+
+# 3 Definitions
+
+## 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 avalanche breakdown (of a PN junction)** [b-IEC 60050-521]: Breakdown that is caused by the cumulative multiplication of charge carriers in a semiconductor under the action of a strong electric field, which causes some carriers to gain enough energy to liberate new hole-electron pairs by ionization.
+
+**3.1.2 bidirectional transistor** [b-IEC 60050-521]: Transistor, which has substantially the same electrical characteristics when the terminals normally designated as emitter and collector are interchanged.
+
+**3.1.3 bipolar junction transistor** [b-IEC 60050-521]: Transistor having at least two junctions and whose functioning depends on both majority carriers and minority carriers.
+
+**3.1.4 breakdown (of a reverse-biased PN junction)** [b-IEC 60050-521]: Phenomenon, the initiation of which is observed as a transition from a state of high dynamic resistance to a state of substantially lower dynamic resistance for increasing magnitude of reverse current.
+
+**3.1.5 common mode conversion** [b-ITU-T K.96]: Process by which a differential mode electrical signal is produced in response to a common mode electrical signal.
+
+**3.1.6 common mode surge** [b-ITU-T K.96]: Surge appearing equally on all conductors of a group at a given location.
+
+NOTE 1 – The reference point for common mode surge voltage measurement can be a chassis terminal, or a local earth/ground point.
+
+NOTE 2 – Common mode surge is also known as longitudinal surge or asymmetrical surge.
+
+**3.1.7 differential mode surge** [b-ITU-T K.96]: Surge occurring between any two conductors or two groups of conductors at a given location.
+
+NOTE 1 – The surge source maybe be floating, without a reference point or connected to reference point, such as a chassis terminal, or a local earth/ground point.
+
+NOTE 2 – Differential mode surge is also known as metallic surge or transverse surge or symmetrical surge or normal surge.
+
+**3.1.8 diode (semiconductor)** [b-IEC 60050-521]: Two-terminal semiconductor device having an asymmetrical voltage-current characteristic.
+
+NOTE – Unless otherwise qualified, this term usually means a device with the voltage-current characteristic typical of a single PN junction.
+
+**3.1.9 fold-back breakdown (of a bidirectional transistor)** [b-ITU-T K.96]: Re-entrant breakdown characteristic caused by transistor action producing a region of negative dynamic resistance before reverting back to a low positive dynamic resistance condition.
+
+NOTE – In transistor terms, the initial breakdown is in the  $BV_{CBO}$  mode, which changes to the lower voltage  $BV_{CEO}$  mode as the breakdown current increases.
+
+**3.1.10 overcurrent** [b-ITU-T K.96]: Any current having a peak value exceeding the corresponding peak value of maximum steady-state current at normal operating conditions.
+
+**3.1.11 overvoltage** [b-IEC 60664-2-1]: Any voltage having a peak value exceeding the corresponding peak value of maximum steady-state voltage at normal operating conditions.
+
+**3.1.12 power fault** [b-ITU-T K.96]: Abnormal fault condition, when the local AC power service is in electrical contact (power contact) or is magnetically coupled (power induction) to another service.
+
+**3.1.13 PN junction** [b-IEC 61836]: Junction between a P-type semiconductor and an N-type semiconductor.
+
+**3.1.14 punch-through (between two PN junctions)** [b-IEC 60050-521]: Contact between the space charge regions of two PN junctions as a result of widening of one or both of them.
+
+**3.1.15 surge** [b-ITU-T K.96]: Temporary disturbance on the conductors of an electrical service caused by an electrical event not related to the service.
+
+NOTE – For non-linear SPCs a surge event is defined as an overvoltage or overcurrent or both.
+
+**3.1.16 surge protective component (SPC)** [b-ITU-T K.96]: Component specifically included in a device or equipment for the mitigation of the onward propagation of overvoltages or overcurrents or both.
+
+**3.1.17 surge protective device (SPD)** [b-ITU-T K.96]: Device that mitigates the onward propagation of overvoltages or overcurrents or both.
+
+**3.1.18 Zener breakdown (of a PN junction)** [b-IEC 60050-521]: Breakdown caused by the transition of electrons from the valence band to the conduction band due to tunnel action under the influence of a strong electric field in a PN junction.
+
+## 3.2 Terms defined in this Recommendation
+
+None.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|           |                                                     |
+|-----------|-----------------------------------------------------|
+| AC        | Alternating Current                                 |
+| DC        | Direct Current                                      |
+| HDSL      | High-bit-rate Digital Subscriber Line               |
+| HFE       | Hybrid model Forward current gain in common Emitter |
+| IC        | Integrated Circuit                                  |
+| ICT       | Information and Communications Technology           |
+| $I_{PP}$  | Peak Pulse current                                  |
+| $I_{PPM}$ | Maximum Peak Pulse current                          |
+| $I_R$     | Reverse current                                     |
+
+|                   |                                               |
+|-------------------|-----------------------------------------------|
+| MOV               | Metal-Oxide Varistor                          |
+| NASA              | National Aeronautics and Space Administration |
+| PD                | Powered Device                                |
+| PHY               | Physical Layer (usually Ethernet transceiver) |
+| PLC               | Power Line Communication                      |
+| $P_{\text{PPM}}$  | Maximum Peak Pulse Power                      |
+| PSE               | Power Sourcing Equipment                      |
+| SDSL              | Symmetrical Digital Subscriber Line           |
+| SELV              | Safety Extra Low Voltage                      |
+| SPC               | Surge Protective Component                    |
+| SPD               | Surge Protective Device                       |
+| USB               | Universal Serial Bus                          |
+| $V_{(\text{BR})}$ | Breakdown Voltage                             |
+| $V_{\text{C}}$    | Clamping Voltage                              |
+| $V_{\text{CM}}$   | Maximum Clamping Voltage                      |
+| $V_{\text{F}}$    | Forward Voltage                               |
+| $V_{(\text{PT})}$ | Punch-Through Voltage                         |
+| $V_{\text{R}}$    | Reverse Voltage                               |
+| $V_{\text{RWM}}$  | Maximum Reverse Working Voltage               |
+| $V_{(\text{SB})}$ | Snapback Voltage                              |
+
+# 5 Conventions
+
+None.
+
+# 6 Construction
+
+## 6.1 Packaging
+
+There are two types of component packaging used with printed circuit boards: through-hole or surface-mount. Through-hole packaging is typically axial lead or side leaded. Surface-mount packaging may be leaded or with solderable pads. Figure 1 shows examples of these four package types.
+
+![Figure 1 shows four example component packages (left to right): a through-hole axial leaded diode, a TO-220 style through-hole package with three leads, a surface-mount (SMD) diode package, and a multi-pad surface-mount package.](e7cb11f042fc58088dff4b6d9306845e_img.jpg)
+
+Figure 1 shows four example component packages (left to right): a through-hole axial leaded diode, a TO-220 style through-hole package with three leads, a surface-mount (SMD) diode package, and a multi-pad surface-mount package.
+
+**Figure 1 – Example component packages (left to right): through-hole, axial and side leaded, surface-mount, leaded and pad**
+
+## **6.2 Semiconductor junction structure and electrical properties**
+
+This clause describes in simple terms the semiconductor chip structure, operation, circuit symbol and basic characteristics. For in depth information on these topics, text books on this subject, such as [b-Lindmayer] or [b-Baliga], should be referenced.
+
+### **6.2.1 Single PN junction structure and electrical characteristic**
+
+Figure 2 shows a diagram of a simple PN junction structure. Metallization is applied to the top and bottom of the structure for electrical contact. The N-type silicon region has negative carriers (electrons) and the P-type silicon region effectively has positive carriers (holes). The junction is formed where the material changes from N-type to P-type. A depletion layer is formed at the junction. The depletion region presents a threshold voltage that must be overcome before current can flow. If a voltage is applied with a positive polarity to the P region and negative polarity to the N region, for voltages above about 0.3 V, current will start to flow. Under these bias conditions the PN junction is termed as being forward biased. Voltages that exceed the threshold voltage will be limited to the forward voltage ( $V_F$ ) characteristic value for the level of available current from the source of the voltage.
+
+The Figure 2 graph shows an example of a PN junction forward biased characteristic plotted as forward current,  $I_F$ , against forward voltage,  $V_F$  over six decades of current. Above 1 A the voltage starts to increase rapidly as the material starts to run out of inherent current carriers.
+
+The symbol shown next to the structure is for a general purpose rectifier diode.
+
+![Figure 2: Forward biased PN junction structure, rectifier diode circuit symbol and electrical forward characteristic. The top part shows a cross-section of a PN junction with P and N regions, metal contacts, and a depletion layer, connected to a forward bias circuit. The middle part shows the standard diode circuit symbol. The bottom part is a log-linear graph of forward current (I_F) versus forward voltage (V_F).](d48475a25698b1c0592e4cfe07138f2a_img.jpg)
+
+The figure illustrates the structure and characteristics of a forward-biased PN junction. The top section shows a cross-section of the junction with P-type and N-type semiconductor regions, metal contacts, and a depletion layer, connected to a forward bias circuit. The middle section shows the standard rectifier diode circuit symbol. The bottom section is a graph of the electrical forward characteristic, plotting forward current ( $I_F$ ) in Amperes (A) on a logarithmic scale against forward voltage ( $V_F$ ) in Volts (V) on a linear scale.
+
+| Forward voltage, $V_F$ (V) | Forward current, $I_F$ (A) |
+|----------------------------|----------------------------|
+| 0.3                        | $10^{-5}$                  |
+| 0.6                        | $10^{-2}$                  |
+| 0.9                        | $10^{-1}$                  |
+| 1.2                        | $10^0$                     |
+
+Figure 2: Forward biased PN junction structure, rectifier diode circuit symbol and electrical forward characteristic. The top part shows a cross-section of a PN junction with P and N regions, metal contacts, and a depletion layer, connected to a forward bias circuit. The middle part shows the standard diode circuit symbol. The bottom part is a log-linear graph of forward current (I\_F) versus forward voltage (V\_F).
+
+**Figure 2 – Forward biased PN junction structure, rectifier diode circuit symbol and electrical forward characteristic**
+
+Single PN junction voltage limiting can only be used where either the signal is a few hundred millivolts or the signal or direct current (DC) supply is in the opposite polarity. The range of applications can be extended by using multiple diodes, either connecting the diodes in series or placing other diodes in the opposite polarity in parallel or both; see Figure 3. Four diodes can be used to create a bridge rectifier, useful to make unidirectional breakdown voltage ( $V_{(BR)}$ ) limiters into bidirectional voltage limiters.
+
+A commercial example of the eight diode array has a total forward voltage of 2.4 V at 1 mA and 3.9 V at 1 A. Connecting four diodes in series reduces the array capacitance to 13 pF. The array has a 30 A 10/1000 rating.
+
+![Figure 3 shows three different rectifier diode array configurations. The first (left) consists of two diodes connected in anti-parallel between two terminals. The second (middle) is a bridge-like configuration with four diodes. The third (right) is a vertical stack of four anti-parallel diode pairs connected in series. A label 'K.103(15)_F03' is located below the third array.](d4af765160d04ecef538e5066006dc77_img.jpg)
+
+Figure 3 shows three different rectifier diode array configurations. The first (left) consists of two diodes connected in anti-parallel between two terminals. The second (middle) is a bridge-like configuration with four diodes. The third (right) is a vertical stack of four anti-parallel diode pairs connected in series. A label 'K.103(15)\_F03' is located below the third array.
+
+**Figure 3 – Rectifier diode arrays**
+
+In Figure 4 the battery voltage is reversed compared with Figure 2. A negative polarity voltage is applied to the P region and a positive polarity voltage to the N region. The battery voltage adds to the natural depletion layer voltage and the depletion layer width expands to support the applied reverse voltage ( $V_R$ ). Under these bias conditions, the PN junction is termed as being reverse biased.
+
+The Figure 4 graph shows an example of a PN junction reverse biased characteristic plotted as reverse current ( $I_R$ ) against reverse voltage,  $V_R$ , over seven decades of current. The three characteristics shown are for breakdown diodes with nominal breakdown voltages of 3.6 V, 8.2 V and 15 V. The differences among these characteristics are discussed in clause 7. Voltages that exceed the characteristic voltage will be limited to the  $V_R$  characteristic value for the level of available current from the source of the voltage.
+
+The symbol shown next to the structure is for a PN junction component designed to be used in the reverse breakdown region. The small hook at the end of the diode symbol bar indicates a breakdown characteristic.
+
+![Figure 4: Reverse biased PN junction structure, breakdown diode circuit symbol and electrical reverse characteristics. The top part shows a cross-section of a PN junction with metalised contacts, a depletion layer, and a circuit symbol. The bottom part is a graph of reverse current (I_R) versus reverse voltage (V_R) for three breakdown voltages: 3.6 V, 8.2 V, and 15 V.](dd0f5301a5a6dd7c319701302110de88_img.jpg)
+
+The top part of Figure 4 shows a cross-section of a PN junction under reverse bias. It consists of a P-type semiconductor and an N-type semiconductor separated by a depletion layer, with metalised contacts at the ends. A circuit symbol for a breakdown diode is shown to the right. The bottom part is a graph of reverse current ( $I_{R}$ ) versus reverse voltage ( $V_{R}$ ). The x-axis ranges from -15 V to 0 V, and the y-axis is logarithmic, ranging from 10 mA to 1 nA. Three curves are shown: a dotted line for 3.6 V, a green dashed line for 8.2 V, and a solid red line for 15 V. The curves show that the reverse current increases sharply at the breakdown voltage.
+
+| Reverse Voltage $V_{R}$ (V) | 3.6 V Diode $I_{R}$ (A) | 8.2 V Diode $I_{R}$ (A) | 15 V Diode $I_{R}$ (A) |
+|-----------------------------|-------------------------|-------------------------|------------------------|
+| 0                           | < 1 n                   | < 1 n                   | < 1 n                  |
+| -2                          | ~10 n                   | < 1 n                   | < 1 n                  |
+| -3.6                        | ~10 m                   | < 1 n                   | < 1 n                  |
+| -6                          | -                       | ~10 n                   | < 1 n                  |
+| -8.2                        | -                       | ~10 m                   | < 1 n                  |
+| -12                         | -                       | -                       | ~10 n                  |
+| -15                         | -                       | -                       | ~10 m                  |
+
+Figure 4: Reverse biased PN junction structure, breakdown diode circuit symbol and electrical reverse characteristics. The top part shows a cross-section of a PN junction with metalised contacts, a depletion layer, and a circuit symbol. The bottom part is a graph of reverse current (I\_R) versus reverse voltage (V\_R) for three breakdown voltages: 3.6 V, 8.2 V, and 15 V.
+
+**Figure 4 – Reverse biased PN junction structure, breakdown diode circuit symbol and electrical reverse characteristics**
+
+This structure has a breakdown characteristic in one voltage polarity and forward diode characteristic in the opposite voltage polarity. These voltage-limiting unidirectional diodes are available with breakdown voltages in the range of 5 V to 500 V and peak power ratings of 400 W to 5 kW. In restricted voltage ranges, higher power components of 30 kW are available.
+
+Lower capacitance components can be produced by incorporating series and shunt rectifier diodes; see Figure 5. The unidirectional array is formed with series and shunt rectifiers. The bidirectional array uses two arms, each with a breakdown diode and rectifier. The bridged array uses four rectifier diodes in bridge connection and a breakdown diode. Further bridges can be added. For example four bridges can be used to protect eight digital integrated circuit (IC) signal connections. The bridged array has direct connections to the breakdown diode so that it can also protect a DC supply.
+
+![Figure 5: PN voltage limiter low capacitance arrays. The diagram shows five different circuit configurations: unidirectional, bidirectional, single bridged, and double bridged. Each configuration uses a combination of rectifier diodes and breakdown diodes to limit voltage.](cab0834804fb031b43865554cc8d06ab_img.jpg)
+
+The diagram shows five different circuit configurations for PN voltage limiter low capacitance arrays. From left to right: 1. A unidirectional array consisting of a breakdown diode in series with a rectifier diode. 2. A bidirectional array consisting of two unidirectional arrays connected in parallel with opposing polarities. 3. A single bridged array consisting of four rectifier diodes in a bridge configuration with a breakdown diode connected across the DC output of the bridge. 4. A double bridged array showing two input lines sharing a common bridge structure. 5. A multi-bridged array with four input lines connected to a central breakdown diode via rectifier bridges. The diagram is labeled K.103(15)\_F05.
+
+Figure 5: PN voltage limiter low capacitance arrays. The diagram shows five different circuit configurations: unidirectional, bidirectional, single bridged, and double bridged. Each configuration uses a combination of rectifier diodes and breakdown diodes to limit voltage.
+
+**Figure 5 – PN voltage limiter low capacitance arrays: unidirectional, bidirectional, single bridged and double bridged**
+
+### 6.2.2 NPN or PNP junction structures and electrical characteristics
+
+These three-layer voltage limiters are similar to NPN or PNP bipolar junction transistors without a base connection. A study of transistor characteristics is beneficial to understand how three-layer voltage limiters work.
+
+Figure 6 shows an NPN transistor structure and the two collector-voltage characteristics. The top N-type layer is designated as the collector, the middle P-type layer is the base and the bottom N-type layer is the emitter. Test voltages are applied with two connection configurations: collector-base and collector-emitter. The collector-base voltage,  $V_{CBO}$  characteristic, with the emitter unconnected, has the same characteristic as a breakdown diode shown in Figure 4. The collector-emitter voltage,  $V_{CEO}$  characteristic, with the base unconnected, is lower in voltage at higher currents than the  $V_{CBO}$  characteristic by a factor dependent on the current gain ( $H_{FE}$ ) (collector current/base current) of the transistor. The  $V_{CEO}$  characteristic depends on the collector-base leakage current. For low levels of leakage current, the characteristic initially follows the  $V_{CBO}$  characteristic until breakdown current starts to flow. The breakdown current is a base current, which will be amplified by the transistor current gain,  $H_{FE}$ . As a result the collector-emitter voltage reduces to a lower sustaining level. As the level of leakage current increases low-current "toe" in the  $V_{CEO}$  characteristic gradually reduces to nothing, see the three  $V_{CEO}$  characteristics in Figure 6.
+
+![Figure 6: NPN transistor structure, circuit symbol and electrical characteristics. The top part shows a cross-section of an NPN transistor with layers N (Collector), P (Base), and N (Emitter). It includes a circuit diagram with a battery for V_CBO and V_CEO, and a circuit symbol. The bottom part is a graph of Collector current vs. Collector voltage, showing V_CBO and V_CEO characteristics with high and low leakage curves.](0332672e127cd13bb6d2fc8d1e27bfa2_img.jpg)
+
+The figure illustrates the structure and characteristics of an NPN transistor. The top section shows a cross-section of the transistor with three layers: N (Collector), P (Base), and N (Emitter). A circuit diagram shows the base contact (B) connected to a battery for  $V_{CBO}$  and the emitter contact (E) connected to a battery for  $V_{CEO}$ . A circuit symbol for an NPN transistor is also shown. The bottom section is a graph of Collector current versus Collector voltage. It displays the  $V_{CBO}$  characteristic (Collector-base breakdown) and the  $V_{CEO}$  characteristic (Collector-emitter sustaining). The  $V_{CEO}$  characteristic shows a low-current "toe" that reduces to nothing as the level of leakage current increases. The graph also shows high and low leakage curves for the  $V_{CEO}$  characteristic.
+
+Figure 6: NPN transistor structure, circuit symbol and electrical characteristics. The top part shows a cross-section of an NPN transistor with layers N (Collector), P (Base), and N (Emitter). It includes a circuit diagram with a battery for V\_CBO and V\_CEO, and a circuit symbol. The bottom part is a graph of Collector current vs. Collector voltage, showing V\_CBO and V\_CEO characteristics with high and low leakage curves.
+
+Figure 6 – NPN transistor structure, circuit symbol and electrical characteristics
+
+Three-layer voltage limiters, usually made symmetrical in structure, give bidirectional voltage limiting; see Figure 7. The circuit symbol is formed from two of the unidirectional symbols of Figure 4, connected in series and opposition.
+
+This structure has similar breakdown characteristics in both voltage polarities and is termed bidirectional. These voltage limiting bidirectional diodes are available with breakdown voltages in the range of 5 V to 500 V and peak power ratings of 400 W to 5 kW. In restricted voltage ranges, higher power components of 30 kW are available.
+
+Fold-back diodes have the limitation that the degree of fold-back ( $V_{CBO}$  to  $V_{CEO}$  difference) reduces at lower voltages. Consequently the typical voltage range starts at 30 V and ends at 500 V. Fold-back diodes are available with current ratings up to 10 kA 8/20.
+
+![Figure 7: NPN voltage limiter structure, circuit symbol and electrical characteristics. The top part shows a schematic of an NPN structure connected to a voltage source, with layers labeled N, P, and N. To the right is a circuit symbol for a voltage limiter. The bottom part is a graph of Current versus Voltage, showing a fold-back clamping characteristic. The curve starts at the origin, goes into the third quadrant (reverse bias), then into the first quadrant (forward bias), reaching a peak labeled 'Reverse breakdown + forward conduction' before dropping back towards the origin, labeled 'Fold-back'. The axes are labeled 'Current' (vertical) and 'Voltage' (horizontal). A small code 'K.103(15)_F07' is in the bottom right corner.](71ab4df17511d75261da8d462d643b1a_img.jpg)
+
+Figure 7: NPN voltage limiter structure, circuit symbol and electrical characteristics. The top part shows a schematic of an NPN structure connected to a voltage source, with layers labeled N, P, and N. To the right is a circuit symbol for a voltage limiter. The bottom part is a graph of Current versus Voltage, showing a fold-back clamping characteristic. The curve starts at the origin, goes into the third quadrant (reverse bias), then into the first quadrant (forward bias), reaching a peak labeled 'Reverse breakdown + forward conduction' before dropping back towards the origin, labeled 'Fold-back'. The axes are labeled 'Current' (vertical) and 'Voltage' (horizontal). A small code 'K.103(15)\_F07' is in the bottom right corner.
+
+**Figure 7 – NPN voltage limiter structure, circuit symbol and electrical characteristics**
+
+Where the structure centre (P) layer is relatively thin, transistor action will occur resulting in a fold-back clamping characteristic like the  $V_{CEO}$  characteristic of Figure 6. When there is insignificant transistor action the clamping characteristic is the combination of the forward characteristic of Figure 2 and the  $V_{CBO}$  characteristic of Figure 6.
+
+Another variant of the three-layer structure is used for clamping applications of 10 V or less; see Figure 8. Here, the centre P-type layer is lightly doped and thin. When reverse voltage is applied the depletion layer extends completely through the centre layer and contacts the bottom N-type material layer. This action is called "punch-through" [b-King]. Products in the voltage range of 2.5 V to 5 V are commonly available in current ratings of 20 A 8/20 to 100 A 8/20.
+
+![Figure 8: NPN punch-through voltage limiter structure, circuit symbol and electrical characteristics.](ad29805cd4f64ad2828e14feb66de664_img.jpg)
+
+The figure illustrates the internal structure and electrical behavior of an NPN punch-through voltage limiter. At the top, a cross-section shows three layers: N, P, and N, with a depletion layer indicated in the P-layer. This structure is connected to a voltage source. To the right, a circuit symbol is shown, resembling two Zener diodes connected back-to-back. The bottom part is a graph of Current versus Voltage. In the first quadrant (positive voltage and current), the curve shows a sharp increase after a threshold. In the third quadrant (negative voltage and current), the curve shows a fold-back characteristic where the voltage increases to a peak and then snaps back to a lower value as current increases.
+
+K.103(15)\_F08
+
+Figure 8: NPN punch-through voltage limiter structure, circuit symbol and electrical characteristics.
+
+**Figure 8 – NPN punch-through voltage limiter structure, circuit symbol and electrical characteristics**
+
+The structure is unidirectional with only the negative polarity having the low-voltage fold-back characteristic. For this reason, this component often incorporates additional rectifier diodes as shown in Figure 9.
+
+![Figure 9: Punch-through arrays: unidirectional, bidirectional, single bridged and double bridged.](1a827b10290f33d4fec04d0e8ef7a897_img.jpg)
+
+This diagram shows four different circuit arrays of punch-through elements and diodes. From left to right, they represent: unidirectional (a punch-through element in series with a diode), bidirectional (two punch-through elements in series, back-to-back), single bridged (a punch-through element inside a four-diode bridge), and double bridged (a more complex bridge configuration). Each configuration shows how multiple punch-through elements are connected with diodes to achieve specific voltage clamping characteristics across the terminals.
+
+K.103(15)\_F09
+
+Figure 9: Punch-through arrays: unidirectional, bidirectional, single bridged and double bridged.
+
+**Figure 9 – Punch-through arrays: unidirectional, bidirectional, single bridged and double bridged**
+
+# 7 Characteristics
+
+A component electrical characteristic value is measured during a test that applies specified conditions. The key electrical characteristic points of clamping-type voltage limiters are shown in Figure 10. There is a great variation on the terminology used to describe these points. This clause explains the terminology used in this Recommendation and the significance of a parameter.
+
+![Figure 10: Key values on breakdown characteristic. A graph showing Current (Y-axis) versus Voltage (X-axis). The Y-axis has labels I_PPM, I_(BR), and I_R. The X-axis has labels V_RWM, V_(SB), V_(PT), V_(BR), and V_CM. The curve shows a sharp increase in current starting at V_(BR), with a dashed line indicating the breakdown region. The label K.103(15)_F10 is present at the bottom right of the graph.](1d529a819ad929684331c55eed6673bb_img.jpg)
+
+Figure 10: Key values on breakdown characteristic. A graph showing Current (Y-axis) versus Voltage (X-axis). The Y-axis has labels I\_PPM, I\_(BR), and I\_R. The X-axis has labels V\_RWM, V\_(SB), V\_(PT), V\_(BR), and V\_CM. The curve shows a sharp increase in current starting at V\_(BR), with a dashed line indicating the breakdown region. The label K.103(15)\_F10 is present at the bottom right of the graph.
+
+**Figure 10 – Key values on breakdown characteristic**
+
+## 7.1 Stand-off or maximum reverse working voltage, $V_{RWM}$
+
+Stand-off or maximum reverse working voltage ( $V_{RWM}$ ) is the peak value of a normal system working voltage that the component should be used with.
+
+### 7.1.1 Maximum reverse working voltage, $V_{RWM}$
+
+Maximum reverse working voltage ( $V_{RWM}$ ) is the highest instantaneous value of the reverse voltage, including all repetitive transient voltages, but excluding all non-repetitive transient voltages.
+
+### 7.1.2 Reverse current $I_R$
+
+The total conductive current flowing through the diode when specified reverse voltage is applied is called reverse current ( $I_R$ ). It may also commonly be called leakage current.
+
+The component current,  $I_R$ , is measured when the data sheet specified  $V_{RWM}$  voltage is applied. The data sheet should specify the maximum  $I_R$  value a tested component can have.
+
+A design consideration is the temperature inside the equipment where the component is used (microclimate). In general, the  $I_R$  of a PN junction doubles every  $10^{\circ}\text{C}$ . A temperature increase of  $40^{\circ}\text{K}$  to  $65^{\circ}\text{C}$  will increase  $I_R$  by  $2^4$  or 16 times. This may be a design consideration for system loading.
+
+The starting point for most designs would be to determine the peak service voltage in normal operation, then select a component with a  $V_{RWM}$  voltage equal to or greater than the service peak voltage.
+
+## 7.2 Breakdown voltage, $V_{(BR)}$
+
+This parameter is the voltage level where the components start to conduct significant current, and clipping of the applied voltage begins.
+
+### 7.2.1 Breakdown voltage $V_{(BR)}$
+
+Breakdown voltage ( $V_{(BR)}$ ) is the voltage in the region where breakdown occurs.
+
+### 7.2.2 Breakdown current $I_{(BR)}$
+
+Breakdown current ( $I_{(BR)}$ ) is the current in the region where breakdown occurs.
+
+The component breakdown voltage,  $V_{(BR)}$ , is measured when the data sheet specified  $I_{(BR)}$  current is applied. The data sheet should specify the maximum and minimum  $V_{(BR)}$  values a tested component can have.
+
+A design consideration is the temperature inside the equipment where the component is used (microclimate). The temperature coefficient of  $V_{(BR)}$  depends on the value of  $V_{(BR)}$ ; see Figure 11. In
+
+general, when  $V_{(BR)}$  is greater than 20 V a coefficient of 0.1%/°C can be assumed. A temperature change of 40 K will cause a 4% change in the  $V_{(BR)}$  value.
+
+Figure 4 shows that there is a considerable difference between the characteristics of 3.6 V, 8.2 V and 15 V breakdown diodes. The reason is that there are two breakdown mechanisms: Zener and avalanche. The 3.6 V diode has Zener breakdown and the characteristic has a high slope resistance. The 15 V diode has avalanche breakdown and the characteristic has a low slope resistance. The 8.2 V diode has a mixture of the two types of breakdown. The initial conduction is due to Zener breakdown, but as the current rises and the voltage increases, the breakdown becomes avalanche. The temperature coefficient characteristic, Figure 11, shows a similar effect. Below 6 V the Zener breakdown negative temperature coefficient predominates and above 6 V the avalanche breakdown positive temperature coefficient predominates. The temperature coefficient is dependent on the value of  $I_{(BR)}$  used for the  $V_{(BR)}$  measurement. Higher values of  $I_{(BR)}$  make the curve more negative. For example, increasing the test current from 5 mA to 40 mA on a 10 V component decreases the temperature coefficient from 0.05%/°C to 0.03%/°C.
+
+![Figure 11: A graph showing the Temperature coefficient (in %/°C) versus Breakdown voltage, V(BR) (in V) on a logarithmic scale. The y-axis ranges from -0.10 to 0.10 in increments of 0.02. The x-axis ranges from 1 to 100 in powers of 10. The curve starts at approximately (3.6, -0.07), crosses the zero line at about 6 V, and rises to approximately (100, 0.09).](b6750d26d3dd287a4a4d49b3670a44bd_img.jpg)
+
+| Breakdown voltage, $V_{(BR)}$ (V) | Temperature coefficient (%/°C) |
+|-----------------------------------|--------------------------------|
+| 3.6                               | -0.07                          |
+| 6                                 | 0.00                           |
+| 10                                | 0.05                           |
+| 20                                | 0.07                           |
+| 50                                | 0.085                          |
+| 100                               | 0.09                           |
+
+Figure 11: A graph showing the Temperature coefficient (in %/°C) versus Breakdown voltage, V(BR) (in V) on a logarithmic scale. The y-axis ranges from -0.10 to 0.10 in increments of 0.02. The x-axis ranges from 1 to 100 in powers of 10. The curve starts at approximately (3.6, -0.07), crosses the zero line at about 6 V, and rises to approximately (100, 0.09).
+
+Figure 11 – Temperature coefficient of breakdown voltage  $V_{(BR)}$  example
+
+Historically, the Zener breakdown phenomenon was discovered first by C. Zener in 1934 [b-Zener]. It was not until 1953 that it was realised that there was a second form of breakdown phenomenon, avalanche breakdown also existed, as discovered by K.G. McKay and K.B. McAfee [b-McKay]. Due to the longer usage of the terminology, all breakdown diodes are often incorrectly called "Zener diodes".
+
+## 7.3 Clamping voltage, $V_C$
+
+The clamping voltage ( $V_C$ ) parameter is the let-through (clamping) voltage of the component during the conduction of a current impulse having a peak pulse current ( $I_{PP}$ ) and specified waveshape. The highest (maximum) value of clamping voltage ( $V_{CM}$ ) occurs at the rated peak (maximum) impulse current ( $I_{PPM}$ ).
+
+### 7.3.1 Maximum clamping voltage, $V_{CM}$
+
+Maximum clamping voltage ( $V_{CM}$ ) is the peak voltage developed when conducting the rated ( $I_{PPM}$ ) current waveform.
+
+### 7.3.2 Maximum peak pulse current, $I_{PPM}$
+
+Maximum peak pulse current ( $I_{PPM}$ ) is the rated value of maximum impulse current that may be applied.
+
+The component  $V_{CM}$  is measured when the data sheet specified  $I_{PPM}$  current is applied. The data sheet should specify the highest  $V_{CM}$  value a tested component can have.
+
+The time at which  $V_{CM}$  occurs will not be at the time at which the impulse reaches  $I_{PPM}$ ; see Figure 12.
+
+![Figure 12: Waveforms of current (I_pp) and voltage (V_c) over time. The current waveform (I_pp) is a sharp, high peak reaching I_PPM around 10 units of time. The voltage waveform (V_c) is a broader, lower peak reaching V_CM around 15 units of time. The current waveform decays faster than the voltage waveform. The x-axis is labeled from 0 to 50. A small label K.103(15)_F12 is present at the bottom right of the graph.](3468bcffa38de23cef94bfb460ccb301_img.jpg)
+
+Figure 12: Waveforms of current (I\_pp) and voltage (V\_c) over time. The current waveform (I\_pp) is a sharp, high peak reaching I\_PPM around 10 units of time. The voltage waveform (V\_c) is a broader, lower peak reaching V\_CM around 15 units of time. The current waveform decays faster than the voltage waveform. The x-axis is labeled from 0 to 50. A small label K.103(15)\_F12 is present at the bottom right of the graph.
+
+Figure 12 –  $V_c$  and  $I_{pp}$  waveforms
+
+## 7.4 Punch-through voltage $V_{(PT)}$
+
+The current level at which a fold-back component reaches the punch-through voltage ( $V_{(PT)}$ ) may not be well defined; see Figure 10. For this reason, the best measurement approach is to apply a low-level current ramp and measure the peak voltage. This voltage is equivalent to  $V_{(BR)}$  in a normal breakdown characteristic.
+
+### 7.4.1 Punch-through voltage, $V_{(PT)}$
+
+Punch-through voltage ( $V_{(PT)}$ ) is the first voltage peak in the low-level current voltage characteristic.
+
+## 7.5 Snap back voltage $V_{(SB)}$
+
+The current level at which a fold-back component breakdown voltage is at its lowest value (snapback voltage ( $V_{(SB)}$ )) may not be well defined; see Figure 10. For this reason, the best measurement approach is to apply a low-level current ramp and measure the minimum breakdown voltage. If the service being protected has a DC supply it is important that the snapback voltage is higher than the DC supply voltage to avoid the possibility of latch-up at the snapback voltage.
+
+### 7.5.1 snapback voltage, $V_{(SB)}$
+
+Snapback voltage ( $V_{(SB)}$ ) is the lowest voltage in the breakdown characteristic after the punch-through occurs.
+
+## 7.6 Forward biased PN junction voltage, $V_F$
+
+The main parameter for a forward biased PN junction is the forward voltage ( $V_F$ ) at  $I_{PPM}$ .
+
+### 7.6.1 Forward voltage, $V_F$
+
+Forward voltage ( $V_F$ ) [b-IEC 60747-2] is the voltage across the terminals which results from the flow of current in the forward direction.
+
+The forward voltage varies with temperature, Figure 13. The typical forward voltage temperature coefficient is  $-2 \text{ mV}/^\circ\text{C}$ , falling to about  $-1.3 \text{ mV}/^\circ\text{C}$  at high currents.
+
+![Figure 13: A semi-logarithmic plot showing Current I_F (A) versus Voltage V_F (V) at three temperatures: 100 °C (red dashed line), 25 °C (black solid line), and -55 °C (green dashed line). The y-axis ranges from 10 µA to 10 A, and the x-axis ranges from 0.0 V to 1.5 V. The curves show that for a given current, the forward voltage decreases as temperature increases. The 100 °C curve is the leftmost, followed by the 25 °C curve, and then the -55 °C curve. All curves show a sharp increase in current as voltage increases, eventually reaching a plateau at high currents.](9260ae281f6b6470331f4a0f82dbc2b1_img.jpg)
+
+Figure 13 is a semi-logarithmic plot showing the relationship between forward current ( $I_F$ ) and forward voltage ( $V_F$ ) for a diode at three different temperatures. The y-axis represents current in Amperes (A) on a logarithmic scale from  $10 \mu\text{A}$  to  $10 \text{ A}$ . The x-axis represents voltage in Volts (V) on a linear scale from  $0.0 \text{ V}$  to  $1.5 \text{ V}$ . Three curves are plotted: a red dashed line for  $100^\circ\text{C}$ , a black solid line for  $25^\circ\text{C}$ , and a green dashed line for  $-55^\circ\text{C}$ . The curves show that for a given current, the forward voltage decreases as temperature increases. The 100 °C curve is the leftmost, followed by the 25 °C curve, and then the -55 °C curve. All curves show a sharp increase in current as voltage increases, eventually reaching a plateau at high currents.
+
+Figure 13: A semi-logarithmic plot showing Current I\_F (A) versus Voltage V\_F (V) at three temperatures: 100 °C (red dashed line), 25 °C (black solid line), and -55 °C (green dashed line). The y-axis ranges from 10 µA to 10 A, and the x-axis ranges from 0.0 V to 1.5 V. The curves show that for a given current, the forward voltage decreases as temperature increases. The 100 °C curve is the leftmost, followed by the 25 °C curve, and then the -55 °C curve. All curves show a sharp increase in current as voltage increases, eventually reaching a plateau at high currents.
+
+Figure 13 –  $I_F$  vs.  $V_F$  at three temperatures
+
+At fast rates of current rise it can take some time for the PN junction to establish full conduction. This results in a voltage spike at the beginning of conduction, Figure 14. If the forward voltage characteristic is being used to limit voltage to specific levels under impulse conditions the component  $V_{\text{FRM}}$  should be specified. For example, some samples of the commonly used 1N4000 series rectifiers were found to have  $V_{\text{FRM}}$  values of over  $100 \text{ V}$  when tested with an 8/20 impulse current.
+
+### 7.6.2 Forward recovery voltage, $V_{\text{FR}}$
+
+Forward recovery voltage ( $V_{\text{FR}}$ ) [b-IEC 60747-2] represents the varying voltage occurring during the forward recovery time after instantaneous switching from zero or a specified reverse voltage to a specified forward current.
+
+![Figure 14: Forward recovery voltage vs. time. The top graph shows voltage (v) on the y-axis versus time (t in μs) on the x-axis. The voltage curve rises sharply to a peak labeled V_FRM and then decays exponentially toward a steady-state forward voltage V_F. The bottom graph shows current (i) on the y-axis versus time (t in μs) on the x-axis. The current curve rises with a constant slope labeled dI_F/dt until it reaches a steady-state forward current I_F. Both graphs share the same time axis. A reference label K.103(15)_F14 is located at the bottom right of the figure.](5ed9189841659dfb01f809b8e3b21f74_img.jpg)
+
+Figure 14: Forward recovery voltage vs. time. The top graph shows voltage (v) on the y-axis versus time (t in μs) on the x-axis. The voltage curve rises sharply to a peak labeled V\_FRM and then decays exponentially toward a steady-state forward voltage V\_F. The bottom graph shows current (i) on the y-axis versus time (t in μs) on the x-axis. The current curve rises with a constant slope labeled dI\_F/dt until it reaches a steady-state forward current I\_F. Both graphs share the same time axis. A reference label K.103(15)\_F14 is located at the bottom right of the figure.
+
+**Figure 14 – Forward recovery voltage vs. time**
+
+## 7.7 Junction capacitance, $C_J$
+
+The capacitance of a reverse biased PN junction ( $C_J$ ) decreases with increasing breakdown voltage and the applied voltage. The signal amplitude used to measure capacitance is typically 50 mV rms. This low level is necessary to avoid rectification by the forward characteristic of unidirectional breakdown diodes.
+
+Figure 15 shows how the capacitance of a 1500 W unidirectional diode decreases with increasing  $V_{(BR)}$  and applied DC bias. The dotted 100 pF line is for the same PN structure, but with a series diode to lower the capacitance (extreme left configuration of Figure 5). Low-voltage punch-through components in diode arrays can have capacitance values approaching 10 pF.
+
+![Figure 15: Capacitance variation with V_(BR), voltage bias and configuration. This is a log-linear plot. The vertical axis represents Junction capacitance, C_J in nF, ranging from 0.1 to 10 on a logarithmic scale. The horizontal axis represents Breakdown voltage, V_(BR) - V, ranging from 5 to 100 on a linear scale. Three data series are plotted: 1) 'Bias = 0' (solid black line) starting at ~10 nF for 5V and decreasing to ~1.5 nF at 100V. 2) 'Bias = V_RWM' (solid grey line) starting at ~5 nF for 5V and decreasing to ~0.4 nF at 100V. 3) 'Bias = 0 with series diode' (dotted blue line) which is a horizontal line at exactly 0.1 nF (100 pF) across the entire voltage range. A reference label K.103(15)_F15 is at the bottom right.](723827e0738d2743c3b3423760a5c48e_img.jpg)
+
+Figure 15: Capacitance variation with V\_(BR), voltage bias and configuration. This is a log-linear plot. The vertical axis represents Junction capacitance, C\_J in nF, ranging from 0.1 to 10 on a logarithmic scale. The horizontal axis represents Breakdown voltage, V\_(BR) - V, ranging from 5 to 100 on a linear scale. Three data series are plotted: 1) 'Bias = 0' (solid black line) starting at ~10 nF for 5V and decreasing to ~1.5 nF at 100V. 2) 'Bias = V\_RWM' (solid grey line) starting at ~5 nF for 5V and decreasing to ~0.4 nF at 100V. 3) 'Bias = 0 with series diode' (dotted blue line) which is a horizontal line at exactly 0.1 nF (100 pF) across the entire voltage range. A reference label K.103(15)\_F15 is at the bottom right.
+
+**Figure 15 – Capacitance variation with  $V_{(BR)}$ , voltage bias and configuration**
+
+The component capacitance is a problem in high frequency systems as it represents a shunt to the signal and creates signal distortion due to the capacitance variation with signal voltage and DC bias. Bidirectional diodes are two unidirectional structures in series. As a result, the zero bias capacitance of a bidirectional diode will normally be about 50% of a capacitance of a unidirectional diode.
+
+A three-layer structure with 0 V bias has two PN junctions each with its own depletion layer which forms two capacitors in series; see Figure 16. Applying a DC voltage bias causes one junction to forward bias and the other to reverse bias. As the voltage increases the depletion layer width of the reverse biased junction increases, thus further separating the plates of the depletion layer capacitor. As the plates move apart the capacitance decreases. The capacitance curve shown in Figure 16 peaks at 150 pF and falls to 80 pF with a bias of 10 V.
+
+![Figure 16: Bidirectional NPN structure junction capacitance graph and diagrams.](9a19da4f7fccb96a934411c0bb5a386d_img.jpg)
+
+Figure 16 shows a graph of junction capacitance ( $C_j$  in pF) versus applied DC voltage (V). The curve is bell-shaped, peaking at approximately 150 pF at 0 V bias and decreasing symmetrically as the voltage increases or decreases. At 10 V and -10 V, the capacitance is approximately 80 pF. At 20 V and -20 V, it falls to about 65-70 pF. The graph includes schematics of the bidirectional diode structure at different bias points. At 0 V, two junctions D1 and D2 are shown with equal depletion widths. At positive bias, D1 is forward-biased (narrower) and D2 is reverse-biased (wider). The formula  $C = \epsilon A/d$  is provided. A note states: "Bidirectional devices have two blocking junctions, D1 and D2, one for each polarity."
+
+| Applied DC voltage - V (V) | $C_j$ - capacitance - pF (pF) |
+|----------------------------|-------------------------------|
+| -20                        | ~65                           |
+| -10                        | ~85                           |
+| 0                          | 150                           |
+| 10                         | 80                            |
+| 20                         | ~65                           |
+
+Figure 16: Bidirectional NPN structure junction capacitance graph and diagrams.
+
+**Figure 16 – Bidirectional NPN structure junction capacitance**
+
+If a sinewave voltage is applied to the component represented by Figure 16, the current drawn will be given by  $i = C_j dv/dt$ . Figure 17 shows the currents for 1 V and 5 V signals. As the voltage passes through zero the capacitance reaches a maximum value and  $dv/dt$  is at its fastest rate. With a large 5 V signal, a triangular current waveshape is created due to the zero crossing effect. The triangular current waveshape has a large harmonic spectrum as shown in Figure 17. Multifrequency signals will suffer intermodulation distortion.
+
+![Figure 17: Non-linear capacitance signal distortion plots.](0add961f6fd54a7ae5391d00c7e58f3c_img.jpg)
+
+Figure 17 contains three sub-plots. The first plot, labeled "±1 V peak voltage sinewave", shows a sinusoidal voltage (black line, peak amplitude 1) and a corresponding current (red line, peak amplitude ~150). The second plot, labeled "±5 V peak voltage sinewave", shows a sinusoidal voltage (black line, peak amplitude 5) and a current (red line, peak amplitude ~150) that has a distinct triangular shape near the zero crossings. The third plot, labeled "'5 V' current frequency domain plot", is a bar chart showing the magnitude of harmonics. The fundamental frequency (at 10) has a magnitude of 1.0, with significant odd harmonics appearing at higher frequencies (e.g., 3rd harmonic at 30).
+
+Figure 17: Non-linear capacitance signal distortion plots.
+
+**Figure 17 – Non-linear capacitance signal distortion**
+
+## **7.8 Package inductance**
+
+Fast rates of current rise will generate voltage spikes from the component package. Axial leaded components may have package inductance values of 10 nH and surface-mount components may be in the 4 nH ranges. Often the printed circuit wiring will contribute even larger values of inductance. A 20 mm long printed wiring trace could have 25 nH of inductance. A rising current of 100 A/μs would generate a spike of 2.5 V across the trace. In-line package designs and connections considerably reduce these inductive voltage spikes; see Figure 18. The left hand circuit shows how the fast rising current conducted by the breakdown diode creates inductive voltage spikes in the connecting wires; these voltage spikes are also applied to the protected load. The right hand circuit routes the wiring to the diode first then on to the protected load. The load does not have the inductive spike voltages applied to it.
+
+![Figure 18: Reducing inductive spikes by inline connection. The diagram shows two circuit configurations for a transient voltage suppressor (TVS) diode protecting a load. The left circuit shows the TVS diode connected in parallel with the load, but with significant lead/trace inductance (represented by coils) in the path. A fast-rising current pulse I_PP causes voltage spikes across these inductances, which are then seen by the load. The right circuit shows an 'in-line' connection where the input current goes directly to the TVS diode terminals first, and the load is connected to those same terminals. This configuration ensures that the inductive spikes from the input wiring are shunted by the diode and not applied to the load.](d734a6ea1b381280f043fcf70391b6db_img.jpg)
+
+Figure 18: Reducing inductive spikes by inline connection. The diagram shows two circuit configurations for a transient voltage suppressor (TVS) diode protecting a load. The left circuit shows the TVS diode connected in parallel with the load, but with significant lead/trace inductance (represented by coils) in the path. A fast-rising current pulse I\_PP causes voltage spikes across these inductances, which are then seen by the load. The right circuit shows an 'in-line' connection where the input current goes directly to the TVS diode terminals first, and the load is connected to those same terminals. This configuration ensures that the inductive spikes from the input wiring are shunted by the diode and not applied to the load.
+
+**Figure 18 – Reducing inductive spikes by inline connection**
+
+# **8 Ratings**
+
+A component electrical rating is verified by applying the rated value and the test check for degradation. Degradation is evaluated by measuring specified electrical characteristic parameters, which should remain within specified limits.
+
+## **8.1 Peak pulse current, $I_{PP}$**
+
+The maximum peak pulse current ( $I_{PPM}$ ) and its specified waveshape is the manufacturers' rating that should not be exceeded in service or testing. For components intended to mitigate surges caused by lightning an 8/20 waveshape is usually specified.
+
+### **8.1.1 Peak pulse current, $I_{PP}$**
+
+Peak pulse current ( $I_{PP}$ ) is the conducted impulse current of a specified amplitude and waveshape used to determine the clamping voltage  $V_C$ .
+
+### **8.1.2 Maximum peak pulse current, $I_{PPM}$**
+
+Maximum peak pulse current ( $I_{PPM}$ ) is the rated maximum value of peak pulse current  $I_{PP}$  that may be applied without causing component failure.
+
+A given component series will use the same sized chip, processed appropriately to give the required voltage. The chip will have a certain energy capability; the energy developed under  $I_{PP}$  conditions will be related to the product of voltage and current. Low-voltage parts will have the highest current rating and high-voltage parts, the lowest current rating; see Figure 19.
+
+![Figure 19: Example plot of I_PPM vs. V_WRM. The graph is a log-log plot showing Maximum peak pulse current, I_PPM - A (Y-axis) versus Maximum reverse working voltage, V_WRM - V (X-axis). The Y-axis ranges from 10 to 100, and the X-axis ranges from 10 to 100. A downward-sloping curve is shown. A small label 'K.103(15)_F19' is present in the bottom right corner of the plot area.](9ce50bc10864dc86e1cdee4be08f1897_img.jpg)
+
+Figure 19: Example plot of I\_PPM vs. V\_WRM. The graph is a log-log plot showing Maximum peak pulse current, I\_PPM - A (Y-axis) versus Maximum reverse working voltage, V\_WRM - V (X-axis). The Y-axis ranges from 10 to 100, and the X-axis ranges from 10 to 100. A downward-sloping curve is shown. A small label 'K.103(15)\_F19' is present in the bottom right corner of the plot area.
+
+**Figure 19 – Example plot of  $I_{PPM}$  vs.  $V_{WRM}$**
+
+When operated correctly, breakdown diodes do not have a significant wear-out mechanism. However, when the rated value is exceeded, the diode will either fail instantly or have a short impulse life. In 1977, National Aeronautics and Space Administration (NASA) reported on an impulse durability program for avalanche diodes; see [b-Clark]. The metrics were:
+
+- 12 500 000 pulses applied to the avalanche breakdown diodes;
+- 6.8 V, 33 V, 91 V and 190 V parts tested;
+- 10/1000 impulse levels of 25%, 50%, 75% and 100% rated current.
+
+An example result is shown in Figure 20. The result shows that the impulse durability of a breakdown diode depends on how a manufacturer rates the component. At 75%  $I_{PPM}$  and below, testing did not produce any significant number of failures. A 500 impulse life was predicted if 190 V diodes were tested at 125%  $I_{PPM}$  and instant failure at 150%  $I_{PPM}$ .
+
+![Figure 20: A graph showing the relationship between the number of impulses before failure (x-axis, 0 to 6000) and the percentage of rated peak pulse current (y-axis, 0 to 150). The curve starts at 150% at 0 impulses and decreases, leveling off around 85% after approximately 2000 impulses. A text box indicates that data was gathered on 2,164,000 component impulses at 25%, 50%, and 75% I_PPM without significant failures. A legend indicates the solid line is 'Calculated from data' and the dashed line is 'Extrapolated'. A label 'Mean value' points to the curve at approximately 2500 impulses. The code K.103(15)_F20 is shown in the bottom right.](645bea0b27d63e4a9a300af5793ae7d2_img.jpg)
+
+Data on 2.164.000 component impulses was gathered at 25 %  
+50 % and 75 %  $I_{\text{PPM}}$  without a significant number of failures to  
+calculate a failure rate.
+
+Mean value
+
+—— Calculated from data      - - - - Extrapolated
+
+K.103(15)\_F20
+
+Figure 20: A graph showing the relationship between the number of impulses before failure (x-axis, 0 to 6000) and the percentage of rated peak pulse current (y-axis, 0 to 150). The curve starts at 150% at 0 impulses and decreases, leveling off around 85% after approximately 2000 impulses. A text box indicates that data was gathered on 2,164,000 component impulses at 25%, 50%, and 75% I\_PPM without significant failures. A legend indicates the solid line is 'Calculated from data' and the dashed line is 'Extrapolated'. A label 'Mean value' points to the curve at approximately 2500 impulses. The code K.103(15)\_F20 is shown in the bottom right.
+
+**Figure 20 – 190 V diode per cent of rated peak pulse current vs. mean peak pulses before failure**
+
+## 8.2 Maximum peak pulse power, $P_{\text{PPM}}$
+
+Figure 12 shows that the impulse peak current and the component maximum voltage may not occur at the same time. The product of the peak current and maximum voltage is called peak pulse power. It is a fictive quantity in so much as the current and voltage may not be coincident in time. Nonetheless, maximum peak pulse power ( $P_{\text{PPM}}$ ), is a widely used parameter.
+
+Manufacturers often supply component  $P_{\text{PPM}}$  versus pulse width curves for impulse, half sine wave and rectangular pulse waveshapes. For impulse waveshapes of time to half amplitude,  $t_D$   $\mu\text{s}$ , the relationship approximates to:
+
+$$y = a(t_D)^{-0.45}$$
+
+where:
+
+$y$  is the ratio of  $P_{\text{PPM}}$  at  $t_D$  to the  $P_{\text{PPM}}$  at specified component  $t_D$  waveshape, usually 8/20 or 10/1000  $a$  is a constant, 3.8 when the specified component  $t_D$  waveshape is 8/20 and 22 when the specified component  $t_D$  waveshape is 10/1000.
+
+For example, if a component has a specified  $t_D$  waveshape of 10/1000 and the  $P_{\text{PPM}}$  value at 8/20 is required,  $y = 22(20)^{-0.45} = 5.7$ . A 500 W  $P_{\text{PPM}}$  10/1000 component should have an 8/20 rating in the  $5.7 \times 500 = 2850$  W region. Working out what this means in terms of  $V_{\text{CM}}$  and  $I_{\text{PPM}}$  requires the manufacture to supply a relationship curve of these two parameters.
+
+## 8.3 Power dissipation, $P_D$
+
+The rated steady state power dissipation ( $P_D$ ) maintains the junction temperature at the highest acceptable value. Values of 175°C or 150°C are typical. If the component is operated in an ambient higher than 25°C, the maximum allowable power loss must be reduced to maintain the same junction temperature. For example, if the maximum junction temperature was 175°C and the ambient was 75°C the maximum power loss becomes  $P_D \times (175-75)/(175-25) = 0.67P_D$ . The same derating factor could be applied to the  $P_{\text{PPM}}$  rating as well.
+
+# 9 Application examples
+
+The outline designs presented in this clause are conceptual. The circuit descriptions note some design considerations, but are not rigorous design procedures.
+
+## 9.1 Series connection
+
+The series connection of several breakdown diodes creates a protective function of higher maximum working voltage,  $V_{RWM}$  voltage than the individual components or a higher maximum peak pulse current,  $I_{PPM}$ , than a single component with the function voltage or both; see Figure 21.
+
+In the following example all the components used in the series string will be of the same type. The series string will have an overall maximum reverse working voltage of  $nV_{RWM}$ , where  $n$  is the number of components and  $V_{RWM}$  is the individual component maximum reverse working voltage. The  $I_{PPM}$  of the series string will be the same as the individual string component  $I_{PPM}$ . Figure 19 shows that as the value of  $V_{RWM}$  increases the value of  $I_{PPM}$  decreases.
+
+A single component having a  $V_{RWM}$  of 170 V might have an  $I_{PPM}$  of 5.5 A, 8/20. Using several lower voltage components in series to make up the same 170 V overall  $V_{RWM}$  will give a protective function of higher  $I_{PPM}$ ; see Figure 22. Roughly the  $I_{PPM}$  of the series string increases by the number of components used for a fixed overall value of  $V_{RWM}$ . A disadvantage of series connection is that the overall series inductance of the protective function is higher than an individual component.
+
+![Figure 21: Multiple component series and parallel connection. The diagram shows two circuit configurations. On the left, a series connection of two diodes labeled D1 and Dn. On the right, a parallel connection of two diodes labeled D1 and Dn. Both configurations are connected to terminals at the top and bottom. The label K.103(15)_F21 is present at the bottom right of the diagram.](392a79ccd95e682ccd08f35ab2e64144_img.jpg)
+
+Figure 21: Multiple component series and parallel connection. The diagram shows two circuit configurations. On the left, a series connection of two diodes labeled D1 and Dn. On the right, a parallel connection of two diodes labeled D1 and Dn. Both configurations are connected to terminals at the top and bottom. The label K.103(15)\_F21 is present at the bottom right of the diagram.
+
+Figure 21 – Multiple component series and parallel connection
+
+![Figure 22: I_PPM of series string versus number of components n. This is a line graph showing the relationship between the number of components (n) and the maximum peak pulse current (I_PPM) in Amperes. The x-axis is labeled 'Number of components, n' and ranges from 0 to 20. The y-axis is labeled 'Maximum peak pulse current, I_PPM - A' and is a logarithmic scale with major ticks at 1, 10, and 100. The curve starts at approximately (1, 5) and increases, leveling off towards 100 A as n approaches 20. The label K.103(15)_F22 is present at the bottom right of the graph.](cdba53bb2fb4d459f37515ee7fab3418_img.jpg)
+
+Figure 22: I\_PPM of series string versus number of components n. This is a line graph showing the relationship between the number of components (n) and the maximum peak pulse current (I\_PPM) in Amperes. The x-axis is labeled 'Number of components, n' and ranges from 0 to 20. The y-axis is labeled 'Maximum peak pulse current, I\_PPM - A' and is a logarithmic scale with major ticks at 1, 10, and 100. The curve starts at approximately (1, 5) and increases, leveling off towards 100 A as n approaches 20. The label K.103(15)\_F22 is present at the bottom right of the graph.
+
+Figure 22 –  $I_{PPM}$  of series string versus number of components  $n$
+
+Lower voltage components have higher  $V_{CM}/V_{RWM}$  ratios. Thus with more components used in the string, not only does the  $I_{PPM}$  increase, but so does the  $V_{CM}$ . This might be undesirable. To have a consistent value of  $V_{CM}$ , the series string  $I_{PPM}$  value needs to be derated.
+
+Some manufacturers provide curves of  $V_C - V_{(BR)}$  against  $I_{PP}$  and from these the appropriate value of  $I_{PP}$  for a given  $V_{CM}$  can be calculated. Without that information an estimate can be made of the  $I_{PP}$  value from the component  $V_{CM}$ ,  $V_{(BR)}$  and  $V_{RWM}$ . The breakdown characteristic resistance,  $R_{(BR)}$ , is approximated to  $R_{(BR)} = (V_{CM} - V_{(BR)})/I_{PPM}$ . At any current,  $I_{PP}$ , the value of  $V_C$  is  $I_{PP} R_{(BR)} + V_{(BR)}$ . The reduction ratio,  $I_{PP}/I_{PPM}$ , is  $(V_{CX} - V_{(BR)})/(V_{CM} - V_{(BR)})$ , where  $V_{CX}$  is the desired value of clamping voltage. Figure 23 shows a smoothed curve of the results obtained for a 1500 W  $P_{PPM}$  component.
+
+![Figure 23: A line graph showing the reduction factor, I_PP/I_PPM, versus the number of series string components, n. The y-axis ranges from 0.80 to 1.00 with major grid lines every 0.05 units. The x-axis ranges from 0 to 20 with major grid lines every 5 units. A single straight line starts at (0, 1.00) and decreases linearly to approximately (20, 0.85). The label 'K.103(15)_F23' is in the bottom right corner of the graph area.](391ab9e5616ba6311161af4d7a93422b_img.jpg)
+
+| Number of components, n | Reduction factor, $I_{PP}/I_{PPM}$ |
+|-------------------------|------------------------------------|
+| 0                       | 1.00                               |
+| 5                       | 0.95                               |
+| 10                      | 0.90                               |
+| 15                      | 0.875                              |
+| 20                      | 0.85                               |
+
+Figure 23: A line graph showing the reduction factor, I\_PP/I\_PPM, versus the number of series string components, n. The y-axis ranges from 0.80 to 1.00 with major grid lines every 0.05 units. The x-axis ranges from 0 to 20 with major grid lines every 5 units. A single straight line starts at (0, 1.00) and decreases linearly to approximately (20, 0.85). The label 'K.103(15)\_F23' is in the bottom right corner of the graph area.
+
+Figure 23 –  $I_{PP}/I_{PPM}$  current reduction factor versus number of series string components, n
+
+## 9.2 Parallel connection
+
+Paralleling several components or series component strings never realizes the sum of the  $I_{PPM}$  values. Current sharing cannot be guaranteed. Some manufacturers select and match the components used, but that component match can never be exact, so some derating of the ideal  $I_{PPM}$  is necessary. One manufacturer recommends measuring diode  $V_C$  values under moderate (e.g., 1 A) pulse conditions then sorting the diodes into 1% voltage tolerance groups.
+
+One compensating factor for avalanche breakdown diodes is the positive temperature coefficient of voltage. A lower voltage component (or string) will take more current and hence have a higher power loss. This heating raises the junction temperature, which in turn increases the  $V_C$  value. The increased  $V_C$  value causes some of the conducted current to divert to the previously higher  $V_C$  paths.
+
+## 9.3 DC supply protection
+
+Breakdown diodes, both unidirectional and bidirectional can protect DC supplies from positive and negative transients and provide fault protection. Figure 24 shows the basic arrangement. The breakdown diode,  $V_{RWM}$ , will be selected to be greater than the highest DC supply voltage value. Positive transients will be limited to the diode  $V_C$  value at the available transient current. Negative transients will be limited to the diode  $V_F$  value at the available transient current.
+
+In some designs the diode will be used as a shorting mechanism if the power supply develops a fault and outputs an excessive voltage. If the faulty power supply causes DC conduction of the diode it will overheat and initially go short, thus terminating the excessive voltage period. This feature only works if the faulty power supply has a limited current and does not cause the failed diode to fuse open. Some manufacturers will provide fusing (opening) information on their diode construction.
+
+Example clearing (opening) times published for a 1500 W axial component have been given as 400 A at 0.1 s, 90 A at 10 s and 30 A at 1000 s. With this information a suitable series fuse element can be built into the power supply to operate before the diode fuses open.
+
+![Figure 24: Basic DC supply protection circuit diagram.](d17aa1fcc3b86503ad1dd0717a6c34c2_img.jpg)
+
+The diagram shows a DC supply with a positive (+) and negative (-) rail. A diode is connected in parallel across the supply rails. The cathode of the diode is connected to the positive rail, and the anode is connected to the negative rail. Below the diagram is the identifier K.103(15)\_F24.
+
+Figure 24: Basic DC supply protection circuit diagram.
+
+**Figure 24 – Basic DC supply protection**
+
+### 9.3.1 Automotive load dump
+
+An automotive load dump is the term for the condition when the alternator is charging the battery and the battery becomes disconnected. The resulting alternator energy release results in a voltage spike of about 100 V with a duration in the 300 ms region. Besides making sure that the selected diode, D1, can absorb the load dump energy, automotive load dump protection design has some other considerations. Jumpstarting a car by connecting an external 24 V supply requires that the diode  $V_{RWM}$  is greater than 24 V. The possibility of a reverse connected battery causing diode forward conduction can be avoided by connecting a series diode, D2. Finally, to avoid reverse polarity voltage spikes breaking down the series diode, D2, a bidirectional breakdown diode, D3, can be added across the series diode, D2. Negative voltage spikes will be limited by the conduction of diodes D3 and D1. This circuit arrangement is shown in Figure 25.
+
+![Figure 25: Automotive load dump protection circuit diagram.](759c7d62402f0b4651ddce292be5bdef_img.jpg)
+
+The diagram illustrates an automotive load dump protection circuit. On the left, an 'Alternator' is connected to positive (+) and negative (-) rails. In the positive rail, a series diode D2 is placed. Connected in parallel across diode D2 is a bidirectional breakdown diode D3. Following these, a breakdown diode D1 is connected in parallel across the positive and negative rails, with its cathode on the positive rail. To the right of D1, the output is labeled 'Protected electronics'. Below the diagram is the identifier K.103(15)\_F25.
+
+Figure 25: Automotive load dump protection circuit diagram.
+
+**Figure 25 – Automotive load dump protection**
+
+### 9.3.2 Power over Ethernet (PoE)
+
+In this remote powering system, the power sourcing equipment (PSE) uses the Ethernet cabling to feed a safety extra low voltage (SELV) to the powered device (PD). Traditionally both the PSE and PD contain a 58 V breakdown diode for protection. Figure 26 shows the overvoltage protection of the PSE power feed and the PD power feed recovery circuit. The PSE protection consists of breakdown diode D10 and capacitor C2. The power feed is delivered to the PD by combinations of the four Ethernet twisted pairs, which can operate in mode A or B or both. Diode bridges D1 through D4 and D5 through D8 extract the power feed from the cable connections with the appropriate voltage polarity for the PD power controller. The PSE protection consists of breakdown diode D9 and capacitor C1. The diodes used should be sized for the surge resistibility requirements of the standards to be complied with.
+
+![Figure 26: PSE power feed and PD feed recovery circuit diagram. The left side shows a PSE power source connected to a breakdown diode D10 and a capacitor C2 (100 nF) in parallel, labeled 'To PSE RJ 45 and magnetics'. The right side shows a PD supply connected to a bridge rectifier (diodes D1 to D8) and a breakdown diode D9 in parallel with a capacitor C1 (100 nF), labeled 'To PD RJ 45 and magnetics' and 'PD supply'. The diagram is labeled K.103(15)_F26.](69b7bd65e85cdef6fdd7fb0a8194257c_img.jpg)
+
+Figure 26: PSE power feed and PD feed recovery circuit diagram. The left side shows a PSE power source connected to a breakdown diode D10 and a capacitor C2 (100 nF) in parallel, labeled 'To PSE RJ 45 and magnetics'. The right side shows a PD supply connected to a bridge rectifier (diodes D1 to D8) and a breakdown diode D9 in parallel with a capacitor C1 (100 nF), labeled 'To PD RJ 45 and magnetics' and 'PD supply'. The diagram is labeled K.103(15)\_F26.
+
+**Figure 26 – PSE power feed and PD feed recovery**
+
+## 9.4 Power frequency protection
+
+Bidirectional breakdown diodes can protect alternating current (AC) supplies from positive and negative transients. Some AC surge protective devices, SPDs, are made using series and parallel strings of breakdown diodes, see clauses 9.1 and 9.2.
+
+Breakdown diodes do not have the same energy capability as metal-oxide varistor (MOV) protection components and are best placed where the transient is either already limited or has the highest source impedance, which is usually at the protected load. For example, to limit transient voltages, a breakdown diode could be connected across the primary winding or secondary winding of a mains transformer. The secondary winding is preferable as the transformer leakage inductance increases the source impedance of the transient on the secondary side and the protection is applied closest to the load; see Figure 27.
+
+![Figure 27: Placement of breakdown diode on a transformer circuit diagram. It shows a transformer with a primary winding connected to 'AC mains' and a secondary winding. A bidirectional breakdown diode is connected across the secondary winding. The diagram is labeled K.103(15)_F27.](6ca05954842b17f14dfd52f26b9d43d2_img.jpg)
+
+Figure 27: Placement of breakdown diode on a transformer circuit diagram. It shows a transformer with a primary winding connected to 'AC mains' and a secondary winding. A bidirectional breakdown diode is connected across the secondary winding. The diagram is labeled K.103(15)\_F27.
+
+**Figure 27 – Placement of breakdown diode on a transformer**
+
+## 9.5 Signal protection
+
+There are many types of information and communication technology (ICT) signals. The following clauses provide possible protection schemes for the signal types listed. Each example notes the protection and shows the outline circuit design.
+
+### 9.5.1 Power line communication (PLC) power line coupling
+
+Protection: Two bidirectional breakdown diodes and rectifiers
+
+![Circuit diagram for PLC power line coupling showing transmitter and receiver connected to AC mains via a transformer and protection components.](744acfe8d4e31bcf03f95714c2f6e567_img.jpg)
+
+The diagram illustrates a power line communication (PLC) coupling circuit. On the left, a 'TRANSMITTER' and a 'RECEIVER' are shown. The transmitter is connected to a network of two bidirectional breakdown diodes and a rectifier. The receiver is connected to a similar network. Both networks are coupled to an 'AC MAINS' line through a transformer. The transformer's primary winding is connected to the transmitter/receiver network, and its secondary winding is connected to the AC mains. The diagram is labeled 'K.103(15)\_F28'.
+
+Circuit diagram for PLC power line coupling showing transmitter and receiver connected to AC mains via a transformer and protection components.
+
+Figure 28 – Example of power line communication (PLC) power line coupling
+
+### 9.5.2 USB 2.0 port
+
+Protection: Double bridged punch-through diode
+
+![Circuit diagram for twin USB 2.0 port showing a USB controller connected to two USB ports with protection circuitry.](5b6e139e89c6ce90107ea7d7d77620a0_img.jpg)
+
+The diagram shows a 'USB CONTROLLER' connected to two 'USB PORT' blocks. Each USB port has pins for VDD, D+, D-, and GND. The controller is connected to the D+ and D- lines of both ports through resistors. Protection circuitry, consisting of double bridged punch-through diodes, is connected between the D+ and D- lines and the VDD and GND lines. The diagram is labeled 'K.103(15)\_F29'.
+
+Circuit diagram for twin USB 2.0 port showing a USB controller connected to two USB ports with protection circuitry.
+
+Figure 29 – Example of twin USB 2.0 port
+
+### 9.5.3 USB 3.0 port
+
+Protection: Triple bridged array with supply clamp and punch-through diode
+
+![Circuit diagram and I-V graph for a USB 3.0 port protection scheme.](ec36a1ba48e13289c395fab4a7730bdb_img.jpg)
+
+The figure illustrates the protection circuit for a USB 3.0 port. It consists of an I/O PORT connected to IC DATA LINES through a triple bridged array. The array includes supply clamps and punch-through diodes connected to VDD and GND. An inset graph shows the Current (A) versus Voltage (V) characteristics for the protection diodes. The red curve represents the VDD to GND clamping characteristic, and the black curve represents the I/O to GND clamping characteristic.
+
+| Voltage (V) | Current (A) VDD to GND (Red) | Current (A) I/O to GND (Black) |
+|-------------|------------------------------|--------------------------------|
+| 0           | 0                            | 0                              |
+| 5           | 0                            | 0                              |
+| 6           | 0                            | 0                              |
+| 7           | 10                           | 2                              |
+| 8           | 16                           | 6                              |
+| 9           | -                            | 10                             |
+| 10          | -                            | 12                             |
+| 11          | -                            | 14                             |
+| 12          | -                            | 16                             |
+| 13          | -                            | 18                             |
+
+K.103(15)\_F30
+
+Circuit diagram and I-V graph for a USB 3.0 port protection scheme.
+
+Figure 30 – Example of USB 3.0 port
+
+### 9.5.4 Ethernet PHY port
+
+Protection: Bridged protector on each physical layer (PHY) conductor
+
+![Circuit diagram of an Ethernet PHY port showing a Gigabit Ethernet Transceiver connected to a Magnetic, Terminations and Jack via four pairs of conductors (TP0PA, TP0NA, TP0PB, TP0NB, TP0PC, TP0NC, TP0PD, TP0ND). Each pair includes a bridged protector circuit.](14252bcd35912bd656e98b16b2ee51c0_img.jpg)
+
+The diagram illustrates the internal circuitry of an Ethernet PHY port. On the left, a block labeled "GIGABIT ETHERNET TRANSCEIVER" is connected to eight pins: TPOP0A, TP0NA, TPOP0B, TP0NB, TPOP0C, TP0NC, TPOP0D, and TP0ND. These pins are arranged in four pairs. Each pair (e.g., TPOP0A and TP0NA) is connected to a bridged protector circuit. Each protector consists of two bridge rectifiers. The first bridge is connected between the two conductors of the pair, with its output connected to ground through a resistor. The second bridge is connected between the conductors and the "MAGNETIC, TERMINATIONS AND JACK" block, with its output also connected to ground through a resistor. The "MAGNETIC, TERMINATIONS AND JACK" block is shown on the right side of the diagram. The reference "K.103(15)\_F31" is located in the bottom right corner.
+
+Circuit diagram of an Ethernet PHY port showing a Gigabit Ethernet Transceiver connected to a Magnetic, Terminations and Jack via four pairs of conductors (TP0PA, TP0NA, TP0PB, TP0NB, TP0PC, TP0NC, TP0PD, TP0ND). Each pair includes a bridged protector circuit.
+
+Figure 31 – Example of Ethernet PHY port
+
+### 9.5.5 IC data lines
+
+Protection: Quadruple bridged, punch-through diode array
+
+![Circuit diagram for IC data lines showing an LVDS INTERFACE connected to an LVDS CONTROLLER via multiple data lines (CLK+, CLK-, A0+, A0-, A1+, A1-, A2+, A2-). Each line is protected by a quadruple bridged, punch-through diode array connected to ground.](318886a86a1dcc59e1fc83db6f157c60_img.jpg)
+
+The diagram shows an LVDS INTERFACE on the left and an LVDS CONTROLLER on the right. Between them are eight data lines labeled CLK+, CLK-, A0+, A0-, A1+, A1-, A2+, and A2-. Each line has a protection circuit consisting of four diodes in a bridge configuration with a punch-through diode to ground. The protection circuits are connected to a common ground point. The reference code K.103(15)\_F32 is shown in the bottom right corner.
+
+Circuit diagram for IC data lines showing an LVDS INTERFACE connected to an LVDS CONTROLLER via multiple data lines (CLK+, CLK-, A0+, A0-, A1+, A1-, A2+, A2-). Each line is protected by a quadruple bridged, punch-through diode array connected to ground.
+
+Figure 32 – Example of IC data lines
+
+### 9.5.6 DS1 (T1/E1/J1) high-bit-rate digital subscriber line (HDSL) 4 ports
+
+Protection: Low capacitance and double bridged protectors
+
+![Circuit diagram for DS1 (T1/E1/J1) HDSL 4 ports showing a TI/E1 TRANSCEIVER connected to four ports (RRING, RTIP, TRING, TTIP). Each port is connected to a low capacitance and double bridged protector circuit, which is then connected to a transformer and a varistor.](dbbc0baac7341cda76cc4f8355dce23f_img.jpg)
+
+The diagram shows a TI/E1 TRANSCEIVER on the left with four ports: RRING, RTIP, TRING, and TTIP. Each port is connected to a protection circuit. The RTIP and TTIP lines first pass through a quadruple bridged, punch-through diode array connected to ground. All four lines then pass through a series of components: a resistor, a common-mode choke (transformer), and a varistor labeled with the Greek letter theta (θ). The reference code K.103(15)\_F33 is shown in the bottom right corner.
+
+Circuit diagram for DS1 (T1/E1/J1) HDSL 4 ports showing a TI/E1 TRANSCEIVER connected to four ports (RRING, RTIP, TRING, TTIP). Each port is connected to a low capacitance and double bridged protector circuit, which is then connected to a transformer and a varistor.
+
+Figure 33 – Example of DS1 (T1/E1/J1) HDSL 4 ports
+
+### 9.5.7 DS3 (T3/E3) ports
+
+Protection: Single and double bridged breakdown diodes
+
+![Circuit diagram of a DS3 (T3/E3) port showing internal components and external connections.](cfb98c691c1af5befe32ff9442eea511_img.jpg)
+
+The diagram illustrates the internal circuitry of a DS3, T3, E3, or STS-1 port. On the left, a large rectangular block represents the port interface. Two internal lines extend from this block, each passing through a resistor and then a transformer. After the transformers, each line connects to an external input labeled 'INPUT J1' and 'INPUT J2'. Each input line is followed by a double bridged breakdown diode assembly connected to ground, and then a capacitor connected to ground. A central bridge diode assembly is also shown, connected between the two internal lines and ground. The diagram is labeled 'K.103(15)\_F34' at the bottom right.
+
+Circuit diagram of a DS3 (T3/E3) port showing internal components and external connections.
+
+Figure 34 – Example of DS3 (T3/E3) ports
+
+### 9.5.8 Symmetrical digital subscriber line (SDSL) port
+
+Protection: Bridged and low-capacitance protection
+
+![Circuit diagram of an SDSL port showing internal components and external connections.](a1890b9a9b85f13e67ed59bbad623659_img.jpg)
+
+The diagram illustrates the internal circuitry of an SDSL port. On the left, a large rectangular block represents the port interface with pins labeled LDOUTN, LDOUTP, HYBP, HYBN, REVN, and REVP. A 5V supply is connected to the top pin. The HYBP and HYBN pins are connected to a bridge diode assembly with capacitors and resistors. The LDOUTN and LDOUTP pins are connected to external lines through resistors. These lines pass through a transformer and then to external components: a varistor (labeled with the Greek letter theta) and a diode assembly connected to ground. A central bridge diode assembly is connected between the internal lines and a VCC supply. The diagram is labeled 'K.103(15)\_F35' at the bottom right.
+
+Circuit diagram of an SDSL port showing internal components and external connections.
+
+Figure 35 – Example of SDSL port
+
+# Bibliography
+
+- [b-ITU-T K.96] Recommendation ITU-T K.96 (2014), *Surge protective components: Overview of surge mitigation functions and technologies.*
+- [b-IEC 60050-521] IEC 60050-521 (2002), *International Electrotechnical Vocabulary – Part 521: Semiconductor devices and integrated circuits.*
+- [b-IEC 60664-2-1] IEC 60664-2-1 (2011), *Insulation coordination for equipment within low-voltage systems – Part 2-1: Application guide – Explanation of the application of the IEC 60664 series, dimensioning examples and dielectric testing.*
+- [b-IEC 60747-2] IEC 60747-2 (2000), *Semiconductor devices – Discrete devices and integrated circuits – Part 2: Rectifier diodes.*
+- [b-IEC 61836] IEC TS 61836 (2007), *Solar photovoltaic energy systems – Terms, definitions and symbols.*
+- [b-Baliga] Baliga, B. Jayant (1987), *Modern Power Devices*, John Wiley & Sons, Inc.
+- [b-Clark] Clark, O. Melville, (1977), *Surge life of transient voltage suppressors, final report*, General Semiconductor Industries, Inc.  
+<<http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19780007453.pdf>>
+- [b-King] Ya-Chin King, Bin Yu, Jeff Pohlman and Chenming Hu (1996), *Punchthrough diode as the transient voltage suppressor for low-voltage electronics*, IEEE Transactions on Electron devices, Vol. 43, No. 11, November.
+- [b-Lindmayer] Lindmayer, J and Wrigley, C.Y. (1966), *Fundamentals of Semiconductor Devices*, Van Nostrand Company, New York.
+- [b-McKay] McKay, K.G. and McAfee, K.B. (1953), *Electron Multiplication in Silicon and Germanium*, Physics Review, Vol. 91, p. 1079.
+- [b-Zener] C. Zener, (1934), *A Theory of the Electrical Breakdown of Solid Dielectrics*, Proceedings A, Royal Society Publishing (London), Vol. 145, No. 855, p. 523.
+
+
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                             |
+|-----------------|---------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                           |
+| Series D        | General tariff principles                                                                   |
+| Series E        | Overall network operation, telephone service, service operation and human factors           |
+| Series F        | Non-telephone telecommunication services                                                    |
+| Series G        | Transmission systems and media, digital systems and networks                                |
+| Series H        | Audiovisual and multimedia systems                                                          |
+| Series I        | Integrated services digital network                                                         |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals |
+| <b>Series K</b> | <b>Protection against interference</b>                                                      |
+| Series L        | Construction, installation and protection of cables and other elements of outside plant     |
+| Series M        | Telecommunication management, including TMN and network maintenance                         |
+| Series N        | Maintenance: international sound programme and television transmission circuits             |
+| Series O        | Specifications of measuring equipment                                                       |
+| Series P        | Terminals and subjective and objective assessment methods                                   |
+| Series Q        | Switching and signalling                                                                    |
+| Series R        | Telegraph transmission                                                                      |
+| Series S        | Telegraph services terminal equipment                                                       |
+| Series T        | Terminals for telematic services                                                            |
+| Series U        | Telegraph switching                                                                         |
+| Series V        | Data communication over the telephone network                                               |
+| Series X        | Data networks, open system communications and security                                      |
+| Series Y        | Global information infrastructure, Internet protocol aspects and next-generation networks   |
+| Series Z        | Languages and general software aspects for telecommunication systems                        |

marked/K/T-REC-K.105-201503-I_PDF-E/raw.md

@@ -0,0 +1,363 @@
+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**K.105**
+
+(03/2015)
+
+SERIES K: PROTECTION AGAINST INTERFERENCE
+
+---
+
+**Lightning protection of photovoltaic power  
+supply systems feeding radio base stations**
+
+Recommendation ITU-T K.105
+
+![ITU logo](6ed175c791b5e156d9c98a8dbcc3318c_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a globe with a red lightning bolt striking it, symbolizing telecommunications and protection against interference. To the right of the globe, the text "International Telecommunication Union" is written in a blue, sans-serif font.
+
+ITU logo
+
+International  
+Telecommunication  
+Union
+
+
+
+# Recommendation ITU-T K.105
+
+## Lightning protection of photovoltaic power supply systems feeding radio base stations
+
+## Summary
+
+Recommendation ITU-T K.105 provides lightning protection procedures for protecting dedicated photovoltaic (PV) power supply systems used to provide electric power to radio base stations (RBSs). This Recommendation describes the bonding and earthing procedures applied to the metallic supports of the PV array, considering the following scenarios for the installation of the PV array: ground surfaces, rooftops and towers. For each scenario, the possibility of installing the electronic controller close to the PV array or close to the DC load is considered. This Recommendation also provides the configuration and rating of protection modules required to protect the electronic controller and the PV array against lightning surges.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T K.105    | 2015-03-01 | 5           | <a href="http://handle.itu.int/11.1002/1000/12425">11.1002/1000/12425</a> |
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2015
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                                               | Page |
+|-------------------------------------------------------------------------------|------|
+| 1 Scope.....                                                                  | 1    |
+| 2 References.....                                                             | 1    |
+| 3 Definitions .....                                                           | 1    |
+| 3.1 Terms defined elsewhere .....                                             | 1    |
+| 3.2 Terms defined in this Recommendation.....                                 | 1    |
+| 4 Abbreviations and acronyms .....                                            | 2    |
+| 5 Conventions .....                                                           | 2    |
+| 6 The photovoltaic power supply system .....                                  | 2    |
+| 7 Direct lightning protection of PV power supply systems.....                 | 2    |
+| 8 Earthing and bonding of PV power supply systems.....                        | 2    |
+| 8.1 Earthing and bonding of the PV module support .....                       | 2    |
+| 8.2 Earthing and bonding of the PV power supply .....                         | 4    |
+| 9 Current capability of the protective module in PV power supply systems..... | 7    |
+
+
+
+# Recommendation ITU-T K.105
+
+## Lightning protection of photovoltaic power supply systems feeding radio base stations
+
+# 1 Scope
+
+This Recommendation addresses the lightning protection of photovoltaic (PV) power supply systems that are used exclusively for feeding radio base stations (RBSs). The purpose of this Recommendation is to give guidance on the earthing, bonding and protection of PV power supply systems.
+
+# 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T K.56] Recommendation ITU-T K.56 (2010), *Protection of radio base stations against lightning discharges*.
+- [ITU-T K.71] Recommendation ITU-T K.71 (2007), *Protection of customer antenna installations*.
+- [ITU-T K.97] Recommendation ITU-T K.97 (2014), *Lightning protection of distributed base stations*.
+- [IEC 61643-11] IEC 61643-11 (2011), *Low-voltage surge protective devices – Part 11: Surge protective devices connected to low-voltage power systems – Requirements and test methods*.
+- [IEC 62305-1] IEC 62305-1 (2010), *Protection against lightning – Part 1: General principles*.
+- [IEC 62305-2] IEC 62305-2 (2010), *Protection against lightning – Part 2: Risk management*.
+- [IEC 62305-3] IEC 62305-3 (2010), *Protection against lightning – Part 3: Physical damage to structures and life hazard*.
+- [IEC 62305-4] IEC 62305-4 (2010), *Protection against lightning – Part 4: Electric and electronic systems within structures*.
+
+# 3 Definitions
+
+## 3.1 Terms defined elsewhere
+
+None.
+
+## 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following term:
+
+**3.2.1 earthing network:** The part of an earthing installation that is restricted to the earth electrodes and their interconnections.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+PV Photovoltaic
+
+RBS Radio Base Station
+
+# 5 Conventions
+
+None.
+
+# 6 The photovoltaic power supply system
+
+The photovoltaic (PV) power supply system generates electricity based on the photoelectric effect. It consists of the PV module, PV module support, junction box, PV controller and battery. The PV power supply system considered in this Recommendation is exclusive for feeding the radio base station (RBS) and does not feed the public electric network. Figure 1 shows the diagram of a typical PV power supply system.
+
+![Figure 1 – Photovoltaic power supply system network diagram. The diagram shows a PV module connected to a junction box, which is connected to a PV controller. The PV controller is connected to a DC load. A battery is connected to the PV controller via a signal cable. A legend indicates that solid blue arrows represent DC cables and dashed black arrows represent signal cables. The diagram is labeled K.105(15)_F01.](e1a0d046fbe7f28f5e93a47091851747_img.jpg)
+
+```
+graph LR; PV[PV module] -- DC cable --> JB[Junction box]; JB -- DC cable --> PC[PV controller]; PC -- DC cable --> DL[DC load]; PC <--> |Signal cable| B[Battery];
+```
+
+Figure 1 – Photovoltaic power supply system network diagram. The diagram shows a PV module connected to a junction box, which is connected to a PV controller. The PV controller is connected to a DC load. A battery is connected to the PV controller via a signal cable. A legend indicates that solid blue arrows represent DC cables and dashed black arrows represent signal cables. The diagram is labeled K.105(15)\_F01.
+
+Figure 1 – Photovoltaic power supply system network diagram
+
+# 7 Direct lightning protection of PV power supply systems
+
+Each part of the PV power supply system should be installed within the protection zone of an RBS air termination system. The design and installation of an air termination system to protect the PV power supply system is outside the scope of this Recommendation. Users are advised to consult the appropriate documents on this topic.
+
+The PV power supply system should share the same earthing network with the radio base station.
+
+# 8 Earthing and bonding of PV power supply systems
+
+## 8.1 Earthing and bonding of the PV module support
+
+The PV module support is normally formed by its metallic structure, as illustrated in Figure 2.
+
+If the metallic structure is constructed of many separated supports, the adjacent supports shall be bonded together by a bonding conductor, as shown in Figure 2. The cross-sectional area of the bonding conductor shall not be less than  $6 \text{ mm}^2$ .
+
+The PV module support should be bonded to the earthing network, at least at two points, as shown in Figure 2. The cross-sectional area of the bonding conductor shall not be less than  $16 \text{ mm}^2$ .
+
+![Figure 2: Bonding connections of separate supports. This 3D diagram shows a series of individual metal supports, each with its own concrete foundation. Red lines represent bonding conductors connecting adjacent supports to each other and to a common earthing network. Labels include 'Bonding between supports', 'Separate support', 'Foundation of support', 'Earthing network of the site', and 'Support bonded to earthing network'.](fd955384881fd240be5518d3050588d9_img.jpg)
+
+Figure 2: Bonding connections of separate supports. This 3D diagram shows a series of individual metal supports, each with its own concrete foundation. Red lines represent bonding conductors connecting adjacent supports to each other and to a common earthing network. Labels include 'Bonding between supports', 'Separate support', 'Foundation of support', 'Earthing network of the site', and 'Support bonded to earthing network'.
+
+**Figure 2 – Bonding connections of separate supports**
+
+When the module supports are integrated into a single metallic structure that ensures the electrical continuity between the individual supports, no additional bonding conductor is required between two adjacent supports. The metallic supports shall be bonded to the earthing network, at least at two points, as shown in Figure 3. The cross-sectional area of the bonding conductor shall not be less than 16 mm<sup>2</sup>.
+
+![Figure 3: Earthing and bonding of a united support. This 3D diagram shows a single, continuous metal structure (a 'united support') with multiple legs. Red lines show the connection points to a 'ring conductor of earthing network'. Labels include 'United support', 'Bonded to earthing network at least at two points', and 'Ring conductor of earthing network'.](c37fe03d7cad74ad675a0eb16aa43821_img.jpg)
+
+Figure 3: Earthing and bonding of a united support. This 3D diagram shows a single, continuous metal structure (a 'united support') with multiple legs. Red lines show the connection points to a 'ring conductor of earthing network'. Labels include 'United support', 'Bonded to earthing network at least at two points', and 'Ring conductor of earthing network'.
+
+**Figure 3 – Earthing and bonding of a united support**
+
+## 8.2 Earthing and bonding of the PV power supply
+
+The junction box that is installed on the PV module support should not be insulated from the support. The bonding conductor of the junction box shall be directly bonded to the PV module support.
+
+The cross-sectional area of the bonding conductors on the PV controller and junction box shall not be less than 6 mm<sup>2</sup>.
+
+PV power supply systems are applied in the following three scenarios: PV supports installed on the ground, PV supports installed on a rooftop, and PV supports installed on a tower.
+
+### 8.2.1 Scenario A: PV support installed on the ground
+
+![Diagram illustrating earthing and bonding for Scenario A: PV support installed on the ground. The diagram shows a PV array mounted on a reinforced concrete base, which is bonded to the RBS earthing network at two points. The PV array is connected to a Diesel generator and an Equipment room. A Tower is also shown, connected to the earthing network.](b8661c6c54f72ecc7ff6cb05e47b2891_img.jpg)
+
+The diagram shows a site layout with the following components and connections:
+
+- PV array:** A series of solar panels mounted on a support structure. The support structure is anchored into a **Reinforced concrete base**.
+- Reinforced concrete base:** Shown as a yellow-shaded area. It is bonded to the **RBS earthing network** at two points, indicated by black dots and lines.
+- Diesel generator:** Represented by a small blue rectangle.
+- Equipment room:** A large rectangular building with a blue outline.
+- Tower:** A tall structure with a blue outline, connected to the earthing network at its base and top.
+- Earthing network:** A network of conductors (blue lines) connecting the PV array support, the Diesel generator, the Equipment room, and the Tower to a common earthing point.
+
+Reference code: K.105(15)\_F04
+
+Diagram illustrating earthing and bonding for Scenario A: PV support installed on the ground. The diagram shows a PV array mounted on a reinforced concrete base, which is bonded to the RBS earthing network at two points. The PV array is connected to a Diesel generator and an Equipment room. A Tower is also shown, connected to the earthing network.
+
+**Figure 4 – Earthing and bonding when the PV support is installed on the ground**
+
+In this scenario, the reinforced concrete base of the PV support should be bonded to the RBS earthing network at least at two points, as illustrated in Figure 4.
+
+Depending on the installation of the PV controller and the junction box, this scenario can be classified into the scenarios A-1 and A-2, as shown in Figures 5 and 6, respectively.
+
+#### 8.2.1.1 Scenario A-1: PV controller installed close to the junction box
+
+![Diagram of earthing and bonding for Scenario A-1: PV controller installed close to the junction box.](5b4e774d63e0e0ed73801a9247755e5f_img.jpg)
+
+This diagram illustrates the earthing and bonding configuration for Scenario A-1. A PV array is mounted on a metal support structure. A junction box is connected to the PV array. A PV controller is installed close to the junction box. The DC output port of the PV controller is connected to the junction box. The junction box and the PV controller are bonded to the metallic support structure. The metallic support structure is bonded to the earthing network. The earthing network is shown as a horizontal line at the bottom of the diagram. The text 'PV controller installed close to junction box' and the code 'K.105(15)\_F05' are present at the bottom of the diagram.
+
+Diagram of earthing and bonding for Scenario A-1: PV controller installed close to the junction box.
+
+**Figure 5 – Earthing and bonding when the PV controller is installed close to the junction box**
+
+In this case, the PV controller is usually installed outdoors.
+
+The bonding conductors of the junction box and the PV controller shall be bonded to the metallic support directly and these conductors shall be as short as possible.
+
+The DC power output cable of the PV controller shall be buried in the earth or put in a metallic cable tray above the earth's surface. The cable tray shall be electrical continuous and bonded to the earthing network at both ends.
+
+#### 8.2.1.2 Scenario A-2: PV controller installed close to the DC load
+
+![Diagram of earthing and bonding for Scenario A-2: PV controller installed near DC load.](8e14350b4b669119a3bdfca7869110ca_img.jpg)
+
+This diagram illustrates the earthing and bonding configuration for Scenario A-2. A PV array is mounted on a metal support structure. A junction box is connected to the PV array. The PV controller is installed in an equipment room, close to a DC load (BTS). The DC output port of the PV controller is connected to the junction box. The junction box and the PV controller are bonded to the metallic support structure. The metallic support structure is bonded to the earthing network. The earthing network is shown as a horizontal line at the bottom of the diagram. The text 'PV controller installed near DC load' and the code 'K.105(15)\_F06' are present at the bottom of the diagram. A main earthing bar is also shown in the equipment room, connected to the BTS and the PV controller.
+
+Diagram of earthing and bonding for Scenario A-2: PV controller installed near DC load.
+
+**Figure 6 – Earthing and bonding when the PV controller is installed close to the DC load**
+
+In this case, the PV controller is usually installed in a traditional equipment room, in an outdoor cabinet or in a mini-shelter.
+
+The bonding conductor of the PV controller shall be bonded to the earthing bar of the equipment room, outdoor cabinet or mini-shelter.
+
+The DC power input cable of the PV controller shall be buried in the earth or put in a metal cable tray above the earth's surface. The cable tray shall be electrical continuous and bonded to the earthing network at both ends.
+
+### 8.2.2 Scenario B: PV Module support installed on a rooftop
+
+![Diagram illustrating earthing and bonding for PV modules installed on a rooftop. The diagram shows a rooftop with an 'Equipment room' (a rectangular structure) and a tall 'PV Module support' (a vertical lattice structure). A 'Junction box' is located on the roof near the equipment room. A 'Ring earthing network' is shown as a dashed red line around the base of the equipment room. Solid blue lines represent bonding conductors connecting the junction box and the PV support to the ring earthing network. The diagram is labeled 'K.105(15)_F07' in the bottom right corner.](4d2624b1b2871a23382b647cd71e1c1c_img.jpg)
+
+Diagram illustrating earthing and bonding for PV modules installed on a rooftop. The diagram shows a rooftop with an 'Equipment room' (a rectangular structure) and a tall 'PV Module support' (a vertical lattice structure). A 'Junction box' is located on the roof near the equipment room. A 'Ring earthing network' is shown as a dashed red line around the base of the equipment room. Solid blue lines represent bonding conductors connecting the junction box and the PV support to the ring earthing network. The diagram is labeled 'K.105(15)\_F07' in the bottom right corner.
+
+**Figure 7 – Earthing and bonding when the PV support is installed on the rooftop**
+
+In this case, the metallic PV support should be bonded to the earthing network by at least two down conductors.
+
+Based on the installation of the PV controller and the junction box, this scenario can be classified into the following two sub-scenarios:
+
+#### 8.2.2.1 Scenario B-1: The PV controller is installed close to the junction box
+
+In this case, the PV controller is usually installed outdoor.
+
+The bonding conductors of the junction box and the PV controller should be bonded to the metallic support directly and these conductors shall be as short as possible.
+
+#### 8.2.2.2 Scenario B-2: The PV controller is installed close to the DC load
+
+In this case, the PV controller is usually installed in the equipment room, outdoor cabinet or mini-shelter.
+
+The bonding conductor of the PV controller shall be bonded to the earthing bar of equipment room, cabinet or mini-shelter.
+
+The DC power input cable of the PV controller shall be installed in a metallic cable tray. The cable tray shall be electrical continuous and bonded to the RBS earthing network at both ends.
+
+### 8.2.3 Scenario C: PV support installed on a tower
+
+![Figure 8: Earthing and bonding when PV support is installed on the tower. The image shows two scenarios: on the left, a PV panel mounted on a stand connected to an earthing network; on the right, a PV panel mounted on a lattice tower structure.](0cc86fe8fc37b0edc9581f2af9459a52_img.jpg)
+
+Figure 8: Earthing and bonding when PV support is installed on the tower. The image shows two scenarios: on the left, a PV panel mounted on a stand connected to an earthing network; on the right, a PV panel mounted on a lattice tower structure.
+
+**Figure 8 – Earthing and bonding when PV support is installed on the tower**
+
+In this scenario, the following requirements should be met:
+
+The PV support shall be bonded to the metallic tower by using appropriate metallic accessories. No dedicated bonding conductor is required. The tower shall be free of paint before the installation of the PV support and anti-corrosion measures should be taken after the PV support is properly installed.
+
+The junction box shall be installed on the PV support, and the bonding conductor of the junction box shall be connected to the metallic PV support directly.
+
+The bonding bar of the PV controller shall be connected to the PV support when the PV controller is installed outdoors, or connected to the main earthing bar of the cabinet when the PV controller is installed in an outdoor cabinet.
+
+# 9 Current capability of the protective module in PV power supply systems
+
+The PV controller needs to be protected against lightning by a protective module at the PV input port, at the load output port and at the controller signal port. Protective modules can be integrated into the PV controller or installed close to the PV controller. The bonding configurations are shown in Figures 9 and 10.
+
+![Figure 9: Bonding of the protective modules when they are installed inside the PV controller. The diagram shows a PV controller box with three input ports: PV input, Controller signal port, and Load output. Each port has a protective module (represented by a square symbol) connected to it. The protective modules are bonded to the PV controller box. The Load output is shown as an output from the PV controller box.](5a9282ac54ca7bc50f1d2ab6cfb376ba_img.jpg)
+
+K.105(15)\_F09
+
+Figure 9: Bonding of the protective modules when they are installed inside the PV controller. The diagram shows a PV controller box with three input ports: PV input, Controller signal port, and Load output. Each port has a protective module (represented by a square symbol) connected to it. The protective modules are bonded to the PV controller box. The Load output is shown as an output from the PV controller box.
+
+**Figure 9 – Bonding of the protective modules when they are installed inside the PV controller**
+
+![Figure 10: Bonding of the protective modules when they are installed outside the PV controller. The diagram shows a central 'PV controller' box with three ports: 'PV input' (top left), 'Load output' (top right), and 'Controller signal port' (bottom center). Two 'Protection modules' are shown on the left, connected to the 'PV input' and 'Controller signal port' respectively. Two more 'Protection modules' are shown on the right, connected to the 'Load output'. All four protection modules are connected to a common 'Bonding bar for PV controller' at the bottom. The diagram is labeled K.105(15)_F10.](4801720824e4b5e2361a5564f91cfb70_img.jpg)
+
+Figure 10: Bonding of the protective modules when they are installed outside the PV controller. The diagram shows a central 'PV controller' box with three ports: 'PV input' (top left), 'Load output' (top right), and 'Controller signal port' (bottom center). Two 'Protection modules' are shown on the left, connected to the 'PV input' and 'Controller signal port' respectively. Two more 'Protection modules' are shown on the right, connected to the 'Load output'. All four protection modules are connected to a common 'Bonding bar for PV controller' at the bottom. The diagram is labeled K.105(15)\_F10.
+
+**Figure 10 – Bonding of the protective modules when they are installed outside the PV controller**
+
+As the configuration shown in Figure 9 requires shorter bonding conductors for the protective modules than the one shown in Figure 10, it provides a more effective protection. Thus, if possible, the configuration shown in Figure 9 should be preferable.
+
+The recommended surge current capability of the protective module of the PV controller is listed in the Table 1. The protection module at each port should withstand the surge current for five times each polarity, as indicated in Table 1.
+
+**Table 1 – Minimum current capability of the protective module of the PV controller**
+
+| Port                   | Specification | Waveshape    | Repetition | Comments                                                        |
+|------------------------|---------------|--------------|------------|-----------------------------------------------------------------|
+| PV input               | 5 kA          | 8/20 $\mu$ s | $\pm 5$    |                                                                 |
+| Load output            | 5 kA          | 8/20 $\mu$ s | $\pm 5$    | PV controller does not power equipment on the top of the tower  |
+|                        | 20 kA         | 8/20 $\mu$ s | $\pm 5$    | PV controller powers equipment on the top of the tower directly |
+| Controller signal port | 3 kA          | 8/20 $\mu$ s | $\pm 5$    |                                                                 |
+
+In some cases, the PV array and the junction box need to be protected by a protective module at the junction box output port. For example, if the diode circuits in the PV array are not insulated from the metallic shell of PV array. In this case, it is recommended to install a protective module into junction box.
+
+The recommended surge current capability of protective module of the junction box is listed in Table 2.
+
+**Table 2 – Minimum current capability of the protective module of the junction box**
+
+| Port      | Specification | Waveshape    | Repetition | Comments |
+|-----------|---------------|--------------|------------|----------|
+| DC output | 5 kA          | 8/20 $\mu$ s | $\pm 5$    | Optional |
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                             |
+|-----------------|---------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                           |
+| Series D        | General tariff principles                                                                   |
+| Series E        | Overall network operation, telephone service, service operation and human factors           |
+| Series F        | Non-telephone telecommunication services                                                    |
+| Series G        | Transmission systems and media, digital systems and networks                                |
+| Series H        | Audiovisual and multimedia systems                                                          |
+| Series I        | Integrated services digital network                                                         |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals |
+| <b>Series K</b> | <b>Protection against interference</b>                                                      |
+| Series L        | Construction, installation and protection of cables and other elements of outside plant     |
+| Series M        | Telecommunication management, including TMN and network maintenance                         |
+| Series N        | Maintenance: international sound programme and television transmission circuits             |
+| Series O        | Specifications of measuring equipment                                                       |
+| Series P        | Terminals and subjective and objective assessment methods                                   |
+| Series Q        | Switching and signalling                                                                    |
+| Series R        | Telegraph transmission                                                                      |
+| Series S        | Telegraph services terminal equipment                                                       |
+| Series T        | Terminals for telematic services                                                            |
+| Series U        | Telegraph switching                                                                         |
+| Series V        | Data communication over the telephone network                                               |
+| Series X        | Data networks, open system communications and security                                      |
+| Series Y        | Global information infrastructure, Internet protocol aspects and next-generation networks   |
+| Series Z        | Languages and general software aspects for telecommunication systems                        |

marked/K/T-REC-K.106-201503-I_PDF-E/raw.md

@@ -0,0 +1,887 @@
+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**K.106**
+
+(03/2015)
+
+# **SERIES K: PROTECTION AGAINST INTERFERENCE** ---
+
+**Techniques to mitigate interference between  
+radio devices and cable or equipment  
+connected to wired broadband networks and  
+cable television networks**
+
+Recommendation ITU-T K.106
+
+**ITU-T**
+
+![ITU logo](84a1d09fb489061482111515543b60dc_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a globe with a red lightning bolt striking across it. To the right of the globe, the text "International Telecommunication Union" is written in blue, with "ITU" in a larger, bold font above it.
+
+ITU logo
+
+International  
+Telecommunication  
+Union
+
+
+
+## Recommendation ITU-T K.106
+
+## Techniques to mitigate interference between radio devices and cable or equipment connected to wired broadband networks and cable television networks
+
+## Summary
+
+Recommendation ITU-T K.106 describes techniques used to mitigate the effects of interference between radio devices used in the home and cable or equipment connected to wired broadband networks and cable television networks. With the advancement of household appliances, many widely used devices are now connected to home networks. This Recommendation introduces the relevant electromagnetic compatibility (EMC) requirements applicable to wired home network devices, and feasible solutions to resolve EMC problems caused by the use of radio devices in proximity to other wired network equipment.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T K.106    | 2015-03-01 | 5           | <a href="http://handle.itu.int/11.1002/1000/12426">11.1002/1000/12426</a> |
+
+## Keywords
+
+Cables, home network, interference, wireless.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2015
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|              |                                                                                                                         | Page |
+|--------------|-------------------------------------------------------------------------------------------------------------------------|------|
+| 1            | Scope.....                                                                                                              | 1    |
+| 2            | References.....                                                                                                         | 1    |
+| 3            | Definitions .....                                                                                                       | 2    |
+| 3.1          | Terms defined elsewhere .....                                                                                           | 2    |
+| 3.2          | Terms defined in this Recommendation.....                                                                               | 2    |
+| 4            | Abbreviations and acronyms .....                                                                                        | 2    |
+| 5            | Conventions .....                                                                                                       | 3    |
+| 6            | Issues to be considered in this Recommendation .....                                                                    | 3    |
+| 6.1          | Background and problems .....                                                                                           | 3    |
+| 7            | Relevant requirements .....                                                                                             | 4    |
+| 7.1          | Relevant EMC standards for devices .....                                                                                | 4    |
+| 7.2          | Regional regulations .....                                                                                              | 4    |
+| 8            | Guidance to identify and address interference.....                                                                      | 4    |
+| 8.1          | Procedure to identify interference sources .....                                                                        | 4    |
+| 8.2          | Mitigation techniques applied to equipment connected to wired<br>broadband networks and cable television networks ..... | 7    |
+| 9            | Procedure for selecting appropriate mitigation techniques .....                                                         | 8    |
+| 9.1          | Checking information obtained from the measurement or interference<br>phenomena.....                                    | 8    |
+| 9.2          | Checking radio devices in normal operation and installation .....                                                       | 8    |
+| 9.3          | Adding appropriate mitigation measures.....                                                                             | 8    |
+| Appendix I   | – Examples of interference cases in the field.....                                                                      | 10   |
+| I.1          | Example 1: Interference between a mobile phone and a set top box .....                                                  | 10   |
+| I.2          | Example 2: Emission from connection at coaxial outlet and plug .....                                                    | 10   |
+| I.3          | Example 3: Emission from indoor cabling of CS/BS down-converted<br>signal.....                                          | 11   |
+| Appendix II  | – Examples of regional regulations for cable television networks.....                                                   | 13   |
+| II.1         | Overview .....                                                                                                          | 13   |
+| II.2         | Examples of regional regulations .....                                                                                  | 13   |
+| Appendix III | – Examples of measured emissions from coaxial cables and connectors .....                                               | 18   |
+| III.1        | Introduction .....                                                                                                      | 18   |
+| III.2        | Measurement set-up.....                                                                                                 | 18   |
+| III.3        | Measurement result .....                                                                                                | 18   |
+| Appendix IV  | – Information of radio communication systems related to safety issues .....                                             | 22   |
+| IV.1         | Radio communication related to aeronautical systems .....                                                               | 22   |
+| Bibliography | .....                                                                                                                   | 23   |
+
+## **Introduction**
+
+Along with advances in radio communication technologies, possible interference between home-use radio devices and telecommunication devices, such as cable or equipment connected to wired broadband networks and cable television networks are new phenomena. Interference to cabling or devices falls under the responsibility of ITU-T, whereas the interference between two (or more) radio devices falls under the responsibility of ITU-R. Such problems may occur in the field, especially in a home environment. This Recommendation provides guidance on how to solve problems arising from these kinds of phenomena by taking measures to reduce the interference and to ensure normal operating conditions of wired telecommunication equipment. Guidance on mitigation measures against radio devices is not provided in this Recommendation.
+
+## Recommendation ITU-T K.106
+
+## Techniques to mitigate interference between radio devices and cable or equipment connected to wired broadband networks and cable television networks
+
+# 1 Scope
+
+This Recommendation provides guidance to solve interference problems in home networking environments between radio devices and the cable or equipment connected to wired broadband networks and/or cable television networks. It also presents appropriate measures to be applied to the cable and the equipment connected to wired broadband networks and/or cable television networks for solving the interference and procedures to address these troubles in the field.
+
+The scope of this Recommendation focuses on procedures to identify the cause of interference problems in the home, and mitigation measures for the equipment or cabling needed to solve these problems. Mitigation techniques for the radio devices and interference problems between multiple radio devices are outside the scope of this Recommendation.
+
+Necessary electromagnetic compatibility (EMC) requirements for the equipment are given by relevant international standards, such as: [ITU-T K.74], [ITU-T K.93], [ITU-T K.37], [ITU-T K.43], [ITU-T K.48] and [IEC CISPR 22]. Moreover, interference related to power line communication (PLC) is outside the scope of this Recommendation, which is already covered by [ITU-T K.60].
+
+## 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T J.142] Recommendation ITU-T J.142 (2000), *Methods for the measurement of parameters in the transmission of digital cable television signals*.
+- [ITU-T K.34] Recommendation ITU-T K.34 (2003), *Classification of electromagnetic environmental conditions for telecommunication equipment – Basic EMC Recommendation*.
+- [ITU-T K.37] Recommendation ITU-T K.37 (1999), *Low and high frequency EMC mitigation techniques for telecommunication installations and systems – Basic EMC Recommendation*.
+- [ITU-T K.43] Recommendation ITU-T K.43 (2009), *Immunity requirements for telecommunication network equipment*.
+- [ITU-T K.48] Recommendation ITU-T K.48 (2006), *EMC requirements for telecommunication equipment – Product family Recommendation*.
+- [ITU-T K.60] Recommendation ITU-T K.60 (2008), *Emission levels and test methods for wireline telecommunication networks to minimize electromagnetic disturbance of radio services*.
+- [ITU-T K.74] Recommendation ITU-T K.74 (2008), *EMC, resistibility and safety requirements for home network devices*.
+
+- [ITU-T K.92] Recommendation ITU-T K.92 (2012), *Conducted and radiated electromagnetic environment in home networking*.
+- [ITU-T K.93] Recommendation ITU-T K.93 (2012), *Immunity of home network devices to electromagnetic disturbances*.
+- [ITU-T MTIM] ITU-T Handbook (2008), *Mitigation measures for telecommunication installation – Part 1*. ITU-T, Geneva.
+- [IEC 61000-2-5] IEC TR 61000-2-5 (2011), *Electromagnetic compatibility (EMC) – Part –2-5: Environment – Description and classification of electromagnetic environments*.
+- [IEC 60728-2] IEC 60728-2 (2010), *Cable networks for television signals, sound signals and interactive services – Part 2: Electromagnetic compatibility for equipment*.
+- [IEC 60728-12] IEC 60728-12 (2001), *Cabled distribution systems for television and sound signals – Part 12: Electromagnetic compatibility of systems*.
+- [IEC CISPR 22] IEC CISPR 22 (2008), *Information technology equipment – Radio disturbance characteristics – Limits and methods of measurement*.
+- [IEC CISPR 24] IEC CISPR 24 (2010), *Information technology equipment – Immunity characteristics – Limits and methods of measurement*.
+- [IEC CISPR 32] IEC CISPR 32 (2015), *Electromagnetic compatibility of multimedia equipment –Emission requirements*.
+
+# 3 Definitions
+
+### 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 cable television** [ITU-T J.142]: Communication systems that distribute broadcast and non-broadcast signals, as well as a multiplicity of satellite signals originating programming and other signals by means of coaxial cable and/or optical fibre.
+
+**3.1.2 home network device** [ITU-T K.74]: A home network device is an electronic/electric equipment whose primary function is the distribution of data within the home, between the network termination point and one or more terminal devices.
+
+**3.1.3 shielding effectiveness** [ITU-T K.43]: For a given external source, the ratio of electric or magnetic field strength at a point before and after the placement of the shield in question.
+
+### 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following term:
+
+**3.2.1 radio device**: A device, whose primary function is the transmission or reception of data by using radio waves in order to communicate with other devices; it does not require any physical wires for transmitting data to, or receiving data from, other devices.
+
+## 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|      |                                    |
+|------|------------------------------------|
+| AC   | Alternating Current                |
+| ADSL | Asymmetric Digital Subscriber Line |
+| BS   | Broadcasting satellite             |
+| CMC  | Common-Mode Choke                  |
+
+|      |                                        |
+|------|----------------------------------------|
+| CS   | Communication satellite                |
+| DC   | Direct Current                         |
+| DSL  | Digital Subscriber Line                |
+| DVB  | Digital Video Broadcasting             |
+| EM   | Electromagnetic                        |
+| EMC  | Electromagnetic Compatibility          |
+| EMI  | Electromagnetic Interference           |
+| HD   | High Definition                        |
+| IF   | Intermediate Frequency                 |
+| IMT  | International Mobile Telecommunication |
+| NGN  | Next Generation Network                |
+| PC   | Personal Computer                      |
+| PE   | Protective Earth                       |
+| PLC  | Power Line Communication               |
+| PSTN | Public Switched Telephone Network      |
+| RF   | Radio Frequency                        |
+| RFI  | Radio Frequency Interface              |
+| STB  | Set Top Box                            |
+| VoIP | Voice over Internet Protocol           |
+
+## 5 Conventions
+
+None.
+
+# 6 Issues to be considered in this Recommendation
+
+## 6.1 Background and problems
+
+With the widespread use of home networks, radio devices, including both new and conventional systems, could be used in close proximity to network cable or devices in the home. Thus, there is a possibility that new EMC problems may occur in the field. One concern is possible interference between radio devices, such as international mobile telecommunication (IMT) user equipment and cable or equipment connected to wired broadband networks and cable television networks. This may occur due to the lack of appropriate installation, such as faulty connections, damaged cables, overly close proximity of devices, etc. Therefore, part of this issue falls under EMC problems and requires necessary mitigation techniques. Key issues are to provide methodologies for preventing possible interference between devices and for providing appropriate measures to be applied to the equipment or cable connected to wired broadband and cable television networks.
+
+For example, if the connection between a coaxial cable and its connecter does not have sufficient electrical contact, then it may cause interference to wired broadcasting systems, radio devices or vice versa. Examples of these phenomena in the field are given in Appendices I and III. Therefore, an urgent issue is to take into consideration problems caused by wired broadband networks and cable television network installations.
+
+The area covered in this Recommendation is given in Figure 6-1. Interference into radio devices falls under the responsibility in ITU-R.
+
+![Diagram illustrating the area covered in this Recommendation for interference. A central yellow device (likely a base station or router) is shown with various connections and labels. A red dashed circle indicates the area of concern. Labels include: 'Immunity level of device', 'Emission from device', 'Broadband NW', 'Insufficient installation', 'Failure of connection', 'TEL', 'Emission from cable and induction to cable' (twice), and 'K.106(15)_F6-1'.](f4fdd410cdb84df81274da55721e56fb_img.jpg)
+
+The diagram shows a central yellow rectangular device with four green LEDs on its front panel. A red dashed circle is centered on this device, representing the area of concern. Various components are connected to or near the device: a 'TEL' (telephone) handset is connected to the top; a 'Broadband NW' (network) cable is connected to the left; a laptop and a monitor are connected to the right. Labels with leader lines point to specific parts of the diagram: 'Immunity level of device' points to the central device; 'Emission from device' points to the central device; 'Broadband NW' points to the network cable; 'Insufficient installation' and 'Failure of connection' point to the bottom of the central device; 'TEL' points to the telephone handset; 'Emission from cable and induction to cable' points to the cables connecting the telephone and the monitor. The text 'K.106(15)\_F6-1' is located in the bottom right corner of the diagram area.
+
+Diagram illustrating the area covered in this Recommendation for interference. A central yellow device (likely a base station or router) is shown with various connections and labels. A red dashed circle indicates the area of concern. Labels include: 'Immunity level of device', 'Emission from device', 'Broadband NW', 'Insufficient installation', 'Failure of connection', 'TEL', 'Emission from cable and induction to cable' (twice), and 'K.106(15)\_F6-1'.
+
+Figure 6-1 – Area covered in this Recommendation
+
+# 7 Relevant requirements
+
+### 7.1 Relevant EMC standards for devices
+
+Devices considered in this Recommendation should comply with relevant international standards, such as: [ITU-T K.74], [IEC CISPR 22], [IEC CISPR 24], [IEC CISPR 32], [IEC 60728-2] and [IEC 60728-12]. If devices do not comply with these standards, the devices shall be tested and checked for their EMC performances.
+
+### 7.2 Regional regulations
+
+In some regions or countries, there are regulations related to interference due to the coexistence of wired telecommunication and radio communication systems. These regional or national regulations should be checked before surveying an interference case between wired telecommunications and radio communications. Examples of these regulations, especially for cable television networks, are given in Appendix II.
+
+# 8 Guidance to identify and address interference
+
+### 8.1 Procedure to identify interference sources
+
+#### 8.1.1 Flowchart
+
+The procedure to reduce interference is shown in the flowchart in Figure 8-1. An interference case is dependent on the surrounding conditions, e.g., the number of devices, the electromagnetic (EM) environment and the distance from the antenna of the radio devices. Therefore, users of this Recommendation should take these conditions into account.
+
+![Flowchart for interference reduction and troubleshooting. The process starts with 'Recognize trouble due to interference', followed by 'Obtain all information about the interference' (which also receives input from 'Phenomenon, timing and period of occurrence, etc.'). It then checks for hardware or software failure. If 'Yes', it proceeds to 'Solve problem' and 'End'. If 'No', it checks the installation (earthing and bonding, cabling). If 'Bad', it proceeds to 'Fix the installation' and then to a 'Problem solved?' decision. If 'Good', it proceeds to 'Check EMC standard compliance'. From 'Problem solved?', if 'Yes', it ends; if 'No', it loops back to 'Check EMC standard compliance'. The next steps are 'Measure the EM environment' (listing performer, quantity, method, procedure) and 'Evaluate results and troubleshoot cause' (listing period of occurrence, specifications, synchronization, other information). A label 'K.106(15)_F8-1' is present near the bottom right.](cfef993dcc8fb513de79eb1f93cf26ae_img.jpg)
+
+```
+
+    graph TD
+      A[Recognize trouble due to interference] --> B[Obtain all information about the interference]
+      C[/Phenomenon, timing and period of occurrence, etc./] --> B
+      B --> D{Check other possibilities  
+- hardware failure?  
+- software failure?}
+      D -- Yes --> E[Solve problem]
+      E --> F([End])
+      D -- No --> G{Check installation  
+- earthing and bonding  
+- cabling}
+      G -- Bad --> H[Fix the installation]
+      H --> I{Problem solved?}
+      I -- Yes --> J([End])
+      I -- No --> K[Check EMC standard compliance]
+      G -- Good --> K
+      K --> L[Measure the EM environment  
+- measurement performer  
+- measurement quantity  
+- measurement method  
+- measurement procedure]
+      L --> M[Evaluate results and troubleshoot cause  
+- period of occurrence  
+- specifications of suspected equipment (clock, etc.)  
+- synchronization between trouble and disturbance  
+- other information, e.g., installation of new equipment]
+  
+```
+
+K.106(15)\_F8-1
+
+Flowchart for interference reduction and troubleshooting. The process starts with 'Recognize trouble due to interference', followed by 'Obtain all information about the interference' (which also receives input from 'Phenomenon, timing and period of occurrence, etc.'). It then checks for hardware or software failure. If 'Yes', it proceeds to 'Solve problem' and 'End'. If 'No', it checks the installation (earthing and bonding, cabling). If 'Bad', it proceeds to 'Fix the installation' and then to a 'Problem solved?' decision. If 'Good', it proceeds to 'Check EMC standard compliance'. From 'Problem solved?', if 'Yes', it ends; if 'No', it loops back to 'Check EMC standard compliance'. The next steps are 'Measure the EM environment' (listing performer, quantity, method, procedure) and 'Evaluate results and troubleshoot cause' (listing period of occurrence, specifications, synchronization, other information). A label 'K.106(15)\_F8-1' is present near the bottom right.
+
+**Figure 8-1 – Interference reduction and troubleshooting flowchart**
+
+#### **8.1.2 Checking for hardware or software failure**
+
+In some cases, an interference problem may cause hardware or software failure. Therefore, the devices should be checked to ensure that they are in a normal operation condition. This can be accomplished by checking or reviewing: operations lamps (e.g., device on/off LED status), logging data, software settings, protocols, error correction (such as forward error correction (FEC)), and placement diversity techniques, etc.
+
+#### **8.1.3 Checking the installation**
+
+Before obtaining information on the EM environment of the surroundings, the installation shall be checked. The following conditions/questions should be checked:
+
+- do the devices and cables comply with relevant international or national standards?
+- is the installation of the cables and/or devices that are connected to the broadband networks appropriate? check the device's user manual for specifications of cables, connectors, etc.
+- is the connection point unstable or faulty?
+- has the cable or the shell of the device been damaged?
+- is the cabling/cable distribution suitable for use in the home?
+
+#### 8.1.4 Checking relevant standards and regulations
+
+All equipment connected to broadband networks should comply with relevant international or national EMC standards. Moreover, radio devices that could be related to interference should also comply with relevant standards and regulations. These compliance checks need to be completed before measurements are carried out. Furthermore, some regions and countries have their own regulations, especially for cable television networks. Any such compliance checks to these regional or country-specific regulations should also be checked before surveying an interference case.
+
+#### 8.1.5 Measurement methods
+
+Fundamental measurement methods for measuring interference cases are given in [ITU-T MTIM]. For interference cases between radio devices and a cable or equipment connected to wired broadband telecommunication networks and/or cable television networks, the use of measurement equipment, such as a vector spectrum analyser, digital demodulation receiver, communication analyser, etc., are helpful to understand the phenomena correctly.
+
+The EM environment should be measured by following these four steps:
+
+- 1) Before measuring the EM environment, all devices that intentionally radiate electromagnetic waves should be turned off in order to reduce intentional electromagnetic radiation. Once this has been completed, the EM environment is measured using appropriate measurement instruments.
+- 2) After step 1 has been completed, all devices that were turned off in step 1 should be turned back on. All devices that are connected to wired broadband networks should then be turned off in order to reduce unintentional emission from the devices.
+- 3) After steps 1 and 2 have been completed, all devices that may be related to interference should be turned off, and the EM environment should be measured again.
+- 4) After step 3 has been completed, the results obtained in the above three steps shall be compared to find out the differences among them.
+
+A description of the EM environment in a home network is given in [ITU-T K.92]; the measurement procedures for the actual EM environment in the home are also presented in Appendix II of [ITU-T K.92]. The disturbance characteristics and levels of the environment in customer premises are described in both [ITU-T K.34] and in clauses 8.3 and A.1 of [IEC 61000-2-5].
+
+#### 8.1.6 Evaluation of measured data
+
+Several quantities obtained by the measurements, such as frequency, signal levels, demodulation data (e.g., eye-pattern, constellation diagram), etc., shall be evaluated.
+
+##### 8.1.6.1 Frequency and signal levels
+
+Intentional radio signals in measured frequency bands should first be checked using standards or information on frequency allocations. For example, Appendix IV gives protection levels for radio communication systems related to safety issues in aeronautical systems. By comparing measured results with frequencies according to the radio frequency (RF) allocation table or reference publications, intentional radio signals can be identified, and their levels, necessary to meet requirements, checked. According to the results from step 1 of clause 8.1.5, the radiation signal from
+
+radio devices should have disappeared. However, if a signal exists at the same frequency that is used by the radio devices in the spectrum, then that signal may be considered as an unintentional emission from a cable or from devices connected to the wired broadband networks, or an intentional radiation emission from the surroundings. Demodulation data of that signal could yield useful information.
+
+Additional measurements should be performed to obtain more detailed information from the interference source.
+
+##### **8.1.6.2 Demodulation data**
+
+Current radio devices mainly use digital modulation techniques. Evaluating the demodulated data can provide additional information about the interference source. For example, if the signal originates from the radio device, the transmission property of the device can be obtained. However, if the signal is unintentionally emitted from the cable or device, then demodulation properties cannot be obtained if modulation is different between the radio device and wired networks. Therefore, it is important to check the modulation method being used in the radio device.
+
+#### **8.1.7 Finding interference sources and part of emission or entry**
+
+Evaluating the information obtained from measurement data and interference phenomena can be used to identify interference sources, and an area and/or a location. After the interference source is determined, the mechanism of the interference should be analysed.
+
+If the source of interference or entry point is not identified from the measurement information, then additional measurements should be carried out to identify the interference source and location.
+
+The following techniques are helpful to distinguish the cause of trouble and single out a disturbance source in the field:
+
+- using a directional antenna;
+- turning on and off the devices one by one;
+- moving a cable or device connected to the wired broadband network;
+- turning off/on radio devices.
+
+Determining the source of interference is the most important step needed to solve or reduce the interference problem.
+
+If the interference source is identified, the interference identification process should be repeated to confirm the results and to determine the coupling path or entry of emission.
+
+### **8.2 Mitigation techniques applied to equipment connected to wired broadband networks and cable television networks**
+
+#### **8.2.1 Measures applied to cables connected to wired broadband networks**
+
+Mitigation techniques for balanced cables are as follows:
+
+- using a shielded cable connected to the earth on both ends or one side, if necessary;
+- attaching a magnetic ring on the cable or inserting a common-mode choke (CMC);
+- inserting a differential-mode filter into the cable;
+
+NOTE – The relationship between a frequency band of transmission signal and of interference source should be taken into consideration when selecting the differential-mode filter in order to reduce the influence of the transmission signal in the cable.
+
+- changing the distribution of the cable or the cable length.
+
+For unbalanced cables, such as coaxial type, mitigation techniques are as follows:
+
+- replacing cables with a double or triple shielded type;
+- attaching a magnetic ring on the cable;
+
+- inserting an isolation transformer.
+
+#### **8.2.2 Measures applied to devices connected to wired broadband networks**
+
+Mitigation measures for devices are as follows:
+
+- moving the device from the original location to another location;
+- installing an electromagnetic shield to the device.
+
+NOTE – Using a metal plate, a conductive paint, or a sheet that includes electromagnetic materials (e.g., carbon powder, ferrite powder) is an effective and easy method used to increase the shielding effect.
+
+# **9 Procedure for selecting appropriate mitigation techniques**
+
+Mitigation measures used to solve interference cases are given in [ITU-T MTIM]. Procedures to mitigate interference are shown in Figure 9-1.
+
+### **9.1 Checking information obtained from the measurement or interference phenomena**
+
+All information obtained from measurement and interference phenomena should be checked. Useful information to be considered is as follows:
+
+- timing of interference and malfunction status of the device experiencing the interference;
+- working mode of the device experiencing the interference and other electric/electronics devices;
+- position of devices, layout of cables and distances among cables;
+- frequency and level of measurement results;
+- analysis and evaluation of measurement results.
+
+### **9.2 Checking radio devices in normal operation and installation**
+
+Before applying mitigation measures, normal operation of the radio devices should be checked again. If a radio device does not work normally, then users of the device should contact the manufacturer. If the radio device is working as intended, then the entire installation, including cables, cabling, devices, connection between cables, or cables and devices, should be rechecked. If any faults or failures are identified, then service personnel or users should attempt to resolve these issues as appropriate.
+
+After the checks and fixes, the interference phenomena should be reconfirmed.
+
+### **9.3 Adding appropriate mitigation measures**
+
+Mitigation measures are given in [ITU-T MTIM]. Countermeasures should be applied near an entry point of disturbance or exit point of unintentional emission. For cables connected to broadband networks, CMC and differential-mode filters should be selected to reduce disturbance effects. For the devices, shielding materials such as metal plates, conductive paint, or sheets made of ferrite or other conductive materials are effective in reducing disturbance effects.
+
+After mitigation has been accomplished, the EM environment should be measured again, in order to check the effectiveness of the mitigation measures.
+
+If the mitigation measures do not provide sufficient effectiveness, then additional measures should be taken.
+
+![Flowchart titled 'Procedure to mitigate an interference problem'. It starts with 'Reviewing EMC troubles/measurement results' and proceeds through checking radio device operation, installation, and combined checks. If 'Bad' at any point, it leads to 'Try to fix or ask manufacturer' or 'Fix installation'. If 'OK', it proceeds to the next check. If 'Interference solved?' is 'Yes', it ends. If 'No', it leads to 'Add measures to the cable or device' or 'Add another measure or try another way'. If 'No mitigation measures to cable or devices' is 'Yes', it lists actions like taking distance, avoiding wired BB-network, or asking the manufacturer. The flowchart is labeled K.106(15)_F9-1.](33ed1f9b27c7c21c797aa928b0f06851_img.jpg)
+
+```
+
+graph TD
+    A[Reviewing EMC troubles/  
+measurement results] --> B{Check radio  
+device in normal  
+operation}
+    B -- Bad --> C[Try to fix or  
+ask manufacturer]
+    C --> B
+    B -- OK --> D{Re-check  
+installation}
+    D -- Bad --> E[Fix installation]
+    E --> F{Interference  
+solved?}
+    F -- No --> G{Combined  
+check of both  
+of them}
+    F -- Yes --> H([End])
+    D -- OK --> G
+    G -- OK --> H
+    G -- Bad --> I[Add measures to the  
+cable or device  
+- CMC, filter, shield, etc]
+    I --> J{Interference  
+solved?}
+    J -- Yes --> H
+    J -- No --> K{No mitigation  
+measures to cable  
+or devices}
+    K -- No --> L[Add another measure  
+or try another way]
+    L --> J
+    K -- Yes --> M["The following actions should be considered:  
+For radio device  
+- Taking sufficient distance  
+- Never use close to wired BB-network  
+For both  
+- Asking manufacturer or service provider"]
+  
+```
+
+K.106(15)\_F9-1
+
+Flowchart titled 'Procedure to mitigate an interference problem'. It starts with 'Reviewing EMC troubles/measurement results' and proceeds through checking radio device operation, installation, and combined checks. If 'Bad' at any point, it leads to 'Try to fix or ask manufacturer' or 'Fix installation'. If 'OK', it proceeds to the next check. If 'Interference solved?' is 'Yes', it ends. If 'No', it leads to 'Add measures to the cable or device' or 'Add another measure or try another way'. If 'No mitigation measures to cable or devices' is 'Yes', it lists actions like taking distance, avoiding wired BB-network, or asking the manufacturer. The flowchart is labeled K.106(15)\_F9-1.
+
+**Figure 9-1 – Procedure to mitigate an interference problem**
+
+# Appendix I
+
+## Examples of interference cases in the field
+
+(This appendix does not form an integral part of this Recommendation.)
+
+### I.1 Example 1: Interference between a mobile phone and a set top box
+
+The following table give examples of the interference between radio devices and cable or equipment such as a set top box (STB) connected to wired broadband networks or cable television networks.
+
+**Table I.1 – Interference between a mobile phone and STB**
+
+| <b>Recognizing interference and obtaining information about the interference</b> |                                                                                                                                                                                                                                                                                               |                                                                                                         |
+|----------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------|
+| Interfered device                                                                | Digital video broadcasting (DVB) STB device                                                                                                                                                                                                                                                   |                                                                                                         |
+| Phenomena and timing                                                             | When the mobile phone makes a phone call, the decoding of the HDTV programme may become unstable (e.g., blue screen for several seconds). When the phone call ends, the HDTV programme is recovered automatically. The reason for this is the close proximity of the mobile phone to the STB. |                                                                                                         |
+| Checking other possibilities                                                     | No hardware or software failures exist.                                                                                                                                                                                                                                                       |                                                                                                         |
+| Checking the installation                                                        | Earthing and bonding                                                                                                                                                                                                                                                                          | OK                                                                                                      |
+|                                                                                  | Cabling                                                                                                                                                                                                                                                                                       | OK. The cabling connected to and around the STB devices are checked and unified into a parallel layout. |
+| Checking EMC standard compliance                                                 | Mobile phone and STB devices are marked with certifications showing national and international EMC standards and radio standard compliance.                                                                                                                                                   |                                                                                                         |
+| Measuring the EM environment                                                     | When the mobile phone makes a phone call, a transmission signal is measured on the 900 MHz band or the 1 800 MHz band, depending on the base station.                                                                                                                                         |                                                                                                         |
+| Evaluating results and finding the cause of trouble                              | The DVB STB malfunctioned when the transmission signal was on the 900 MHz band.                                                                                                                                                                                                               |                                                                                                         |
+
+### I.2 Example 2: Emission from connection at coaxial outlet and plug
+
+In this example, a malfunction occurs on a keyless entry system that uses a 312 MHz radio signal. The malfunction was caused by an emission from the connection point on the coaxial cable that transmits television signals in a frequency band of 310-340 MHz.
+
+Figure I.1 shows the cabling at a subscriber's house. The television signal is transmitted through the coaxial cable from the optical network unit (ONU) of fibre to the home (FTTH) to a TV receiver via the TV signal amplifier in the house. The radio wave is emitted from a connection point of the coaxial outlet and plug. The spectrum of the interfering radio wave outside the house is shown in Figure I.2.
+
+The source of the interfering emission is caused by inferior workmanship on the connection of the coaxial cable to the plug where the outer conductor of the cable does not have connection to the plug, as illustrated in Figure I.3.
+
+![Diagram of a house showing the configuration of telecommunication systems. An FTTH cable enters the house and connects to an ONU. The ONU is connected to a TV amplifier, which is connected to a TV and a TV distribution unit. A coaxial cable runs from the ONU to a coaxial outlet and plug. A radio emission is shown coming from the coaxial outlet and plug. A spectrum analyser is shown outside the house, with a 3 m distance indicated between it and the house.](8fbdfc3d17fb1dae7b2d8f5a287fa9fc_img.jpg)
+
+The diagram illustrates a house with an FTTH cable entering from the left. Inside, the cable connects to an ONU. The ONU is connected to a TV amplifier, which in turn connects to a TV and a TV distribution unit. A coaxial cable runs from the ONU to a coaxial outlet and plug on the exterior wall. A radio emission is depicted as a yellow lightning bolt coming from this plug. Outside the house, a spectrum analyser is shown with a 3 m distance indicated between it and the house. The label 'K.106(15)\_FI.1' is in the bottom right corner.
+
+Diagram of a house showing the configuration of telecommunication systems. An FTTH cable enters the house and connects to an ONU. The ONU is connected to a TV amplifier, which is connected to a TV and a TV distribution unit. A coaxial cable runs from the ONU to a coaxial outlet and plug. A radio emission is shown coming from the coaxial outlet and plug. A spectrum analyser is shown outside the house, with a 3 m distance indicated between it and the house.
+
+**Figure I.1 – Configuration of telecommunication systems in which a radio disturbance occurred (disturbance caused by TV signal from ONU of FTTH)**
+
+![Graph showing Field strength (dBμV/m) versus Frequency (MHz). The Y-axis ranges from 0 to 100 dBμV/m, and the X-axis ranges from 300 to 350 MHz. The graph shows a red line representing the field strength, which is approximately 40 dBμV/m at 300 MHz, drops to about 20 dBμV/m at 310 MHz, rises to about 50 dBμV/m at 320 MHz, drops to about 20 dBμV/m at 330 MHz, rises to about 50 dBμV/m at 340 MHz, and drops to about 20 dBμV/m at 350 MHz.](f4d72193f77f6646a2a1f4baaa927154_img.jpg)
+
+The graph shows the field strength in dBμV/m on the y-axis (0 to 100) against frequency in MHz on the x-axis (300 to 350). The red line shows a signal that is around 40 dBμV/m at 300 MHz, drops to 20 dBμV/m at 310 MHz, rises to 50 dBμV/m at 320 MHz, drops to 20 dBμV/m at 330 MHz, rises to 50 dBμV/m at 340 MHz, and drops to 20 dBμV/m at 350 MHz. The label 'K.106(15)\_FI.2' is in the bottom right corner.
+
+Graph showing Field strength (dBμV/m) versus Frequency (MHz). The Y-axis ranges from 0 to 100 dBμV/m, and the X-axis ranges from 300 to 350 MHz. The graph shows a red line representing the field strength, which is approximately 40 dBμV/m at 300 MHz, drops to about 20 dBμV/m at 310 MHz, rises to about 50 dBμV/m at 320 MHz, drops to about 20 dBμV/m at 330 MHz, rises to about 50 dBμV/m at 340 MHz, and drops to about 20 dBμV/m at 350 MHz.
+
+**Figure I.2 – Radio spectrum of disturbance from coaxial cabling**
+
+![Close-up photograph of a coaxial plug showing inferior workmanship. The plug is white and appears to be poorly assembled, with visible internal components and a rough finish.](41245ac07db266bea228735b9e8c8b73_img.jpg)
+
+This is a close-up photograph of a white coaxial plug. It shows signs of poor workmanship, with visible internal components and a rough, unfinished exterior.
+
+Close-up photograph of a coaxial plug showing inferior workmanship. The plug is white and appears to be poorly assembled, with visible internal components and a rough finish.
+
+**Figure I.3 – Inferior workmanship at coaxial plug**
+
+### I.3 Example 3: Emission from indoor cabling of CS/BS down-converted signal
+
+In this example, a radio disturbance from a coaxial outlet causes the malfunction of a wireless handset of a key telephone system (business telephone system) using a 1.9 GHz digital radio connection.
+
+Figure I.4 shows the configuration of the telecommunication system in which the radio disturbance occurred. The radio signal of the communication satellite (CS)/broadcasting satellite (BS) in the 12 GHz frequency band is converted to an intermediate frequency (IF) of 1-2 GHz at the built-in converter in the parabolic antenna. The IF signals were transmitted from the CS/BS amplifier through the indoor coaxial cable to a CS receiver. The radio disturbance is emitted from the coaxial outlet, shown in Figure I.4, located on the wall.
+
+![Diagram of a telecommunication system configuration showing a radio disturbance. The system includes an ISDN TA connected to an ISDN line and a PBX for home key telephone. The PBX is connected to a FAX on the ground floor and several terminals on the first floor. Two terminals with wireless handsets are shown, with a red starburst indicating a 'Malfunction on wireless links' between them and the PBX. On the right, an antenna is connected to a CS/BS amplifier, which is connected to three CS receivers via coaxial cables. These CS receivers are also connected to coaxial outlets. The diagram is divided into 'First floor' and 'Ground floor' by a dashed line. A label 'K.106(15)_FI.4' is at the bottom right.](76b0cd79baaedd942af4dc42f2e764b8_img.jpg)
+
+ISDN  
+ISDN TA  
+PBX for home key telephone  
+First floor  
+Ground floor  
+FAX  
+Malfunction on wireless links  
+Terminal with wireless handset  
+Terminal with wireless handset  
+Antenna  
+CS/BS amplifier  
+CS receiver  
+CS receiver  
+CS receiver  
+Coaxial cables  
+Coaxial outlet  
+K.106(15)\_FI.4
+
+Diagram of a telecommunication system configuration showing a radio disturbance. The system includes an ISDN TA connected to an ISDN line and a PBX for home key telephone. The PBX is connected to a FAX on the ground floor and several terminals on the first floor. Two terminals with wireless handsets are shown, with a red starburst indicating a 'Malfunction on wireless links' between them and the PBX. On the right, an antenna is connected to a CS/BS amplifier, which is connected to three CS receivers via coaxial cables. These CS receivers are also connected to coaxial outlets. The diagram is divided into 'First floor' and 'Ground floor' by a dashed line. A label 'K.106(15)\_FI.4' is at the bottom right.
+
+**Figure I.4 – Configuration of a telecommunication system in which a radio disturbance occurred (disturbance caused by IF signal of CS/BS antenna)**
+
+# Appendix II
+
+## Examples of regional regulations for cable television networks
+
+(This appendix does not form an integral part of this Recommendation.)
+
+### II.1 Overview
+
+In some regions or countries, there are regulations related to interference due to coexistence of wired telecommunication and radio communication systems. These regional or national regulations should be checked before surveying interference cases between wired telecommunication and radio communication systems.
+
+When cable television commercialization began, there were a number of issues related to interference due to the emissions from cable television coaxial cables to radio communication systems, including aeronautical radios as well as cellular phones. Therefore, it is typical for each region or country to have their own regulations, particularly for cable television systems. In such regulations, cable television operators are obliged to monitor the emission levels, not only from headend systems, but also from customers' premises.
+
+### II.2 Examples of regional regulations
+
+The following clauses provide relevant information on regional regulations.
+
+#### II.2.1 United States FCC CFR 47, 76.605
+
+The following example exemplifies the case of United States, Federal Communications Commission (FCC) extracts from FCC CFR 47, 76.605 [b-FCC CFR 47]:
+
+*§ 76.605 Technical standards.*
+
+*(12) As an exception to the general provision requiring measurements to be made at subscriber terminals, and without regard to the type of signals carried by the cable television system, signal leakage from a cable television system shall be measured in accordance with the procedures outlined in §76.609(h) and shall be limited as follows:*
+
+| Frequencies                                      | Signal leakage limit (micro-volt/meter) | Distance in meters (m) |
+|--------------------------------------------------|-----------------------------------------|------------------------|
+| Less than and including 54 MHz, and over 216 MHz | 15                                      | 30                     |
+| Over 54 and up to and including 216 MHz          | 20                                      | 3                      |
+
+#### II.2.2 Japan
+
+In Japan, regulations for cable broadcast facilities are contained in ordinance No. 83 of Ministry of Internal Affairs and Communications (2011) "Technical requirement on quality of cable broadcast", [b-Japan] as shown below.
+
+*Article 8: The leakage field intensity of a cable broadcast facility shall not be in excess of 0.05 millivolt per meter at a distance of 3 meters from the cable broadcast facility.*
+
+Note that this Article shall apply to any leakage of electric field between cable headend systems and the input ports of customers' premises equipment.
+
+#### II.2.3 China
+
+Currently, there are no specific standards or regulations on the coexistence of cable television and radio communication systems in China, but there are two electromagnetic interference (EMI)/EMC related standards for coaxial cables as follows.
+
+##### II.2.3.1 GY/T 186-2002
+
+Industry Standard GY/T 186-2002 "Specifications and methods of measurement on shielding performance of RF cable used in CATV systems", [b-GY/T 186] specifies the signal shielding performance requirement of coaxial cables, and Table II.1 below is a translation of part of the standard.
+
+**Table II.1 – Shielding performance of RF coaxial cable used in CATV systems**
+
+| No. | Cable types                 | Unit | Frequency | Technical Index       |                         |                     |
+|-----|-----------------------------|------|-----------|-----------------------|-------------------------|---------------------|
+|     |                             |      |           | Shielding attenuation | Shielding effectiveness |                     |
+|     |                             |      |           |                       | Before cable shaking    | After cable shaking |
+| 1   | Double-shield coaxial cable | dB   | 5 MHz     | $\geq 60$             | $\geq 60$               | $\geq 55$           |
+|     |                             |      | 50 MHz    | $\geq 60$             | $\geq 60$               | $\geq 55$           |
+|     |                             |      | 200 MHz   | $\geq 70$             | $\geq 70$               | $\geq 65$           |
+|     |                             |      | 500 MHz   | $\geq 70$             | $\geq 70$               | $\geq 65$           |
+|     |                             |      | 800 MHz   | $\geq 70$             | $\geq 70$               | $\geq 65$           |
+|     |                             |      | 1 000 MHz | –                     | $\geq 70$               | $\geq 65$           |
+| 2   | Triple-shield coaxial cable | dB   | 5 MHz     | $\geq 85$             | $\geq 85$               | $\geq 80$           |
+|     |                             |      | 50 MHz    | $\geq 85$             | $\geq 85$               | $\geq 80$           |
+|     |                             |      | 200 MHz   | $\geq 90$             | $\geq 90$               | $\geq 85$           |
+|     |                             |      | 500 MHz   | $\geq 90$             | $\geq 90$               | $\geq 85$           |
+|     |                             |      | 800 MHz   | $\geq 90$             | $\geq 90$               | $\geq 85$           |
+|     |                             |      | 1 000 MHz | –                     | $\geq 90$               | $\geq 85$           |
+| 3   | Quad-shield coaxial cable   | dB   | 5 MHz     | $\geq 85$             | $\geq 90$               | $\geq 85$           |
+|     |                             |      | 50 MHz    | $\geq 85$             | $\geq 90$               | $\geq 85$           |
+|     |                             |      | 200 MHz   | $\geq 90$             | $\geq 95$               | $\geq 90$           |
+|     |                             |      | 500 MHz   | $\geq 90$             | $\geq 95$               | $\geq 90$           |
+|     |                             |      | 800 MHz   | $\geq 90$             | $\geq 95$               | $\geq 90$           |
+|     |                             |      | 1 000 MHz | –                     | $\geq 95$               | $\geq 90$           |
+
+##### II.2.3.2 GB 13836-2000
+
+Chinese Standard GB 13836-2000 "Cabled distribution systems for television and sound signals – Part 2. Electromagnetic compatibility of equipment", [b-GB 13836], which is based on the earlier edition of [IEC 60728-2], specifies performance requirements and measurement methods of electromagnetic compatibility of equipment, its updated version is pending according to [IEC 60728-2], but tolerance of the signal leakage intensity from coaxial cable or communication systems is out of scope.
+
+This standard deals with performance requirements and measurement methods of electromagnetic compatibility of equipment in cable distribution systems for television and sound signals. It specifies
+
+requirements for maximum allowed radiation, minimum immunity and minimum screening effectiveness, and describes test methods for conformance testing.
+
+This standard applies to the radiation characteristics and immunity to electromagnetic disturbance of active and passive equipment (active and passive coaxial wideband distribution equipment, headend equipment, fibre equipment) for the reception, processing and distribution of television and sound signals. This standard refers to the following parts described in GB/T 6510, which is from interface of the headend, or the other signal source, to the system outlet, or the terminal input port if the system outlet does not exist.
+
+This standard covers the following frequency ranges:
+
+- disturbance voltage injected into the mains 9 kHz to 30 MHz;
+- radiation from active equipment 30 MHz to 25 GHz;
+- immunity of active equipment 150 kHz to 25 GHz;
+- screening effectiveness of passive equipment 30 MHz to 1.75 GHz.
+
+The coaxial cable of cabled distribution systems is out of the scope of this standard.
+
+The requirements of electromagnetic compatibility of any user terminals (e.g., tuners, receivers, decoders, media terminals) are excluded.
+
+**Table II.2 – Radiation from active equipment**
+
+| Frequency range<br>(GHz) | Limit values<br>dB (pW) |
+|--------------------------|-------------------------|
+| 0.03 to 1                | 20                      |
+| 1 to 2.5                 | 43                      |
+| 2.5-25                   | 57                      |
+
+#### II.2.4 European standards related to emission from cable TV systems
+
+##### II.2.4.1 Germany
+
+Cable TV [b-EN 50083-8], not harmonized, contains A-deviations. For example, in Germany for the frequencies according to SchuTSEV (used by security and safety services):
+
+**Table II.3 – Limits for total radiation**
+
+| Frequency range<br>MHz                                                                                                                                                            | Field strength in 3m<br>distance<br>dB( $\mu$ V/m) | Measurement<br>bandwidth<br>kHz | Measurement detector |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------|---------------------------------|----------------------|
+| 30 to 1 000<br>(Note 1)                                                                                                                                                           | 40                                                 | 120                             | Quasi-peak           |
+| 950 to 2 500<br>(Note 2)                                                                                                                                                          | 50                                                 | 1 000                           | Peak                 |
+| 2 500 to 3 500                                                                                                                                                                    | 64                                                 | 1 000                           | Peak                 |
+| NOTE 1 – Applicable for cable TV networks with an upper frequency of 1 000 MHz.<br>NOTE 2 – Applicable for cable TV networks with a lowest frequency of 950 MHz (SAT-IF-Network). |                                                    |                                 |                      |
+
+**Table II.4 – Limits for narrowband radiation**
+
+| Frequency range<br>MHz                                                                                                                                                            | Field strength in 3 m<br>distance<br>dB( $\mu$ V/m) | Measurement<br>bandwidth<br>kHz | Measurement detector |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------|---------------------------------|----------------------|
+| 30 to 1 000<br>(Note 1)                                                                                                                                                           | 27                                                  | 120                             | Quasi-peak           |
+| 950 to 2 500<br>(Note 2)                                                                                                                                                          | 50                                                  | 1'000                           | Peak                 |
+| 2 500 to 3 500                                                                                                                                                                    | 64                                                  | 1'000                           | Peak                 |
+| NOTE 1 – Applicable for cable TV networks with an upper frequency of 1 000 MHz.<br>NOTE 2 – Applicable for cable TV networks with a lowest frequency of 950 MHz (SAT-IF-Network). |                                                     |                                 |                      |
+
+NOTE – The German Administration is against the introduction of limits for a total radiated power, especially as the measurement bandwidth is equivalent to that of narrowband radiation.
+
+##### II.2.4.2 Equipment for CATV
+
+Limits for equipment for CATV (EN 50083-2, harmonized) [b-EN 50083-2] are given in Table II.5 and Table II.6 as follows:
+
+**Table II.5 – Limits for disturbance voltage at the input port for equipment intended for direct connection to receiving antennas**
+
+| Frequency range<br>MHz | Disturbance frequency | Level (75 $\Omega$ )<br>dB( $\mu$ V) |
+|------------------------|-----------------------|--------------------------------------|
+| 30 to 3 000            | Oscillator frequency  | 46                                   |
+| 30 to 3 000            | Oscillator harmonics  | 46                                   |
+| 30 to 3 000            | Other frequencies     | 46                                   |
+
+**Table II.6 – Limits for the radiated power**
+
+| Frequency range<br>MHz                                                                                              | Limits<br>dB (pW)              | Measurement<br>bandwidth<br>kHz | Detector   |
+|---------------------------------------------------------------------------------------------------------------------|--------------------------------|---------------------------------|------------|
+| 5 to 30                                                                                                             | 27 to 20<br>(Notes 1) (Note 2) | 9                               | Quasi-peak |
+| 5 to 30                                                                                                             | 33<br>(Note 3)                 | 9                               | Quasi-peak |
+| 30 to 1 000<br>(Note 4)                                                                                             | 20                             | 120                             | Quasi-peak |
+| 950 to 2 500<br>(Note 5)                                                                                            | 43                             | 1 000                           | peak       |
+| <b>2 500 to 25 000</b>                                                                                              | <b>57</b>                      | <b>peak</b>                     |            |
+| NOTE 1 – Decreasing linear with the logarithm of the frequency.<br>NOTE 2 – For not mains powered active equipment. |                                |                                 |            |
+
+**Table II.6 – Limits for the radiated power**
+
+| Frequency range<br>MHz                                                  | Limits<br>dB (pW) | Measurement<br>bandwidth<br>kHz | Detector |
+|-------------------------------------------------------------------------|-------------------|---------------------------------|----------|
+| NOTE 3 – For mains powered equipment.                                   |                   |                                 |          |
+| NOTE 4 – Applicable for equipment with an upper frequency of 1 000 MHz. |                   |                                 |          |
+| NOTE 5 – Applicable for equipment with a lowest frequency of 950 MHz    |                   |                                 |          |
+
+##### II.2.4.3 Broadcast receiver
+
+Limits for broadcast receiver equipment (EN 55013, harmonized) [b-EN 55013] are given in Table II.7 as follows:
+
+**Table II.7 – Limits for radiated disturbances at 3 m distance**
+
+| Receiver type                                                                                                                                                                                                                                                                                                                                                       | Disturbance<br>source | Frequency<br>range<br>MHz | Limits Quasi-peak<br>dB(μV/m) | Limits<br>AV-RMS<br>dB(μV/m)<br>(Note 1) |
+|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------|---------------------------|-------------------------------|------------------------------------------|
+| TV receivers,<br>video recorders<br>and personal<br>computer (PC)<br>tuner cards                                                                                                                                                                                                                                                                                    | Oscillator            | ≤ 1 000                   | fundamental 57                | fundamental 57                           |
+|                                                                                                                                                                                                                                                                                                                                                                     |                       | 30 to 300                 | harmonics 52                  | harmonics 52                             |
+|                                                                                                                                                                                                                                                                                                                                                                     |                       | 300 to 1 000              | harmonics 56                  | harmonics 56                             |
+|                                                                                                                                                                                                                                                                                                                                                                     | Others                | 30 to 230                 | 40                            | (Note 2) 34/40                           |
+| TV and audio<br>broadcast satellite<br>receivers<br>Infrared remote<br>control<br>Infrared<br>headphones                                                                                                                                                                                                                                                            | Others                | 230 to 1 000              | 47                            | 47                                       |
+|                                                                                                                                                                                                                                                                                                                                                                     |                       | 30 to 230                 | 40                            | (Note 2) 34/40                           |
+|                                                                                                                                                                                                                                                                                                                                                                     |                       | 230 to 1 000              | 47                            | 47                                       |
+| FM audio<br>broadcast<br>receivers and PC<br>tuner cards                                                                                                                                                                                                                                                                                                            | Oscillator            | ≤ 1 000                   | fundamental 60                | fundamental 60                           |
+|                                                                                                                                                                                                                                                                                                                                                                     |                       | 30 to 300                 | harmonics 52                  | harmonics 52                             |
+|                                                                                                                                                                                                                                                                                                                                                                     |                       | 300 to 1 000              | harmonics 56                  | harmonics 56                             |
+|                                                                                                                                                                                                                                                                                                                                                                     | Others                | 30 to 230                 | 40                            | (Note 2) 34/40                           |
+|                                                                                                                                                                                                                                                                                                                                                                     |                       | 230 to 1 000              | 47                            | 47                                       |
+| NOTE 1 – The AV-RMS limits can be used as an alternative to the quasi-peak limits.                                                                                                                                                                                                                                                                                  |                       |                           |                               |                                          |
+| NOTE 2 – For narrowband disturbances, the limit is 40 dB(μV/m). For this purpose, a narrowband disturbance is identified if the deviation between peak level and AV-RMS level is < 3 dB. All other signals shall be considered as broadband disturbances. For these signals apply the AV-RMS limit of 34 dB(μV/m) and additional a quasi-peak limit of 54 dB(μV/m). |                       |                           |                               |                                          |
+
+# Appendix III
+
+## Examples of measured emissions from coaxial cables and connectors
+
+(This appendix does not form an integral part of this Recommendation.)
+
+### III.1 Introduction
+
+This appendix presents examples of emission levels measured for different types of coaxial cables and connectors. Results obtained from three types of coaxial cables and two types of connectors are compared. The results indicate that in order to avoid interference to radio services, it is necessary to check its cabling before it is used.
+
+### III.2 Measurement set-up
+
+Figure III.1 shows the set-up for measuring emissions from coaxial cables and connectors.
+
+- the measurement was carried out in an anechoic chamber;
+- the coaxial cable was set at a height of 1 m and had a length of 5 m;
+- the inner and outer conductors were terminated by resistance of 75 ohms;
+- the outer conductor was connected to a ground by resistance of 150 ohms in order to stabilize common-mode impedance;
+- the antenna was set at the near-end of the cable, at a distance of 3 m.
+
+The horizontal and vertical components of the electromagnetic fields were measured.
+
+![Figure III.1: Configuration for measurement of emissions from coaxial cables. (a) Elevation view shows a 5 m coaxial cable at 1 m height connected to a signal generator and terminated with 75 Ω. A 150 Ω resistor connects the outer conductor to the reference earth plane. Point B is at the cable's bend. (b) Plan view shows the cable's length and the antenna's position at 3 m distance and 1 m height.](9167fa5ebcb66516d1bbb421ec9bba7b_img.jpg)
+
+The diagram illustrates the measurement setup in two views: (a) Elevation and (b) Plan. In (a) Elevation, a 5 m long coaxial cable is shown at a height of 1 m above a reference earth plane. The cable is connected to a signal generator at one end and terminated with a 75 Ω coaxial termination at the other. A 150 Ω resistor is connected between the outer conductor and the earth plane at the termination end. Point B is marked at the bend of the cable. In (b) Plan, the cable is shown from above, with its length of 5 m indicated. An antenna, 1 m high, is positioned at a distance of 3 m from the near end of the cable. Point B is also marked in this view.
+
+Figure III.1: Configuration for measurement of emissions from coaxial cables. (a) Elevation view shows a 5 m coaxial cable at 1 m height connected to a signal generator and terminated with 75 Ω. A 150 Ω resistor connects the outer conductor to the reference earth plane. Point B is at the cable's bend. (b) Plan view shows the cable's length and the antenna's position at 3 m distance and 1 m height.
+
+Figure III.1 – Configuration for measurement of emissions from coaxial cables
+
+### III.3 Measurement result
+
+#### III.3.1 Emission from coaxial cables
+
+Emissions from three kinds of cable, i.e., 5C-2V, 5C-2W and S-5C-FB, were measured. Results of vertical and horizontal polarizations are shown in Figure III.2 and Figure III.3, respectively.
+
+![Figure III.2: Frequency dependency of emission for different structures of coaxial cable (vertical polarization). The graph plots emission level in dBμV/m against frequency in MHz on a log-log scale. The y-axis ranges from -50 to 120 dBμV/m, and the x-axis ranges from 10 to 10,000 MHz. Four data series are shown: System noise (grey), 5C-2V (green), 5C-2W (blue), and S-5C-FB (red). The noise floor is around -20 dBμV/m. The 5C-2V cable shows the highest emission, peaking near 70 dBμV/m at 2,000 MHz. The 5C-2W and S-5C-FB cables show similar emission levels, peaking around 50 dBμV/m at 2,000 MHz.](645bea0b27d63e4a9a300af5793ae7d2_img.jpg)
+
+Figure III.2 is a line graph showing the frequency dependency of emission for different structures of coaxial cable under vertical polarization. The y-axis is labeled "Emission level when input signal level is 0 dBm [dBμV/m]" and ranges from -50 to 120 in increments of 10. The x-axis is labeled "Frequency [MHz]" and is logarithmic, with major ticks at 10, 100, 1,000, and 10,000. The graph includes four data series: "System noise" (grey line), "5C-2V" (green line), "5C-2W" (blue line), and "S-5C-FB" (red line). The system noise is relatively flat around -20 dBμV/m. The 5C-2V cable shows the highest emission levels, starting around 40 dBμV/m at 100 MHz and rising to about 70 dBμV/m at 2,000 MHz. The 5C-2W and S-5C-FB cables show similar emission levels, starting around 10 dBμV/m at 100 MHz and rising to about 50 dBμV/m at 2,000 MHz. A label "K.106(15)\_FIII.2" is present in the bottom right corner.
+
+Figure III.2: Frequency dependency of emission for different structures of coaxial cable (vertical polarization). The graph plots emission level in dBμV/m against frequency in MHz on a log-log scale. The y-axis ranges from -50 to 120 dBμV/m, and the x-axis ranges from 10 to 10,000 MHz. Four data series are shown: System noise (grey), 5C-2V (green), 5C-2W (blue), and S-5C-FB (red). The noise floor is around -20 dBμV/m. The 5C-2V cable shows the highest emission, peaking near 70 dBμV/m at 2,000 MHz. The 5C-2W and S-5C-FB cables show similar emission levels, peaking around 50 dBμV/m at 2,000 MHz.
+
+**Figure III.2 – Frequency dependency of emission for different structures of coaxial cable (vertical polarization)**
+
+![Figure III.3: Frequency dependency of emission for different structures of coaxial cable (horizontal polarization). The graph plots emission level in dBμV/m against frequency in MHz on a log-log scale. The y-axis ranges from -50 to 120 dBμV/m, and the x-axis ranges from 10 to 10,000 MHz. Four data series are shown: System noise (grey), 5C-2V (green), 5C-2W (blue), and S-5C-FB (red). The noise floor is around -20 dBμV/m. The 5C-2V cable shows the highest emission, peaking near 55 dBμV/m at 2,000 MHz. The 5C-2W and S-5C-FB cables show similar emission levels, peaking around 45 dBμV/m at 2,000 MHz.](5500ab73cf84ccc0055eecf28889b4db_img.jpg)
+
+Figure III.3 is a line graph showing the frequency dependency of emission for different structures of coaxial cable under horizontal polarization. The axes and data series are identical to Figure III.2. The y-axis ranges from -50 to 120 dBμV/m, and the x-axis ranges from 10 to 10,000 MHz. The system noise is around -20 dBμV/m. The 5C-2V cable shows the highest emission levels, starting around 20 dBμV/m at 100 MHz and rising to about 55 dBμV/m at 2,000 MHz. The 5C-2W and S-5C-FB cables show similar emission levels, starting around 0 dBμV/m at 100 MHz and rising to about 45 dBμV/m at 2,000 MHz. A label "K.106(15)\_FIII.3" is present in the bottom right corner.
+
+Figure III.3: Frequency dependency of emission for different structures of coaxial cable (horizontal polarization). The graph plots emission level in dBμV/m against frequency in MHz on a log-log scale. The y-axis ranges from -50 to 120 dBμV/m, and the x-axis ranges from 10 to 10,000 MHz. Four data series are shown: System noise (grey), 5C-2V (green), 5C-2W (blue), and S-5C-FB (red). The noise floor is around -20 dBμV/m. The 5C-2V cable shows the highest emission, peaking near 55 dBμV/m at 2,000 MHz. The 5C-2W and S-5C-FB cables show similar emission levels, peaking around 45 dBμV/m at 2,000 MHz.
+
+**Figure III.3 – Frequency dependency of emission for different structures of coaxial cable (horizontal polarization)**
+
+The results indicate that:
+
+- the emission levels from S-5C-FB and 5C-2W are nearly the same;
+
+- below 300 MHz, the emission levels of vertically and horizontally polarized radio wave from 5C-2V cables are greater than those of the other types of cables by 10 to 25 dB and 20 dB for vertically and horizontally polarized waves, respectively;
+- there is no noticeable difference between the three cables above 500 MHz because the shielding effect may be affected by very small windows in the cable's outer conductor.
+
+#### III.3.2 Emissions caused by cable connectors
+
+The measurement configuration is as shown in Figure III.1, but with a coaxial outlet, as shown in Figure III.4, and one of the three cases of plug types shown in Table III.1 inserted in the coaxial cable at point B.
+
+Two types of plugs for coaxial cables were used to determine the dependency of the emission level on the plug structure. The type 1 plug has coaxial structure and the type 2 plug has a structure in which the inner conductor is retained by a set screw and the outer conductor by a spring fixture, as shown in Table III.1.
+
+Emissions were also measured when the outer conductor is not connected to the type 2 plug, which is shown as case 3 in Table III.1, to allow consideration of the case where there is a defect in the coaxial cabling.
+
+![Photograph of a white coaxial outlet with a red label '電通端子' (Electrical Communication Terminal) and a threaded base.](23ccc57a4e09b138c310d1d174c5f316_img.jpg)
+
+A photograph of a white, square-shaped coaxial outlet. The outlet has a central circular opening with a metallic inner sleeve. A small red rectangular label with white Chinese characters '電通端子' (Electrical Communication Terminal) is affixed to the top right corner of the white plastic housing. The bottom of the outlet features a threaded metal base for mounting.
+
+Photograph of a white coaxial outlet with a red label '電通端子' (Electrical Communication Terminal) and a threaded base.
+
+Figure III.4 – Photograph of a coaxial outlet
+
+**Table III.1 – Plugs for coaxial cabling in home environment used in the test**
+
+| Case | Plug type                        | Photo of exterior                                                                                                                                                                            | Photo of interior                                                                                                                                                                                                                                      | Drawing of structure                                                                                                                                                                                                |
+|------|----------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 1    | Type 1                           | <img alt="Exterior photo of a Type 1 coaxial plug, showing a metal F-type connector attached to a black cable." data-bbox="443 338 684 483" src="504fb6a53262b5e01e8deabace06d09e_img.jpg"/> |                                                                                                                                                                                                                                                        | <img alt="Diagram of a Type 1 plug structure showing the assembly of the connector components onto the cable end." data-bbox="1050 338 1455 416" src="ee90b672a9d20249c450ba494585670f_img.jpg"/>                   |
+| 2    | Type 2                           | <img alt="Exterior photo of a Type 2 coaxial plug, which is a white plastic rectangular connector." data-bbox="443 528 684 696" src="407deb4883d59e336bec74d6ad938feb_img.jpg"/>             | <img alt="Interior photo of a Type 2 plug showing the internal wiring where the cable's inner conductor is secured by a screw and the outer conductor by a spring clip." data-bbox="691 528 1046 808" src="46b3d80e0eefc5b607b53dc87b233f96_img.jpg"/> | <img alt="Diagram of Type 2 plug structure with labels: 'Screw fixing for inner conductor' and 'Spring fixing for outer conductor'." data-bbox="1066 539 1455 842" src="5f28d893bdf2f13d6e21bfa5b2e83d6c_img.jpg"/> |
+| 3    | Outer conductor is not connected | <img alt="Exterior photo of a Type 2 plug, identical in appearance to Case 2." data-bbox="443 898 684 1066" src="13d8b0bce3fc54896403a224391e6340_img.jpg"/>                                 | <img alt="Interior photo of a Type 2 plug where the outer conductor of the cable is visibly disconnected from the internal spring clip." data-bbox="691 898 1046 1178" src="8c5c051321f231c17866c3b2005959cf_img.jpg"/>                                | <img alt="Diagram of Type 2 plug structure with labels: 'Screw fixing for inner conductor' and 'Outer conductor is disconnected'." data-bbox="1066 909 1455 1189" src="c6724ed9434df36d3fcc74576889d691_img.jpg"/>  |
+
+Measurement results of vertical and horizontal polarizations are shown in Figure III.2 and Figure III.3, respectively. Comparing these results, the following points are summarized:
+
+- The emission of vertically polarized electromagnetic waves from cables with the type 1 plug is almost completely the same as that from coaxial cables without any connector in the measured frequency range. The emission of horizontally polarized electromagnetic waves with the type 1 plug is also about the same as that with no connector below 100 MHz, but it is about 10 dB greater above 200 MHz.
+- The emission of vertically and horizontally polarized waves from cabling with a type 2 plug is from 30 to 40 dB higher than that without connectors over the whole measured frequency range. This may be caused by emissions from the exposed open loop formed by the screw fixing of the inner conductor. Electromagnetic waves are also emitted by the longitudinal current in the outer conductor of the coaxial cable excited by a longitudinal electromotive force caused by the inductance at the screw-fixed part of the plug.
+- When the outer conductor of the coaxial cable is not connected to the plug, e.g., in case an installation failure may exist in the fields, the emission level reaches 80 dB $\mu$ V/m to 100 dB $\mu$ V/m over the entire measured frequency range. This may cause interference to radio services close to the cabling.
+
+## Appendix IV
+
+## Information of radio communication systems related to safety issues
+
+(This appendix does not form an integral part of this Recommendation.)
+
+Several radio communication systems strongly relate to safety issues. For example, aeronautical radio systems are sensitive when interference occurs. Thus, usage of the radio communication systems and an influence of disturbance should take into consideration when surveying interference cases. This appendix gives information of radio communication related to safety. Information in this appendix will be updated in future.
+
+### IV.1 Radio communication related to aeronautical systems
+
+Table IV.1 shows the required level of protection for aeronautical systems operating between 190 kHz and 1 215 MHz. This information is given from ITU-R Working Party 5B (WP5B).
+
+**Table IV.1 – The required level of protection for aeronautical systems operating between 190 kHz and 1 215 MHz**
+
+| Frequency band            | System                                  | Receiver location   | Receiver protection criteria reference                                   |
+|---------------------------|-----------------------------------------|---------------------|--------------------------------------------------------------------------|
+| 190-850 kHz               | Area navigation (NDB)                   | Airborne            | ICAO Document 9718, Chapter 9, Table 9-1 – General Protection Limits     |
+| 2.85-22 MHz               | HF communications                       | Airborne/<br>Ground | ICAO Document 9718, Chapter 9, Table 9-1 – General Protection Limits     |
+| 74.8-75.2 MHz             | Approach navigation (ILS marker beacon) | Airborne            | ICAO Document 9718, Chapter 9, Table 9-1 – General Protection Limits     |
+| 108-117.975 MHz           | Approach navigation (ILS localizer)     | Airborne            | ICAO Document 9718, Chapter 9, Table 9-1 – General Protection Limits     |
+| 108-117.975 MHz           | Area navigation (VOR)                   | Airborne            | ICAO Document 9718, Chapter 9, Table 9-1 – General Protection Limits     |
+| 117.975-137 MHz & 243 MHz | VHF communications                      | Airborne/<br>Ground | ICAO Document 9718, Chapter 9, Table 9-1 – General Protection Limits     |
+| 328.6-335.4 MHz           | Approach/Landing (ILS glide path)       | Airborne            | ICAO Document 9718, Chapter 9, Table 9-1 – General Protection Limits     |
+| 960-1 215 MHz             | Area navigation (DME)                   | Ground              | ICAO Document 9718, Chapter 9, Table 9-1 – General Protection Limits     |
+| 978 MHz                   | Area navigation (UAT)                   | Airborne/<br>Ground | ICAO Annex 10, Vol. III, Chapter 12, section 12.3.2 – Receiving Function |
+| 1 030 & 1 090 MHz         | Area navigation (SSR)                   | Airborne/<br>Ground | ICAO Document 9924, Appendix D, Table D-3 – Downlink Margin              |
+
+# Bibliography
+
+- [b-EN 50083-2] EN 50083-2:2012, *Cable networks for television signals, sound signals and interactive services. Electromagnetic compatibility for equipment.*
+- [b-EN 50083-8] EN 50083-8:2013, *Cable networks for television signals, sound signals and interactive services. Electromagnetic compatibility for networks.*
+- [b-EN 55013] EN 55013:2013, *Sound and television broadcast receivers and associated equipment. Radio disturbance characteristics. Limits and methods of measurement.*
+- [b-FCC CFR 47] FCC CFR 47, 76.605, USA.
+- [b-GB 13836] GB 13836-2000, *Cabled distribution systems for television and sound signals – Part 2. Electromagnetic compatibility of equipment*, China.
+- [b-GY/T 186] GY/T 186-2002, *Specifications and methods of measurement on shielding performance of RF cable used in CATV systems*, China.
+- [b-ICAO 9718] ICAO Document Doc 9718, *Handbook on Radio Frequency Spectrum Requirements for Civil Aviation (Volume I, ICAO spectrum strategy, policy statements and related information)*. 2014.
+- [b-ICAO 9924] ICAO Document Doc 9924, *Aeronautical Surveillance Manual*. 2010.
+- [b-ICAO Annex 10] ICAO Annex 10 Vol III, *Aeronautical Telecommunications - Volume III Communications Systems (Part I - Digital Data Communications Systems)*. 2014.
+- [b-Japan] Ordinance No. 83 of Ministry of Internal Affairs and Communications (2011), *Technical requirement on quality of cable broadcast* (in Japanese).
+
+
+
+
+
+## **SERIES OF ITU-T RECOMMENDATIONS**
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | General tariff principles                                                                                                                                 |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| Series G        | Transmission systems and media, digital systems and networks                                                                                              |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| <b>Series K</b> | <b>Protection against interference</b>                                                                                                                    |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| Series P        | Terminals and subjective and objective assessment methods                                                                                                 |
+| Series Q        | Switching and signalling                                                                                                                                  |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects and next-generation networks                                                                 |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |

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+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**K.108**
+
+(11/2015)
+
+SERIES K: PROTECTION AGAINST INTERFERENCE
+
+---
+
+**Joint use of poles by telecommunication and  
+solidly earthed power lines**
+
+Recommendation ITU-T K.108
+
+ITU-T
+
+![ITU logo](84a1d09fb489061482111515543b60dc_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a stylized globe with a red lightning bolt striking through it. The letters "ITU" are prominently displayed in blue and red.
+
+ITU logo
+
+International  
+Telecommunication  
+Union
+
+
+
+# Recommendation ITU-T K.108
+
+# Joint use of poles by telecommunication and solidly earthed power lines
+
+## Summary
+
+Recommendation ITU-T K.108 provides protective procedures against accidental contacts between power lines and telecommunication lines, when these lines use the same poles. These procedures are primarily intended to reduce the risk of an accidental contact (power-cross). However, in the case of a power cross, the protective procedures mitigate its consequences. This Recommendation provides a set of clearance values between power and telecommunication lines at the joint-use pole and the rules for achieving the insulation coordination between the lines. In the case of a power-cross, the earthing and bonding procedures are intended to assure the immediate tripping of the power line circuit breaker. As a backup protection, this Recommendation requires the use of surge protective devices at the customer premises whenever there is a joint-use of poles with medium voltage power lines.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T K.108    | 2015-11-29 | 5           | <a href="http://handle.itu.int/11.1002/1000/12671">11.1002/1000/12671</a> |
+
+## Keywords
+
+Clearances, earthing, insulation coordination, joint-use of poles, power-cross, power lines.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2016
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                                          | Page |
+|--------------------------------------------------------------------------|------|
+| 1 Scope.....                                                             | 1    |
+| 2 References.....                                                        | 1    |
+| 3 Definitions .....                                                      | 2    |
+| 3.1 Terms defined elsewhere .....                                        | 2    |
+| 3.2 Terms defined in this Recommendation.....                            | 2    |
+| 4 Abbreviations and acronyms .....                                       | 2    |
+| 5 General considerations.....                                            | 3    |
+| 6 Possible protection approaches.....                                    | 3    |
+| 6.1 Integrated protection.....                                           | 3    |
+| 6.2 Coordinated protection .....                                         | 3    |
+| 7 The power-cross problem .....                                          | 3    |
+| 8 Minimum clearances.....                                                | 4    |
+| 9 Installation of surge protective devices .....                         | 5    |
+| 10 Insulation coordination .....                                         | 6    |
+| 10.1 Insulation of the telecommunication cable outer sheath .....        | 6    |
+| 10.2 Insulation of splices and distribution boxes .....                  | 6    |
+| 10.3 Insulation between the metallic supporting strand and the pole..... | 6    |
+| 11 Bonding and earthing.....                                             | 7    |
+| 11.1 Bonding .....                                                       | 7    |
+| 11.2 Earthing .....                                                      | 8    |
+| Appendix I – Rationale for the insulation coordination.....              | 10   |
+| Bibliography.....                                                        | 12   |
+
+
+
+# Recommendation ITU-T K.108
+
+## Joint use of poles by telecommunication and solidly earthed power lines
+
+## 1 Scope
+
+This Recommendation provides technical procedures in order to protect the telecommunication lines installed in poles that are also used by solidly earthed power distribution lines, with special reference to the accidental contact between these lines (power-cross). For the protection regarding the interference produced by electric power lines on telecommunication lines, the user shall refer to [[b-ITU-T K.26](#)].
+
+The telecommunication lines considered are those made of cables containing one or more twisted metallic pairs with and without a metallic sheath and covered by an outer plastic sheath. These cables are supported by a steel or composite strand that may be incorporated in the same cable or may be independent. In the latter case, the steel strand may be bare or insulated by a plastic outer sheath, and the telecommunication cable is attached to the steel strand usually by a lashing wire.
+
+The power distribution lines considered are those operating in alternating currents with nominal voltages up to 25 kV (phase-to-phase). The lines may have one, two, or three phases, with and without a neutral conductor. It is considered that the power transformer at the distribution substation has its windings in the secondary side connected in Y configuration and that the neutral of the transformer (central point of the Y) is connected directly to earth (solidly earthed). Substation power transformers which are secondary side-earthed through a resistor, non-earthed, or earthed by resonant systems (e.g., Petersen coil) are out of the scope of this Recommendation.
+
+NOTE – The distribution substation referred above is the origin of the distribution medium voltage feeders that provide power to the medium voltage / low voltage transformers.
+
+## 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [[ITU-T K.20](#)] Recommendation ITU-T K.20 (2015), *Resistibility of telecommunication equipment installed in a telecommunications centre to overvoltages and overcurrents*.
+- [[ITU-T K.21](#)] Recommendation ITU-T K.21 (2015), *Resistibility of telecommunication equipment installed in customer premises to overvoltages and overcurrents*.
+- [[ITU-T K.45](#)] Recommendation ITU-T K.45 (2015), *Resistibility of telecommunication equipment installed in the access and trunk networks to overvoltages and overcurrents*.
+- [[ITU-T K.65](#)] Recommendation ITU-T K.65 (2011), *Overvoltage and overcurrent requirements for termination modules with contacts for test ports or surge protective devices*.
+- [[ITU-T K.66](#)] Recommendation ITU-T K.66 (2011), *Protection of customer premises from overvoltages*.
+
+- [IEC 60060-1] IEC 60060-1 (2010), *High-voltage test techniques – Part 1: General definitions and test requirements*.
+- [IEC 61643-21] IEC 61643-21 (2008), *Low voltage surge protective devices – Part 21: Surge protective devices connected to telecommunications and signalling networks – Performance requirements and testing methods*.
+
+## 3 Definitions
+
+### 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 breakdown voltage** [b-IEC 60050]: Voltage at which electric breakdown occurs under prescribed test conditions, or in use.
+
+**3.1.2 insulation coordination** [b-IEC 60050]: Selection of the electric strength of equipment in relation to the voltages which can appear on the system for which the equipment is intended, and taking into account the service environment and the characteristics of the available protective devices.
+
+**3.1.3 low voltage** [b-IEC 60050]: Voltage having a value below a conventionally adopted limit.
+
+NOTE – For the distribution of AC electric power, the upper limit is generally accepted to be 1000 V.
+
+**3.1.4 medium voltage (MV)** [IEC 60050-601:2001, 601-01-28]: (not used in the UK in this sense, nor in Australia). Any set of voltage levels lying between low and high voltage.
+
+NOTE 1 – The boundaries between medium and high voltage levels overlap and depend on local circumstances and history or common usage. Nevertheless the band 30 kV to 100 kV frequently contains the accepted boundary.
+
+NOTE 2 – The medium voltage is not a standardized term. It is specified as a system voltage class by IEEE [b-Terms].
+
+NOTE 3 – The preferred medium nominal (line-to-line) voltages in North America: 4.16 kV, 12.46 kV, 13.8 kV, 34.5 kV and 69 kV [b-Terms]. Typical MV system voltages for public distribution: in Europe 10 kV (mainly underground) 20 kV and 35 kV (mainly overhead) [b-Lacroix], in Japan 6.6 kV.
+
+**3.1.5 solidly earthed (neutral) system** [b-IEC 60050]: A system whose neutral point(s) is(are) earthed directly.
+
+**3.1.6 withstand voltage** [b-IEC 60050]: Voltage applied to a specimen under prescribed test conditions which does not cause breakdown.
+
+### 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following term:
+
+**3.2.1 power-cross**: line-to-earth short-circuit in a power line whose current path to earth involves a telecommunication line.
+
+## 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+SPD Surge Protective Device
+
+V<sub>E</sub> Phase-to-earth voltage of the power line
+
+## 5 General considerations
+
+Telecommunication operators that wish to use the poles already in use for power distribution lines are recommended, when national laws and regulations permit such an arrangement, to take the following general considerations into account:
+
+- There are economic and aesthetic advantages to be derived from the joint-use of poles by telecommunication operators and power utilities.
+- When suitable joint construction methods are used, there is, nevertheless, some increased likelihood of danger by comparison with non-joint-use lines, both to staff working on the telecommunication line and to the telecommunication installation connected thereto. Special training of personnel working on such lines is highly desirable, especially when the nominal power line voltage is above 1 kV.
+- Special formal agreements are desirable between the telecommunication operator and the power utility in the case of joint-use of poles, in order to define responsibilities.
+- Joint-use of poles with power lines having nominal voltages above 25 kV is not recommended.
+
+## 6 Possible protection approaches
+
+In order to protect the telecommunication lines against the likelihood of accidental contact with the directly-earthed power distribution lines in joint-use of poles (power-cross), there are two distinct approaches, which are briefly described in this clause.
+
+### 6.1 Integrated protection
+
+In this approach, the telecommunication operator and the power utility develop together a set of procedures to be applied in both networks in order to achieve the desired level of protection against power-crosses. The resulting procedures may involve the joint-use of earthing connections and the bonding between metallic conductors of both lines (e.g., to bond the telecommunication line supporting strand to the power line neutral conductor). As this approach has to take into account the specificities of both networks, it is not considered in this Recommendation.
+
+NOTE – This approach is used in North America, based on a comprehensive study that settled the procedures and responsibilities for both networks.
+
+### 6.2 Coordinated protection
+
+In this approach, the telecommunication operator implements the protection procedures while taking into account some relevant parameters of the power line, but does not integrate its network with the power network. The resulting procedures do not involve the joint-use of earth connections nor the bonding between metallic conductors of both lines. This Recommendation considers this approach, where the characteristics of the power line are used in order to develop the protection procedures of the telecommunication line in joint-use of poles, resulting in a coordinated protection scheme.
+
+## 7 The power-cross problem
+
+The main source of danger in a joint-use installation between telecommunication and solidly earthed power lines is the power-cross, i.e., the accidental contact between the power line and the telecommunication line. As the power system is directly earthed, a power-cross leads to a very high short-circuit current. The power-cross may take place due to a number of reasons, some of which are summarized below:
+
+- The clearance between the lines is too small, so that an overload on the power conductor reduces its height (sag) and causes a contact with the telecommunication line installed below. This type of power-cross is more likely to involve low voltage power lines.
+
+- The power conductor breaks and falls on the telecommunication line. This type of power-cross is more common in rural areas, due to the longer spans used.
+- The power line insulation fails and leads to a current path involving the telecommunication line. The insulation may fail due to several reasons, such as: cracks or pollution on the insulator, objects falling across the insulator (e.g., tree branches), and lightning surges. This type of power-cross is more likely to involve medium voltage power lines installed on conductive poles (e.g., concrete poles with steel framework).
+
+Figure 1 shows an example of power-cross due to the failure of the power line insulator. The line is typically a medium voltage distribution line (e.g., 15 kV nominal voltage) and the pole is conductive (e.g., concrete with steel reinforcement). In this figure, the electric arc formed across the insulator conducts the current to earth through the pole steel core and part of this current flows through the telecommunication line that is attached to the pole. It is worth mentioning that the insulation provided by the concrete cover is negligible, so that there is little difference between a steel-reinforced pole and a metallic pole from the power-cross point of view. If the insulation failure is caused by a lightning surge, the power frequency current will follow the arc formed by lightning and may keep it on until the power line is switched off.
+
+![Diagram illustrating a power-cross due to insulation failure. A vertical pole is shown with a crossarm support at the top. Three power conductors, labeled 'Phase', are mounted on the crossarm. An 'Electric arc' is shown between one of the phases and the crossarm support. The pole itself is labeled 'Steel reinforcement'. A 'Telecommunication cable' is attached to the side of the pole, below the crossarm support.](349ca0a6a9c2e2651a4deeeaf8be6da1_img.jpg)
+
+Diagram illustrating a power-cross due to insulation failure. A vertical pole is shown with a crossarm support at the top. Three power conductors, labeled 'Phase', are mounted on the crossarm. An 'Electric arc' is shown between one of the phases and the crossarm support. The pole itself is labeled 'Steel reinforcement'. A 'Telecommunication cable' is attached to the side of the pole, below the crossarm support.
+
+**Figure 1 – Example of power-cross due to insulation failure**
+
+## 8 Minimum clearances
+
+In order to reduce the likelihood of power-cross due to the proximity between the lines, a minimum clearance shall be maintained between the telecommunication line and the power line. This clearance also provides some protection to the linemen.
+
+- The minimum clearance between the telecommunication line and the lighting fixture attached to the pole shall be 0.2 m.
+- The minimum clearance between telecommunication and low voltage power conductors at the mid-span shall be 0.3 m if the power conductor is insulated and 0.6 m otherwise.
+- The minimum clearances between power and telecommunication conductors at the joint-use pole, as a function of the power line nominal voltage, are shown in Table 1.
+
+The minimum clearances for the joint-use with low voltage lines are shown in Figure 2.
+
+**Table 1 – Minimum clearances between power and telecommunication conductors**
+
+| Phase-to-phase nominal voltage (kV) | Minimum clearance (m) |                |
+|-------------------------------------|-----------------------|----------------|
+|                                     | Insulated conductor   | Bare conductor |
+| $V \leq 1$                          | 0.5                   | 1.0            |
+| $1 < V \leq 15$                     | 1.0                   | 1.5            |
+| $15 < V \leq 25$                    | 1.5                   | 2.0            |
+
+![Diagram illustrating minimum clearances for joint-use of poles with low voltage power lines. It shows two poles. The left pole has a 'Bare low voltage conductor' and a telecommunication line. The right pole has an 'Insulated low voltage conductor' and a telecommunication line. The diagram indicates clearances: ≥ 1,0 m between the top of the pole and the power line; ≥ 0,5 m between the power line and the top of the telecommunication line; and ≥ 0,2 m between the bottom of the power line and the top of the telecommunication line. A horizontal line at the bottom is labeled 'Upper limit for telecommunication line'.](e9314c83043183351ed74908e9bf2f90_img.jpg)
+
+Diagram illustrating minimum clearances for joint-use of poles with low voltage power lines. It shows two poles. The left pole has a 'Bare low voltage conductor' and a telecommunication line. The right pole has an 'Insulated low voltage conductor' and a telecommunication line. The diagram indicates clearances: ≥ 1,0 m between the top of the pole and the power line; ≥ 0,5 m between the power line and the top of the telecommunication line; and ≥ 0,2 m between the bottom of the power line and the top of the telecommunication line. A horizontal line at the bottom is labeled 'Upper limit for telecommunication line'.
+
+**Figure 2 – Minimum clearances for joint-use of poles with low voltage power lines**
+
+## 9 Installation of surge protective devices
+
+The procedures contained in this Recommendation are intended to reduce the likelihood of a power-cross and to minimize its consequences if one occurs. However, in the joint-use of poles with power lines there is always a risk of the power current entering the cable core. Therefore, whenever the joint-use of poles with medium voltage power lines is used, it is necessary to install surge protective devices (SPDs) at the entrance of the subscriber premises and also at the telecommunications central office. The following procedures shall be observed:
+
+- The installation of SPDs at the customer premises shall comply with [\[ITU-T K.66\]](#).
+- The termination module for the SPD shall comply with [\[ITU-T K.65\]](#).
+- The SPD shall be equipped with protection against overheating ("fail safe") according to [\[IEC 61643-21\]](#).
+- Customer equipment shall comply with [\[ITU-T K.21\]](#).
+- Central office equipment shall comply with [\[ITU-T K.20\]](#).
+- Network equipment shall comply with [\[ITU-T K.45\]](#).
+
+NOTE – For the protection against power-cross it is especially important that the telecommunication equipment comply with the Mains Power Contact test contained in [\[ITU-T K.20\]](#), [\[ITU-T K.21\]](#) and [\[ITU-T K.45\]](#).
+
+It is worth mentioning that SPDs may be necessary at customer premises even if there is no joint-use of poles with medium voltage lines. For instance, SPDs may be necessary in lines exposed to the effects of lightning. For the assessment of the need for SPDs in these cases, the user shall refer to [[b-ITU-T K.46](#)] and [[b-ITU-T K.47](#)].
+
+## **10 Insulation coordination**
+
+The coordination of the insulation levels of the lines in joint-use of poles is necessary in order to reduce the risk of power-cross due to insulation failure of the power line. Appendix I provides the rationale for the insulation coordination recommended in this clause.
+
+The insulation coordination described in this clause applies to the joint-use of poles with power lines operating at voltages rated up to 25 kV (line-to-line). All insulation requirements refer to tests carried out under power frequency according to [IEC 60060-1]. The tests shall be carried out under artificial rain, with the test voltage applied for 10 seconds for withstand voltage assessment.
+
+### **10.1 Insulation of the telecommunication cable outer sheath**
+
+Telecommunication cables are usually covered with an outer plastic sheath that has an insulation level that is sufficiently high to provide adequate protection against power-crosses. This insulation level may be assessed by testing, observing the following:
+
+- The insulation under test is the one between the cable inner conductors (twisted pairs + metallic sheath, if any) and an outer electrode applied to the cable sample. This electrode shall not have sharp edges, in order to avoid local enhancement of the electric field.
+- The insulation withstand voltage shall be equal to or higher than 4 kV or twice the phase-to-earth voltage of the power line ( $V_E$ ) in joint use of poles, whichever is higher.
+
+### **10.2 Insulation of splices and distribution boxes**
+
+Splices and distribution boxes shall be insulated from the supporting strand and from the conductive poles. The insulation is between the inner metallic conductors (twisted pairs and metallic sheath) and the supporting strand or conductive pole. The insulation shall have the following characteristic:
+
+- The insulation withstand voltage shall be equal to or higher than 4 kV or twice the phase-to-earth voltage of the power line in joint-use of poles, whichever is higher.
+
+Preferably, splices and distribution boxes should inherently comply with this insulation requirement, so that no additional insulator or procedure would be required. Experience shows that conveniently designed splices and distribution boxes can comply with this requirement.
+
+### **10.3 Insulation between the metallic supporting strand and the pole**
+
+If the joint-use pole is conductive, an insulation shall be provided between the metallic supporting strand of the telecommunication line and the pole. Poles made of galvanized steel or steel-reinforced concrete are examples of conductive poles.
+
+If the joint-use pole is non-conductive, additional insulation is not required. Poles made of wood or composite materials (e.g., fibre-glass) are examples of non-conductive poles. If the pole is non-conductive, but it holds a bare vertical conductor of the power line (e.g., earthing conductor), then it shall be treated as a conductive pole.
+
+The insulation between the metallic supporting strand and the conductive pole shall have the following characteristics:
+
+- The insulation withstand voltage shall be equal to or higher than 4 kV or the phase-to-earth voltage of the power line in joint-use of poles, whichever is higher.
+
+- When in joint-use with a medium voltage power line, the strand insulation breakdown voltage shall be lower than the withstand voltage of the other components (cable, splices, and distribution boxes).
+
+The strand insulation may be provided by inserting an insulator between the strand and the pole. Ceramic insulators are commonly used for this purpose.
+
+The relations between the insulating characteristics of the telecommunication line components are summarized in Table 2. These relations are intended to achieve the insulation coordination for a telecommunication cable supported by a metallic strand in joint-use of conductive poles with a medium voltage power line. Parameter  $V_E$  in Table 2 is the phase-to-earth voltage of the power line. Figure 3 shows a simplified view of a line span, where the most relevant insulations are indicated.
+
+NOTE – If a serviceable telecommunication accessory is installed close to the supporting strand, then it is recommended to apply a low voltage insulating cover on the strand for an extension up to 1 m on each side of the accessory, in order to improve the safety of the service personnel.
+
+**Table 2 – Requirements for insulation coordination with a medium voltage line**
+
+| Insulation              | Withstand voltage            | Breakdown voltage                                          |
+|-------------------------|------------------------------|------------------------------------------------------------|
+| Cable outer sheath      | $\geq 2 V_E$ and $\geq 4$ kV | –                                                          |
+| Strand / pole           | $\geq V_E$ and $\geq 4$ kV   | Smaller than the withstand voltage of the other components |
+| Distribution box / pole | $\geq 2 V_E$ and $\geq 4$ kV | –                                                          |
+| Splice / strand or pole | $\geq 2 V_E$ and $\geq 4$ kV | –                                                          |
+
+![Figure 3: Simplified joint-use span with the most relevant insulations indicated. The diagram shows a medium voltage power distribution line supported by two conductive poles. A telecommunication cable is suspended between the poles, supported by a strand insulator. The cable is connected to an insulated splice, which is then connected to an insulated distribution box. The diagram indicates the insulation points: strand insulator, telecommunication cable, insulated splice, and insulated distribution box.](ddc7460821484f1ae2835c67955c554c_img.jpg)
+
+Figure 3: Simplified joint-use span with the most relevant insulations indicated. The diagram shows a medium voltage power distribution line supported by two conductive poles. A telecommunication cable is suspended between the poles, supported by a strand insulator. The cable is connected to an insulated splice, which is then connected to an insulated distribution box. The diagram indicates the insulation points: strand insulator, telecommunication cable, insulated splice, and insulated distribution box.
+
+**Figure 3 – Simplified joint-use span with the most relevant insulations indicated**
+
+## 11 Bonding and earthing
+
+### 11.1 Bonding
+
+The adjacent sections of the telecommunication cable metallic sheath shall be bonded together, in order to maintain its electrical continuity. This may require the installation of bonding conductors
+
+across the cable splices. The bonding conductor shall have a current carrying capacity equal to or higher than the capacity of the relevant cable sheath.
+
+The adjacent sections of the metallic supporting strand shall be bonded together, in order to maintain its electrical continuity. This may require the installation of bonding conductors across the poles where the strand is terminated. The bonding conductor shall have a current carrying capacity equal to or higher than the capacity of the strand.
+
+The telecommunication cable metallic sheath and the metallic supporting strand shall not be bonded together, in order to maintain the insulation coordination as per clause 10.
+
+### 11.2 Earthing
+
+The telecommunication cable metallic sheath and the metallic supporting strand shall have independent earthing connections.
+
+The telecommunication cable metallic sheath shall be connected to earth at least at the central office. Additional earthing connections along the line may be necessary in order to provide the desired protection against lightning (e.g., at the transition between underground and aerial installations). Refer to [\[b-ITU-T K.46\]](#) and [\[b-ITU-T K.47\]](#) for details about the lightning protection of telecommunication lines.
+
+The metallic supporting strand shall have earthing connections distributed along the line, so that any power-cross with a medium voltage power line will drain a current sufficiently high to trip the overcurrent protection of the power line. In order to do that, the following is required:
+
+- The resistance to earth at every point of the supporting strand shall be significantly lower than the fault resistance value considered by the power utility to set the tripping threshold of its protective equipment (e.g., circuit breaker), in case of a line-to-earth fault.
+
+It should be highlighted that the resistance to earth of the supporting strand ( $R_{eq}$ ) refers to the parallel association of all earthing resistances ( $R_g$ ) connected to the strand network, taking into account the series resistance ( $R_s$ ) of the strand itself, as shown in Figure 4. For instance, considering  $R_g = 30 \Omega$  and  $R_s = 5 \Omega$ , the resistance to earth of the supporting strand in Figure 3 has the following values:
+
+$$R_{eq} (1) = R_{eq} (5) = 14.2 \Omega,$$
+
+$$R_{eq} (2) = R_{eq} (4) = 13.6 \Omega, \text{ and}$$
+
+$$R_{eq} (3) = 12 \Omega.$$
+
+![Circuit diagram of a telecommunication supporting strand with five nodes (1-5), series resistors (Rs), and shunt earthing resistors (Rg) connected to ground at nodes 1, 3, and 5.](66c2bf11a8f117cddf67eff92d4c736c_img.jpg)
+
+The diagram shows a horizontal line representing the supporting strand with five nodes labeled 1, 2, 3, 4, and 5. Between each consecutive node (1-2, 2-3, 3-4, 4-5), there is a series resistor labeled  $R_s$ . At nodes 1, 3, and 5, there are shunt resistors labeled  $R_g$  connected vertically to a common ground symbol. Nodes 2 and 4 do not have shunt connections to ground.
+
+Circuit diagram of a telecommunication supporting strand with five nodes (1-5), series resistors (Rs), and shunt earthing resistors (Rg) connected to ground at nodes 1, 3, and 5.
+
+Figure 4 – Resistance to earth of the telecommunication supporting strand
+
+The maximum value of the resistance to earth provided by the telecommunication supporting strand shall be significantly lower than the value considered by the power utility in order to allow a safety margin due to the seasonal variations of earthing resistances and also due to the accidental loss of an earthing connection. This Recommendation suggests a safety factor of 0.5, which means that an upper
+
+limit value of  $20\ \Omega$  should be used for joint-use of poles with a power utility that considers  $40\ \Omega$  as the maximum earth fault impedance.
+
+The earthing connections of the telecommunication line shall be insulated from the joint-use conductive pole by means of an insulated down-conductor or by a bare down-conductor inserted inside a plastic conduit. In both cases, the insulation level shall comply with the cable insulation requirement, as per clause 10.1. This insulation shall be maintained at least up to 0.2 m at the aerial extremity and 2 m at the pole base, as shown in Figure 5.
+
+There shall be no earthing connection of the telecommunication line at poles that carry an earthing conductor of the power line (e.g., neutral earthing).
+
+![Diagram of an insulated down-conductor for telecommunication line earthing.](7efae06af3af43ffe5d4b956a679cf54_img.jpg)
+
+The diagram illustrates the earthing connection for a telecommunication line on a joint-use pole. A vertical yellow pole is shown. A horizontal line labeled 'Telecommunication cable' is connected to the pole. A down-conductor, labeled 'Insulated down-conductor', runs vertically along the pole. At the top, the down-conductor is connected to the telecommunication cable, and a dimension line indicates a distance of  $> 0.2\ \text{m}$  from the top of the pole. At the bottom, the down-conductor is connected to an 'Earthing electrode' (represented by a rod in the ground), and a dimension line indicates a distance of  $> 2\ \text{m}$  from the base of the pole. The ground level is indicated by a horizontal line with hatching below it.
+
+Diagram of an insulated down-conductor for telecommunication line earthing.
+
+**Figure 5 – Insulated down-conductor for telecommunication line earthing**
+
+## Appendix I
+
+### Rationale for the insulation coordination
+
+(This appendix does not form an integral part of this Recommendation.)
+
+The insulation coordination is intended to direct the overcurrent through a path away from the telecommunication cable core when there is an insulation failure in the power line. There are several reasons that can cause such overcurrent, such as a crack in the power line insulator, a tree branch falling across the insulator, flashover due to lightning, etc.
+
+Once there is a failure of the insulation between the power line conductor and a conductive pole, an overcurrent will flow to the ground through the pole foot. As a result, the pole potential will rise. If the insulation failure is due to mechanical reasons (e.g., crack of a ceramic insulator), the pole potential will be limited to the line-to-earth voltage of the power line. Therefore, if the insulation between the telecommunication strand and the pole can withstand this voltage, the current flow will not involve the telecommunication line.
+
+This situation is illustrated in Figure I.1, where a failure of the power conductor leads to a current flow through the pole, but the insulation between the telecommunication strand and the pole prevents the power current from reaching the telecommunication cable. For instance, if the power line is rated at 13.8 kV, then its line-to-earth voltage is 8.0 kV. If the insulator of the telecommunication strand can withstand 8.0 kV, then the power current will not flow through the telecommunication line and the insulation coordination is achieved.
+
+![Diagram illustrating insulation coordination resulting from a mechanical failure of the power line insulation. The diagram shows five poles supporting two lines: a top 'Power line conductor' and a bottom 'Telecom line strand'. Each pole is connected to ground via a 'Pole-foot earthing resistance'. The third pole from the left shows a mechanical failure of its power line insulator, indicated by a red lightning bolt symbol labeled 'Electric arc' between the power line and the pole. The other four poles have intact insulators. A legend box at the bottom identifies the symbols: a stack of three discs for 'Power line insulator', a blue hourglass shape for 'Telecom line insulator', a zigzag line for 'Pole-foot earthing resistance', and a red lightning bolt for 'Electric arc'.](41a438d7e4adc17c3a4005e7c9500091_img.jpg)
+
+Diagram illustrating insulation coordination resulting from a mechanical failure of the power line insulation. The diagram shows five poles supporting two lines: a top 'Power line conductor' and a bottom 'Telecom line strand'. Each pole is connected to ground via a 'Pole-foot earthing resistance'. The third pole from the left shows a mechanical failure of its power line insulator, indicated by a red lightning bolt symbol labeled 'Electric arc' between the power line and the pole. The other four poles have intact insulators. A legend box at the bottom identifies the symbols: a stack of three discs for 'Power line insulator', a blue hourglass shape for 'Telecom line insulator', a zigzag line for 'Pole-foot earthing resistance', and a red lightning bolt for 'Electric arc'.
+
+**Figure I.1 – Insulation coordination resulting from a mechanical failure of the power line insulation**
+
+Besides mechanical failure, the power line insulation may also breakdown due to overvoltages. The most common causes of such overvoltages are lightning flashes, either striking the line directly or striking nearby structures. In this case, the potential rise of the pole is not limited to the power line voltage, as part of the lightning surge may flow through the pole. Therefore, a flashover may occur
+
+across the telecommunication strand insulator. This effect is similar to the back-flashover of an overhead power transmission lines struck by lightning.
+
+However, as the strand is held by the same insulator in nearby poles, there will be flashovers from the strand to earth in these poles. As a result, the strand will act as an overhead earth wire and limit its potential with respect to earth at a value close to the breakdown voltage of its insulator. Therefore, if the withstand voltage of the cable conductors with respect to the strand and to the pole is higher than the breakdown voltage of the strand insulator, then no overcurrent will reach the cable core.
+
+This situation is shown in Figure I.2, where the power line insulation flashes over under a lightning induced voltage. The overcurrent reaches the strand due to the breakdown of the strand insulator at the central pole, and leaves the strand toward the earth due to the breakdown of the nearby strand insulators. For instance, if the breakdown voltage of the strand insulator is 15 kV and the withstand voltage of the cable outer sheath is 20 kV, then the insulation coordination is achieved.
+
+![Diagram illustrating insulation coordination resulting from a flashover of the power insulator due to an overvoltage.](8307f6b04df072c9332f9987e034272c_img.jpg)
+
+The diagram shows a horizontal power line conductor supported by five insulators. Below it, a telecommunication line strand is supported by five corresponding insulators. Each insulator assembly is connected to a pole-foot earthing resistance, represented by a zigzag line and a ground symbol. The central power line insulator has experienced a flashover, indicated by a jagged orange lightning bolt striking from the conductor to the strand. From the strand, five orange lightning bolts (electric arcs) strike down to the ground at each pole-foot earthing resistance. Horizontal orange arrows on the strand indicate current flow away from the central pole towards the adjacent poles. A legend box at the bottom identifies the symbols: a stack of three discs for 'Power line insulator', a blue hourglass shape for 'Telecom line insulator', a zigzag line for 'Pole-foot earthing resistance', and a jagged orange line for 'Electric arc'.
+
+Diagram illustrating insulation coordination resulting from a flashover of the power insulator due to an overvoltage.
+
+**Figure I.2 – Insulation coordination resulting from a flashover of the power insulator due to an overvoltage**
+
+## Bibliography
+
+- [b-ITU-T K.26] Recommendation ITU-T K.26 (2008), *Protection of telecommunication lines against harmful effects from electric power and electrified railway lines.*
+- [b-ITU-T K.46] Recommendation ITU-T K.46 (2012), *Protection of telecommunication lines using metallic symmetric conductors against lightning-induced surges.*
+- [b-ITU-T K.47] Recommendation ITU-T K.47 (2012), *Protection of telecommunication lines against direct lightning flashes.*
+- [b-IEC 60050] IEC 60050 (2010), *International Electrotechnical Vocabulary.*
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | General tariff principles                                                                                                                                 |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| Series G        | Transmission systems and media, digital systems and networks                                                                                              |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| <b>Series K</b> | <b>Protection against interference</b>                                                                                                                    |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| Series P        | Terminals and subjective and objective assessment methods                                                                                                 |
+| Series Q        | Switching and signalling                                                                                                                                  |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities                               |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |

marked/K/T-REC-K.109-201511-I_PDF-E/raw.md

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+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**K.109**
+
+(11/2015)
+
+SERIES K: PROTECTION AGAINST INTERFERENCE
+
+# --- **Installation of telecommunication equipment on utility poles**
+
+Recommendation ITU-T K.109
+
+ITU-T
+
+![ITU logo](84a1d09fb489061482111515543b60dc_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a globe with a red lightning bolt striking across it. To the right of the globe, the text "International Telecommunication Union" is written in blue, with "ITU" in a larger, bold font above it.
+
+ITU logo
+
+International  
+Telecommunication  
+Union
+
+
+
+# Recommendation ITU-T K.109
+
+# Installation of telecommunication equipment on utility poles
+
+## Summary
+
+Recommendation ITU-T K.109 provides guidelines for the installation of telecommunication equipment and/or antennas on utility poles. These guidelines cover the clearances from the power conductors, the requirements for insulation, earthing and bonding, and the protective procedures to avoid interference and damage from the electromagnetic fields generated by the nearby power conductors and lightning flashes. The power distribution lines considered are those operating in alternating or direct current, with nominal voltages up to 25 kV. These lines may be used for power distribution, street lighting, or electrified railways.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T K.109    | 2015-11-29 | 5           | <a href="http://handle.itu.int/11.1002/1000/12670">11.1002/1000/12670</a> |
+
+## Keywords
+
+Clearances, earthing, joint use of poles, power lines, telecommunication equipment, utility poles.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2016
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                    | Page |
+|----------------------------------------------------|------|
+| 1 Scope.....                                       | 1    |
+| 2 References.....                                  | 1    |
+| 3 Definitions .....                                | 1    |
+| 3.1 Terms defined elsewhere .....                  | 1    |
+| 3.2 Terms defined in this Recommendation.....      | 2    |
+| 4 Abbreviations and acronyms .....                 | 2    |
+| 5 Conventions .....                                | 2    |
+| 6 General considerations.....                      | 2    |
+| 7 Resistibility requirements .....                 | 2    |
+| 8 Minimum clearances.....                          | 2    |
+| 9 Installation of the equipment .....              | 3    |
+| 10 Earthing and bonding.....                       | 4    |
+| 11 Protection against electromagnetic fields ..... | 5    |
+| Bibliography.....                                  | 7    |
+
+
+
+## Recommendation ITU-T K.109
+
+# Installation of telecommunication equipment on utility poles
+
+## 1 Scope
+
+This Recommendation provides guidelines for the installation of telecommunication equipment and/or antennas on utility poles carrying power distribution lines. The power lines considered are those operating in alternating or direct current, with nominal voltages up to 25 kV. These lines may be used for power distribution, street lighting, or traction lines (electrified railways).
+
+For the procedures regarding the joint use of poles between telecommunication lines and power lines, especially the prevention of accidental contacts between these lines (power-cross), the user shall refer to [b-ITU-T K.108].
+
+For guidance on the installation of telecommunication equipment in towers of power transmission lines (above 25 kV), the user shall refer to [b-ITU-T K.57].
+
+Some equipment used for smart-grid applications may contain telecommunication interfaces used for supervision and control of the electric power grid, which may be installed close to or on the energized power conductors. This type of equipment is outside the scope of this Recommendation.
+
+## 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T K.45] Recommendation ITU-T K.45 (2015), *Resistibility of telecommunication equipment installed in the access and trunk networks to overvoltages and overcurrents*.
+- [ITU-T K.50] Recommendation ITU-T K.50 (2000), *Safe limits of operating voltages and currents for telecommunication systems powered over the network*.
+- [IEC 60060-1] IEC 60060-1 (2010), *High-voltage test techniques - Part 1: General definitions and test requirements*.
+
+## 3 Definitions
+
+### 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 low-voltage:** Voltage having a value below a conventionally adopted limit.
+
+NOTE – For the distribution of AC electric power, the upper limit is generally accepted to be 1000 V. (IEC IEV 151-15-03 of [b-IEC IEV])
+
+**3.1.2 residual current device (RCD):** A mechanical switching device designed to make, carry and break currents under normal service conditions and to cause the opening of the contacts when the residual current attains a given value under specified conditions. (IEC IEV 442-05-02 of [b-IEC IEV]).
+
+NOTE – A residual current device can be a combination of various separate elements designed to detect and evaluate the residual current and to make and break current.
+
+### **3.2 Terms defined in this Recommendation**
+
+None.
+
+## **4 Abbreviations and acronyms**
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|       |                                                    |
+|-------|----------------------------------------------------|
+| AC    | Alternating Current                                |
+| DC    | Direct Current                                     |
+| EBB   | Equipotential Bonding Bar                          |
+| ESD   | Electrostatic Discharge                            |
+| PEN   | Protective Earth and Neutral                       |
+| RCD   | Residual Current Device                            |
+| RF    | Radio-Frequency                                    |
+| SPD   | Surge Protective Device                            |
+| $V_N$ | Nominal phase-to-phase Voltage (of the power line) |
+
+## **5 Conventions**
+
+None.
+
+## **6 General considerations**
+
+Telecommunication operators that wish to install equipment on poles already used by power utilities are recommended, when national laws and regulations permit such an arrangement, to take the following general considerations into account:
+
+- the economic and aesthetic advantages to be derived from installing telecommunication equipment on utility poles;
+- the use of utility poles by telecommunication operators increases the likelihood of danger in comparison with that of an exclusive pole, both to staff and to the equipment. Special training of personnel working in such environments is highly desirable, especially when the nominal power line voltage is above 1 kV;
+- special formal agreements are desirable between the telecommunication operator and the power utility in the case of such installation, in order to define responsibilities.
+
+## **7 Resistibility requirements**
+
+Telecommunication equipment intended to be installed on utility poles shall comply with the resistibility requirements contained in [ITU-T K.45].
+
+## **8 Minimum clearances**
+
+In order to reduce the likelihood of accidents due to the proximity between the telecommunication equipment and the energized power conductors, a minimum clearance shall be maintained:
+
+- the minimum clearance between the telecommunication equipment (including its antenna) and the lighting fixture attached to the pole shall be 0.2 m;
+- the minimum clearance between the telecommunication equipment (including its antenna) and a power line conductor, as a function of its nominal voltage ( $V_N$ ) and insulation, is given in Table 1.
+
+**Table 1 – Minimum clearances between telecommunication equipment and power conductors**
+
+| Nominal voltage (kV) |                      | Minimum clearance (m) |                |
+|----------------------|----------------------|-----------------------|----------------|
+| AC                   | DC                   | Insulated conductor   | Bare conductor |
+| $V_N \leq 1^{(1)}$   | $V_N \leq 1.5^{(1)}$ | 0.5                   | 1.0            |
+| $1 < V_N \leq 15$    | $1.5 < V_N \leq 23$  | 1.0                   | 1.5            |
+| $15 < V_N \leq 25$   | $23 < V_N \leq 38$   | 1.5                   | 2.0            |
+
+<sup>(1)</sup> Low-voltage
+
+The minimum clearances for the installation of telecommunication equipment in low-voltage utility poles are shown in Figure 1. The upper limit shown in this figure shall be observed during the installation of the equipment, taking into account the height of its antenna.
+
+![Diagram illustrating minimum clearances for telecommunication equipment on low-voltage utility poles. It shows two pole configurations. The left pole has a 'Bare low-voltage conductor' at the top. The right pole has an 'Insulated low-voltage conductor' at the top. Both poles show the 'Upper limit for telecommunication equipment (including its antenna)'. Clearances are indicated: ≥ 1.0 m between the top conductor and the equipment limit on the left; ≥ 0.5 m between the top conductor and the equipment limit on the right; and ≥ 0.2 m between the equipment limit and a lower conductor on both poles. The diagram is labeled K.109(15)_F01.](b3baf3a29b67c7425d2562ddbc52f0cc_img.jpg)
+
+Diagram illustrating minimum clearances for telecommunication equipment on low-voltage utility poles. It shows two pole configurations. The left pole has a 'Bare low-voltage conductor' at the top. The right pole has an 'Insulated low-voltage conductor' at the top. Both poles show the 'Upper limit for telecommunication equipment (including its antenna)'. Clearances are indicated: ≥ 1.0 m between the top conductor and the equipment limit on the left; ≥ 0.5 m between the top conductor and the equipment limit on the right; and ≥ 0.2 m between the equipment limit and a lower conductor on both poles. The diagram is labeled K.109(15)\_F01.
+
+**Figure 1 – Minimum clearances for telecommunication equipment in low-voltage utility poles**
+
+## 9 Installation of the equipment
+
+The installation of telecommunication equipment on a utility pole depends on the type of pole considered. The utility poles can be classified as conductive or non-conductive. Conductive poles are those made of any metallic material (e.g., galvanized steel) or made of concrete with an internal steel reinforcement. Non-conductive poles are those made of wood, glass fibre, or any other composite material. Non-conductive poles carrying a bare earthing down-conductor of the power line shall be treated as a conductive pole.
+
+If the equipment is installed on the surface of a non-conductive pole, no special treatment is required. In this case, the equipment can be attached directly to the pole using regular fittings.
+
+If the telecommunication equipment is installed on the surface of a conductive pole, it may require additional protective procedures. This issue is currently under study.
+
+## 10 Earthing and bonding
+
+The earthing procedure applied to the telecommunication equipment may depend on the characteristics of the equipment enclosure. Any earthing procedure shall be agreed upon with the power utility and follow the applicable national rules.
+
+If the equipment enclosure is plastic or made of other non-conducting material, the equipment does not need to be connected to an earthing system. In this case, the service personnel shall be aware of the existence of any accessible live parts inside of the equipment.
+
+If the equipment enclosure is metallic, the following possibilities shall be considered:
+
+- if the telecommunication operator and the power utility agree, the equipment enclosure shall be bonded to the utility's protective earth conductor (if available). This situation is illustrated in Figure 2, where the protective earth and neutral (PEN) conductor is bonded to the equipment metallic enclosure through an equipotential bonding bar (EBB);
+- if the protective earth conductor is not available, the equipment shall be earthed by a dedicated down-conductor and an earthing electrode. In this case, the protection of the equipment against an internal short-circuit to the enclosure shall be provided by a residual current device (RCD), as shown in Figure 3;
+- if the equipment is remotely powered through the telecommunication line according to [ITU-T K.50] or if it is self-powered by means of a low-voltage source (e.g., photovoltaic cell), then it does not need to be earthed.
+
+![Diagram of equipment earthing by the PEN conductor.](b8661c6c54f72ecc7ff6cb05e47b2891_img.jpg)
+
+The diagram illustrates the earthing configuration within an equipment enclosure. A 'Power supply' unit and an 'Equipment circuit board' are shown. A 'Phase' conductor (blue line) enters from the bottom, passes through a 'Circuit breaker', and connects to the power supply. A 'PEN' conductor (green line) also enters from the bottom, connects to an 'Equipotential bonding bar' (green rectangle) inside the enclosure, and is connected to the equipment circuit board and the metallic 'Equipment enclosure'. The circuit breaker is connected to the PEN conductor via a blue component, likely a residual current device (RCD). The label 'K.109(15)\_F02' is present at the bottom right of the diagram.
+
+Diagram of equipment earthing by the PEN conductor.
+
+**Figure 2 – Equipment earthing by the PEN conductor**
+
+![Diagram of equipment earthing by a dedicated conductor. Inside an equipment enclosure, a power supply and an equipment circuit board are shown. Power conductors (blue lines) connect the power supply to an RCD (Residual Current Device). The RCD is connected to an earthing conductor (green line) which leads to an earth terminal. The earthing conductor is also connected to an equipotential bonding bar (green line) inside the enclosure. The equipment circuit board is connected to the equipotential bonding bar. The diagram is labeled K.109(15)_F03.](cfef993dcc8fb513de79eb1f93cf26ae_img.jpg)
+
+Diagram of equipment earthing by a dedicated conductor. Inside an equipment enclosure, a power supply and an equipment circuit board are shown. Power conductors (blue lines) connect the power supply to an RCD (Residual Current Device). The RCD is connected to an earthing conductor (green line) which leads to an earth terminal. The earthing conductor is also connected to an equipotential bonding bar (green line) inside the enclosure. The equipment circuit board is connected to the equipotential bonding bar. The diagram is labeled K.109(15)\_F03.
+
+**Figure 3 – Equipment earthing by a dedicated conductor**
+
+## 11 Protection against electromagnetic fields
+
+When telecommunication equipment is installed on a utility pole, it is exposed to the electromagnetic fields generated by the power conductors. Damage to the equipment can be caused by the electric field generated by a power conductor, which can be installed on the same pole or on a nearby line. Field experience shows that the power-frequency electric fields from a nearby power conductor can damage the input radio-frequency (RF) circuit of certain types of radio transceivers.
+
+This is usually the case of radio transceivers whose RF circuit is coupled to the antenna through a series capacitor. For the low-frequency inducing field, the stray capacitance between the power conductor and the antenna forms a capacitive voltage divider, resulting in a substantial voltage applied to the input capacitor. Depending on the capacitor characteristics, the voltage of the power conductor and the relative position between the antenna and the power conductor, the input capacitor may be damaged and put the transceiver out of service.
+
+Even if there is no power line nearby, this type of transceiver can be damaged due to lightning flashes. The coupling process is similar to the one described before, but in this case the inducing electric field is generated by the lightning flash. Details about this mechanism and some protective measures can be found in [b-Barbosa].
+
+In order to avoid this kind of damage, it is recommended that the radio transceiver used in utility poles has a shunt inductor between the RF circuit and the antenna. This inductor presents a short-circuit to the power-frequency and lightning electromagnetic fields, while presenting an open-circuit to the RF signal. There are several commercial transceivers that use this type of filter and this is a key aspect for providing reliable operation when attached to a utility pole. The shunt inductor also provides protection against electrostatic discharges (ESDs) and this is often the main reason for its installation. The RF circuits protected by shunt inductors are often referred as "DC earthed" or "DC grounded". Figure 4 shows a diagram with an RF circuit protected by a shunt inductor.
+
+![Circuit diagram showing an antenna connected to an RF circuit and a shunt inductor. The antenna is at the top, connected to a node. From this node, one path goes right to 'RF circuit', and the other path goes down through a 'Shunt inductor' to a ground symbol. The label 'K.109(15)_F04' is at the bottom right.](d4af765160d04ecef538e5066006dc77_img.jpg)
+
+Circuit diagram showing an antenna connected to an RF circuit and a shunt inductor. The antenna is at the top, connected to a node. From this node, one path goes right to 'RF circuit', and the other path goes down through a 'Shunt inductor' to a ground symbol. The label 'K.109(15)\_F04' is at the bottom right.
+
+**Figure 4 – RF circuit protected by a shunt inductor ("DC grounded")**
+
+The shunt inductor behaves as a high-pass filter, blocking the power-frequency energy as well as the energy from surges induced either by lightning flashes or by power line switching. The protective effect of this filter is described in detail in [b-ITU-T K.96], alongside with other types of filters. Figure 5, adapted from [b-ITU-T K.96], illustrates the action of the high-pass filter in protecting the frequency spectrum used by the RF signal from the potentially destructive energy coupled to the radio antenna by the power line and lightning flashes.
+
+![Graph showing Normalized amplitude (log scale from 0.0001 to 1) versus Frequency - Hz (log scale from 10 to 1 G). The graph illustrates the protective effect of a shunt inductor as a high-pass filter. The 'A.C. power service' and 'Surge spectrum' are shown as shaded areas that are attenuated by the 'High-pass filter' (indicated by a steep line). The 'RF spectrum' is shown as a shaded area that passes through the filter. The label 'K.109(15)_F05' is at the bottom right.](42ff8b598a0818ca8b6ef30850ad5f4e_img.jpg)
+
+Graph showing Normalized amplitude (log scale from 0.0001 to 1) versus Frequency - Hz (log scale from 10 to 1 G). The graph illustrates the protective effect of a shunt inductor as a high-pass filter. The 'A.C. power service' and 'Surge spectrum' are shown as shaded areas that are attenuated by the 'High-pass filter' (indicated by a steep line). The 'RF spectrum' is shown as a shaded area that passes through the filter. The label 'K.109(15)\_F05' is at the bottom right.
+
+**Figure 5 – Protective effect of the shunt inductor as a high-pass filter**
+
+## Bibliography
+
+- [b-ITU-T K.57] Recommendation ITU-T K.57 (2003), *Protection measures for radio base stations sited on power line towers*.
+- [b-ITU-T K.96] Recommendation ITU-T K.96 (2014), *Surge protective components: Overview of surge mitigation functions and technologies*.
+- [b-ITU-T K.108] Recommendation ITU-T K.108 (2015), *Joint use of poles by telecommunication and solidly earthed power lines*.
+- [b-Barbosa] C.F. Barbosa and F.E. Nallin (2015), *Lightning protection of a smart grid sensor*, Electric Power Systems Research, Vol. 118, Jan; pp. 83-88.
+- [b-IEC IEV] IEC 60050, *International Electrotechnical Vocabulary (IEV)*.
+
+
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | General tariff principles                                                                                                                                 |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| Series G        | Transmission systems and media, digital systems and networks                                                                                              |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| <b>Series K</b> | <b>Protection against interference</b>                                                                                                                    |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| Series P        | Terminals and subjective and objective assessment methods                                                                                                 |
+| Series Q        | Switching and signalling                                                                                                                                  |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities                               |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |

marked/K/T-REC-K.110-201512-I_PDF-E/raw.md

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+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**K.110**
+
+(12/2015)
+
+SERIES K: PROTECTION AGAINST INTERFERENCE
+
+---
+
+**Lightning protection of the dedicated  
+transformer for radio base station**
+
+Recommendation ITU-T K.110
+
+ITU-T
+
+![ITU logo](84a1d09fb489061482111515543b60dc_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a globe with a red lightning bolt striking it. To the right of the globe, the text "International Telecommunication Union" is written in blue, with "ITU" in a larger, bold font above it.
+
+ITU logo
+
+International  
+Telecommunication  
+Union
+
+
+
+# Recommendation ITU-T K.110
+
+# Lightning protection of the dedicated transformer for radio base station
+
+## Summary
+
+Recommendation ITU-T K.110 addresses lightning protection of the dedicated transformer for a radio base station (RBS).
+
+RBSs are usually powered by the local power utility with a dedicated power line operating at medium voltage (e.g., from 10 kV to 20 kV). A dedicated transformer is installed at the RBS for transforming the medium voltage (MV) to low voltage (LV) (e.g., 380 V or 240 V), which is then used to power the RBS.
+
+Frequently, the dedicated transformer is installed on a pole, and thus the associated overhead lines (medium and low voltage) have poor earthing conditions. Therefore, these transformers are exposed to lightning effects and, consequently, the power interruptions caused by lightning flashes can severely affect normal operations of the RBS.
+
+The main objective of this Recommendation is to reduce the risk of damage to an RBS dedicated transformer due to lightning flashes, which will improve the safety and reliability of the RBS itself and its related equipment.
+
+This Recommendation includes the following features:
+
+- 1) need of protection for dedicated transformer;
+- 2) earthing and bonding of transformer and RBS;
+- 3) direct lightning protection for transformers;
+- 4) transformer insulation requirements;
+- 5) MV/LV arresters and LV surge protective devices (SPDs);
+- 6) protection of ancillary facilities.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T K.110    | 2015-12-14 | 5           | <a href="http://handle.itu.int/11.1002/1000/12669">11.1002/1000/12669</a> |
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2016
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|      |                                                                   | Page |
+|------|-------------------------------------------------------------------|------|
+| 1    | Scope.....                                                        | 1    |
+| 2    | References.....                                                   | 1    |
+| 3    | Definitions .....                                                 | 2    |
+| 3.1  | Terms defined elsewhere .....                                     | 2    |
+| 3.2  | Terms defined in this Recommendation .....                        | 2    |
+| 4    | Abbreviations and acronyms .....                                  | 3    |
+| 5    | Conventions .....                                                 | 3    |
+| 6    | Need for protection .....                                         | 3    |
+| 7    | Earthing network for transformer and RBS .....                    | 5    |
+| 7.1  | Basic principles .....                                            | 5    |
+| 7.2  | Common earthing network .....                                     | 5    |
+| 7.3  | Separated earthing network .....                                  | 5    |
+| 8    | Direct lightning protection.....                                  | 6    |
+| 9    | Transformer insulation level.....                                 | 6    |
+| 10   | MV/LV arresters requirements .....                                | 6    |
+| 11   | MV/LV arresters installation .....                                | 7    |
+| 11.1 | Protection schemes .....                                          | 7    |
+| 11.2 | Bonding of the transformer .....                                  | 8    |
+| 12   | Protection of ancillary facilities.....                           | 10   |
+| 12.1 | Power meters .....                                                | 10   |
+| 12.2 | Power conductors .....                                            | 10   |
+|      | Annex A – Calculation for lightning risk factors.....             | 12   |
+| A.1  | Lightning risk analysis .....                                     | 12   |
+| A.2  | Calculation examples.....                                         | 13   |
+|      | Appendix I – Analysis on the reasons of lightning damage .....    | 15   |
+| I.1  | Analysis of the processes that may lead to damage .....           | 15   |
+| I.2  | Reasons for transformer damage .....                              | 16   |
+| I.3  | Forward transformation overvoltage (FTO).....                     | 17   |
+| I.4  | Inverse transformation overvoltage (ITO).....                     | 17   |
+|      | Appendix II – Selection and installation of MV/LV arresters ..... | 19   |
+| II.1 | Solidly earthed power distribution systems.....                   | 19   |
+| II.2 | Non-solidly earthed power distribution systems .....              | 19   |
+| II.3 | Installation of MV/LV arresters and drop-out fuse .....           | 19   |
+|      | Bibliography.....                                                 | 21   |
+
+
+
+# Recommendation ITU-T K.110
+
+## Lightning protection of the dedicated transformer for radio base station
+
+# 1 Scope
+
+This Recommendation addresses the lightning protection of dedicated transformers used to provide electrical power for radio base stations (RBSs). It contains procedures for earthing, bonding and direct lightning protection of the dedicated transformer, including protection methods for the associated power lines, requirements for surge arresters (medium voltage (MV) and low voltage (LV) arresters), and protection procedures for ancillary facilities.
+
+Transformers used for powering an RBS and other components (i.e., shared transformers) are not covered in this Recommendation. The lightning protection of these shared transformers is contained in [b-ITU-T K.111].
+
+# 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T K.56] Recommendation ITU-T K.56 (2010), *Protection of radio base stations against lightning discharges*.
+- [ITU-T K.97] Recommendation ITU-T K.97 (2014), *Lightning protection of distributed base stations*.
+- [ITU-T K.112] Recommendation ITU-T K.112 (2015), *Lightning protection, earthing and bonding: Practical procedures for radio base station sites*.
+- [IEC 60076-3] IEC 60076-3 (2013), *Power transformers – Part 3: Insulation levels, dielectric tests and external clearances in air*.
+- [IEC 60076-4] IEC 60076-4 (2002), *Power transformers – Part 4: Guide to the lightning impulse and switching impulse testing – Power transformers and reactors*.
+- [IEC 60099-4] IEC 60099-4 (2014), *Surge arresters – Part 4: Metal-oxide surge arresters without gaps for a.c. systems*.
+- [IEC 61643-11] IEC 61643-11 (2011), *Low-voltage surge protective devices – Part 11: Surge protective devices connected to low-voltage power systems – Requirements and test methods*.
+- [IEC 62305-1] IEC 62305-1 (2010), *Protection against lightning – Part 1: General principles*.
+- [IEC 62305-2] IEC 62305-2 (2010), *Protection against lightning – Part 2: Risk management*.
+- [IEC 62305-3] IEC 62305-3, (2010), *Protection against lightning – Part 3: Physical damage to structures and life hazard*.
+
+# 3 Definitions
+
+## 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 continuous operating voltage of an arrester ( $U_c$ )** [IEC 60099-4]: Designated permissible r.m.s. value of power-frequency voltage that may be applied continuously between the arrester terminals in accordance with  $U_r$ .
+
+**3.1.2 non-solidly earthed power distribution systems** [b-IEC 60050-601]: System generally refers to neutral point ungrounded via arc suppression coil or high-impedance to ground. When short-circuit fault occurs, the system can not constitute a current loop, the fault current is very small, also known as small current grounding system.
+
+**3.1.3 rated voltage of an arrester ( $U_r$ )** [IEC 60099-4]: Maximum permissible RMS. value of power-frequency voltage between its terminals at which is designed to operate correctly under temporary overvoltage conditions as established in operating duty tests.
+
+**3.1.4 residual voltage of an arrester ( $U_{res}$ )** [IEC 60099-4]: Peak value of voltage that appears between the terminals of an arrester during the passage of discharge current.
+
+**3.1.5 solidly earthed neutral system** [b-IEC 60050-601]: System whose neutral point(s) is (are) earthed directly.
+
+## 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following terms:
+
+**3.2.1 arrester disconnector:** Device for disconnecting an arrester from the system in the event of arrester failure, to prevent a persistent fault on the system and to give visible indication of the failed arrester.
+
+NOTE – Eliminate the fault current through the arrester during disconnection generally is not a function of the device.
+
+**3.2.2 dedicated transformer:** Power transformer used exclusively to provide electrical power to a radio base station.
+
+**3.2.3 drop-out fuse:** Fuse used in MV power line and distribution transformers for overload and short circuit protection.
+
+**3.2.4 earthing network:** The part of an earthing installation that is restricted to the earth electrodes and their interconnections.
+
+**3.2.5 heat-blast disconnector:** Device that uses the explosion of a component in order to disconnect a circuit and interrupt the current flow.
+
+**3.2.6 high current impulse of an arrester:** Peak value of discharge current having a 4/10 impulse shape which is used to test the stability of the arrester on direct lightning strokes.
+
+**3.2.7 lightning protection insulator:** An insulator body comprising an upper part and a lower part connected series. When subjected to a lightning overvoltage, the nonlinear resistance of the lower part decreases and the overvoltage is concentrated at the upper part, causing a flashover. After the lightning current is over, the nonlinear resistance of the lower part rapidly rises and limits the flow of power frequency current.
+
+**3.2.8 metal-oxide surge arrester without gaps:** Arrester having non-linear metal-oxide resistors connected in series and/or in parallel without any integrated series or parallel spark gaps.
+
+**3.2.9 nominal discharge current of an arrester ( $I_n$ ):** Peak value of lightning current impulse (8/20  $\mu$ s current impulse) which is used to classify an arrester.
+
+**3.2.10 non-linear metal-oxide resistor:** Part of the surge arrester which, by its non-linear voltage versus current characteristics, acts as a low resistance to overvoltage, thus limiting the voltage across the arrester terminals, and as a high resistance at normal power-frequency voltage.
+
+**3.2.11 series reactor:** Device that limits the lightning current flow through a drop-out fuse, in order to avoid its undesired operation.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+EPR Earth Potential Rise
+
+FTO Forward Transformation Overvoltage
+
+ITO Inverse Transformation Overvoltage
+
+LV Low Voltage
+
+MV Medium Voltage
+
+RBS Radio Base Station
+
+SPD Surge Protective Device
+
+# 5 Conventions
+
+None.
+
+# 6 Need for protection
+
+Power utilities usually protect distribution transformers against lightning induced surges, but not against direct lightning flashes. However, a dedicated power transformer used to provide electrical power to an RBS is installed in an environment that is very exposed to direct flashes. The main items that enhance this high exposure include the presence of a tall metallic tower for the RBS, a long overhead power distribution line (feeder) and the RBS placement on a hill. Therefore, the dedicated power transformers for RBS presents a number of aspects that need to be considered:
+
+- earth potential rise (EPR) when lightning strikes the tower;
+- induced overvoltages when lightning strikes the tower;
+- low voltage (LV) and medium voltage (MV) lines nearby the transformer (within 3 km) may be struck by lightning.
+
+This Recommendation considers two possible earthing configurations:
+
+- 1) The transformer and the RBS share the same earthing network. This configuration is shown in Figure 1 and should be adopted when the distance between the transformer and the RBS is shorter than 30 m. When the tower is struck by lightning, the EPR may cause flashover of the line insulation at the nearest pole, and the current flowing through the MV arresters would be very high and would damage the arresters. Moreover, other components of the power system could also be damaged.
+- 2) The transformer and the RBS have separated earthing network. This configuration is shown in Figure 2, where the distance between the transformer and the RBS is usually longer than 30 m. When the tower is struck by lightning, the EPR will be applied to the LV side of the transformer and may lead to the breakdown of its insulation. Moreover, if not conveniently specified, the lightning arresters may also be damaged.
+
+![Figure 1: Reference configuration for earthing network. This diagram shows a lightning tower connected to an earth network. A red line indicates the earthing path from the tower, through an RBS (Radio Base Station) and its SPD (Surge Protection Device), to a transformer. The transformer is connected to 0.4 kV and 10/20 kV lines, with an SA (Surge Arrestor) and Z_T (transformer impedance) shown. The earthing path continues from the transformer through another SPD to an MV (Medium Voltage) line insulator, and finally to the earth of the pole. A dimension line indicates a distance D < 30 m for a jointly earth network. The diagram is labeled K.110(15)_F01.](a5ee5c23b6dc52ec1d724b76d5a5f58f_img.jpg)
+
+Figure 1: Reference configuration for earthing network. This diagram shows a lightning tower connected to an earth network. A red line indicates the earthing path from the tower, through an RBS (Radio Base Station) and its SPD (Surge Protection Device), to a transformer. The transformer is connected to 0.4 kV and 10/20 kV lines, with an SA (Surge Arrestor) and Z\_T (transformer impedance) shown. The earthing path continues from the transformer through another SPD to an MV (Medium Voltage) line insulator, and finally to the earth of the pole. A dimension line indicates a distance D < 30 m for a jointly earth network. The diagram is labeled K.110(15)\_F01.
+
+**Figure 1 – Reference configuration for earthing network**
+
+![Figure 2: Reference configuration for separated earthing network. This diagram shows a lightning tower connected to an earth network. A red line indicates the earthing path from the tower, through an RBS (Radio Base Station) and its SPD (Surge Protection Device), to an LV (Low Voltage) line insulator, and finally to the earth of the pole. Another red line shows the earthing path from the transformer (connected to 0.4 kV and 10/20 kV lines) through an SPD, SA (Surge Arrestor), and Z_T (transformer impedance) to the earth of the transformer. A dimension line indicates a distance D > 30 m for a separated earth network. The diagram is labeled K.110(15)_F02.](cfda9df1319e04207eb28bcefd1dab7b_img.jpg)
+
+Figure 2: Reference configuration for separated earthing network. This diagram shows a lightning tower connected to an earth network. A red line indicates the earthing path from the tower, through an RBS (Radio Base Station) and its SPD (Surge Protection Device), to an LV (Low Voltage) line insulator, and finally to the earth of the pole. Another red line shows the earthing path from the transformer (connected to 0.4 kV and 10/20 kV lines) through an SPD, SA (Surge Arrestor), and Z\_T (transformer impedance) to the earth of the transformer. A dimension line indicates a distance D > 30 m for a separated earth network. The diagram is labeled K.110(15)\_F02.
+
+**Figure 2 – Reference configuration for separated earthing network**
+
+The annual total number of flashes ( $N$ ) to the RBS site is considered in order to determine the required protection level (Basic, Reinforced, or Special) for the RBS site, as shown in Table 1. Annex A presents the procedure for calculating the total number of flashes ( $N$ ), as a function of the RBS configuration (common or separated earthing network).
+
+**Table 1 – Determination of the protection level**
+
+| Total annual number of flashes | Protection level |
+|--------------------------------|------------------|
+| $N \leq 0.5$                   | Basic            |
+| $0.5 < N \leq 1$               | Reinforced       |
+| $N > 1$                        | Special          |
+
+# 7 Earthing network for transformer and RBS
+
+## 7.1 Basic principles
+
+A transformer's earthing network should consider the distance between the transformer and the RBS, the site surroundings, geological conditions, soil composition, topography and other factors. The perimeter of the terrain may determine the boundaries of the earthing network.
+
+The depth of earthing electrodes is generally not less than 0.5 m. In rocky hill or gravel soil (thin rocky) situations, the earthing electrode depth should be determined according to the specific circumstances.
+
+The length of vertical earthing rods of the grounding system can be determined by the soil resistivity and presence of rocky layers. The number of vertical earthing rods of the grounding system can be determined by earthing network size and soil resistivity. Vertical earthing rods should be installed at least at the four corners of the earthing network and bonded to it.
+
+More details on earthing networks can be found in [ITU-T K.112].
+
+## 7.2 Common earthing network
+
+When the transformer and the RBS earthing network are within a range of 30 m, they should share a common earthing network (see Figure 1). The common earthing network should have the shape of a ring conductor, which shall surround the building foundations. The distance between the external walls of the building and the earthing ring should not be less than 0.5 m. The transformer, the RBS and the tower shall be connected to the earthing ring, as well as to the building foundation and other underground facilities, as shown in Figure 3.
+
+![Diagram of a ring shape earthing network. It shows a 'Transformer earth grid' on the left connected by a 'Horizontal earth electrode' to a 'RBS earth grid' on the right. The 'RBS earth grid' is a rectangular loop surrounding a 'Building foundation'. Vertical earth electrodes are shown at the corners of the RBS grid. A label 'K.110(15)_F03' is at the bottom right.](18442e4e239480f0c3c95b547aa8fde2_img.jpg)
+
+The diagram illustrates a ring-shaped earthing network. On the left, a 'Transformer earth grid' is shown as a dashed line forming a triangle. A 'Horizontal earth electrode' connects this grid to a 'RBS earth grid' on the right. The 'RBS earth grid' is a dashed rectangular loop that surrounds a 'Building foundation', which is represented by a solid rectangle with four black squares at its corners. Vertical earth electrodes are indicated by dots at the corners of the RBS grid. The label 'K.110(15)\_F03' is located at the bottom right of the diagram.
+
+Diagram of a ring shape earthing network. It shows a 'Transformer earth grid' on the left connected by a 'Horizontal earth electrode' to a 'RBS earth grid' on the right. The 'RBS earth grid' is a rectangular loop surrounding a 'Building foundation'. Vertical earth electrodes are shown at the corners of the RBS grid. A label 'K.110(15)\_F03' is at the bottom right.
+
+**Figure 3 – Ring shape earthing network**
+
+## 7.3 Separated earthing network
+
+When the distance between the transformer and the RBS is greater than 30 m, they shall have separated earthing network. The RBS earthing network is similar to the one described in clause 6.2, excepting that the transformer is not earthed in earthing network. The transformer earthing network shall comply with the following two requirements:
+
+- 1) A ring electrode in the form of a triangle shall be installed around the transformer and connected to it. This ring shall be made of horizontal electrodes buried at a minimum depth of 0.5 m.
+- 2) Three radial horizontal electrodes shall be installed, extending from the ring electrode. These radial electrodes shall have from 15 m to 20 m and be buried at least at 0.5 m in the soil. The end of each radial electrode shall be connected to a vertical rod, as shown in Figure 4.
+
+![Diagram of a transformer earthing network. It shows a central point connected to a 'Transformer earth grid' (represented by a dashed triangle). From the vertices of the triangle, three dashed lines extend outwards, labeled 'Horizontal earth electrode 15-20 m'. Each of these lines ends at a solid black dot. From the center of the triangle, a vertical dashed line extends downwards to another solid black dot, labeled 'Vertical earth electrode'. The diagram is labeled K.110(15)_F04.](007b053fe94a8348f75128a584503fd0_img.jpg)
+
+Diagram of a transformer earthing network. It shows a central point connected to a 'Transformer earth grid' (represented by a dashed triangle). From the vertices of the triangle, three dashed lines extend outwards, labeled 'Horizontal earth electrode 15-20 m'. Each of these lines ends at a solid black dot. From the center of the triangle, a vertical dashed line extends downwards to another solid black dot, labeled 'Vertical earth electrode'. The diagram is labeled K.110(15)\_F04.
+
+**Figure 4 – Transformer earthing network**
+
+# 8 Direct lightning protection
+
+If the transformer is mounted close to the RBS tower, the tower will provide lightning protection as detailed in [IEC 62305-3]. If this is not the case, then appropriate protection measures shall be taken. A protection example would be to have a lightning protection system (lightning rod and down conductor) added to the pole that supports the transformer.
+
+# 9 Transformer insulation level
+
+The transformer insulation level shall comply with [IEC 60076-3] and [IEC 60076-4]. The most relevant data for the transformer insulation level is summarized in Table 2.
+
+**Table 2 – Transformer insulation level**
+
+| Winding voltage level<br>kV (RMS) | Rated frequency<br>withstand voltage<br>kV (RMS) | Rated impulse withstand voltage kV (Peak) |              |
+|-----------------------------------|--------------------------------------------------|-------------------------------------------|--------------|
+|                                   |                                                  | Full-wave                                 | Chopped wave |
+| 20                                | 55                                               | 125                                       | 140          |
+| 10                                | 35                                               | 75                                        | 85           |
+| 0.4 (<1.1 kV)                     | 5                                                | 10                                        | –            |
+
+NOTE – A dedicated transformer located in the suburbs, rural or mountainous areas may be exposed to high overvoltage levels and may require higher insulation levels. These higher levels should be negotiated between the telecommunication operator and the transformer manufacturer.
+
+# 10 MV/LV arresters requirements
+
+MV/LV arresters should be waterproofed for outdoor mounting and the overall characteristics should comply with [IEC 60099-4]. The nominal current rating ( $I_N$ ) of the arresters used for protecting the dedicated transformer should be selected while taking into account the field experience at a particular location. In general, a common earthing network configuration (see Figure 1) presents a higher stress
+
+to the MV arrester, whereas a separated earthing network (see Figure 2) presents a higher stress to the LV arrester.
+
+If field experience is not available, the data in Table 3 should be used to determine the minimum nominal current rating ( $I_N$ ) of the arresters used for protecting the dedicated transformer. The required protection level is determined according to clause 6.
+
+**Table 3 – Minimum nominal current rating ( $I_N$ ) of the arresters (8/20  $\mu$ s waveshape)**
+
+| Protection level | Common earthing network |             | Separated earthing network |             |
+|------------------|-------------------------|-------------|----------------------------|-------------|
+|                  | MV arrester             | LV arrester | MV arrester                | LV arrester |
+| Basic            | 10 kA                   | 5 kA        | 5 kA                       | 10 kA       |
+| Reinforced       | 20 kA                   | 10 kA       | 10 kA                      | 20 kA       |
+| Special          | under study             | 20 kA       | under study                | under study |
+
+# 11 MV/LV arresters installation
+
+Arresters should be used for the protection of the dedicated transformer MV and LV sides. In order to reduce the arrester residual voltage between phase and ground terminals caused by lightning impulses, the impedance of conductors between the arrester and the transformer should be as small as possible. To this aim, the arresters should preferably be fixed on the transformer enclosure directly. The arrester earthing terminal shall be connected to the transformer enclosure and then to the earthing system. This bonding procedure shall be applied to both MV and LV sides and it allows to achieve the lowest residual voltage (see Figure 5).
+
+## 11.1 Protection schemes
+
+For the Basic protection level, the power distribution box shall have a LV surge protective device (SPD) for the three-phase (3 PH) load of the RBS, indicated as SPD1 in Figure 5. Moreover, another LV SPD shall be installed nearby the transformer LV side, indicated as SPD2 in Figure 5. The protection level of SPD1 shall be selected according to the resistibility level of the RBS equipment, whereas the protection level of SPD2 shall be lower than the insulation level of the transformer LV side for a full-wave impulse (see Table 2).
+
+![Figure 5: Protection scheme for Basic protection level. The diagram shows a 3-PH LOAD connected to a 0.4 kV busbar. Two LV surge protective devices, SPD1 and SPD2, are connected between the busbar and ground (Earth of LOAD, impedance Z_L). A transformer is connected between the 0.4 kV busbar and a 10/20 kV busbar. An MV surge arrester (SA) is connected between the 10/20 kV busbar and ground (Earth of transformer, impedance Z_T). Lightning strikes are shown on the MV lines and the 0.4 kV busbar. A horizontal double-headed arrow labeled 'Basic protection' spans the area from the load to the transformer. The diagram is labeled K.110(15)_F05.](4636adff5682a064f0ae5f13a1d464a6_img.jpg)
+
+Figure 5: Protection scheme for Basic protection level. The diagram shows a 3-PH LOAD connected to a 0.4 kV busbar. Two LV surge protective devices, SPD1 and SPD2, are connected between the busbar and ground (Earth of LOAD, impedance Z\_L). A transformer is connected between the 0.4 kV busbar and a 10/20 kV busbar. An MV surge arrester (SA) is connected between the 10/20 kV busbar and ground (Earth of transformer, impedance Z\_T). Lightning strikes are shown on the MV lines and the 0.4 kV busbar. A horizontal double-headed arrow labeled 'Basic protection' spans the area from the load to the transformer. The diagram is labeled K.110(15)\_F05.
+
+**Figure 5 – Protection scheme for Basic protection level**
+
+When the protection level is Reinforced or Special, besides the protection procedures for Basic protection level, additional protection shall be applied to the MV line, as shown in Figure 6. This additional protection can be line surge arresters or lightning protection insulators.
+
+![Figure 6: Protection scheme for Reinforced or Special protection level. The diagram shows a 3-PH LOAD connected to an MV line through SPD1. The MV line is protected by SPD2 and SA. A transformer is connected between the MV line (10/20 kV) and the LV line (0.4 kV). The LV line is protected by SPD2. The MV line is also protected by an insulator and an earth of pole. The diagram is labeled with 'Enhanced protection' and 'K.110(15)_F06'.](b9ecbc3baefab13719e000faa6e0c7eb_img.jpg)
+
+The diagram illustrates a protection scheme for a reinforced or special protection level. It shows a 3-PH LOAD connected to an MV line through SPD1. The MV line is protected by SPD2 and SA. A transformer is connected between the MV line (10/20 kV) and the LV line (0.4 kV). The LV line is protected by SPD2. The MV line is also protected by an insulator and an earth of pole. The diagram is labeled with 'Enhanced protection' and 'K.110(15)\_F06'.
+
+Figure 6: Protection scheme for Reinforced or Special protection level. The diagram shows a 3-PH LOAD connected to an MV line through SPD1. The MV line is protected by SPD2 and SA. A transformer is connected between the MV line (10/20 kV) and the LV line (0.4 kV). The LV line is protected by SPD2. The MV line is also protected by an insulator and an earth of pole. The diagram is labeled with 'Enhanced protection' and 'K.110(15)\_F06'.
+
+Figure 6 – Protection scheme for Reinforced or Special protection level
+
+## 11.2 Bonding of the transformer
+
+If the arrester earthing conductor is long, the equivalent overvoltage  $U_{eq}$  applied to the transformer is given by:
+
+$$U_{eq} = U_r + U_{line}$$
+
+where  $U_r$  is the residual voltage of SPD and  $U_{line}$  is the voltage drop along earthing conductor (see Figure 7). As the inductive voltage drop  $U_{line}$  may reach high values, the transformer insulation may be damaged even if the arrester is properly specified.
+
+![Figure 7: Incorrect bonding of MV arresters. The diagram shows a transformer with MV and LV sides. The MV side is connected to three arresters. The LV side is connected to three lines (L1, L2, L3) and a neutral (N). The transformer shell is connected to ground through a resistor R. The diagram is labeled with 'Transformer shell', 'MV side', 'LV side', 'Ueq = Ur + Uline', 'Ur', 'Uline', and 'K.110(15)_F07'.](16c1175b5f05a4b55e6d396fc51b15b3_img.jpg)
+
+The diagram illustrates the incorrect bonding of MV arresters. It shows a transformer with MV and LV sides. The MV side is connected to three arresters. The LV side is connected to three lines (L1, L2, L3) and a neutral (N). The transformer shell is connected to ground through a resistor R. The diagram is labeled with 'Transformer shell', 'MV side', 'LV side',  $U_{eq} = U_r + U_{line}$ ,  $U_r$ ,  $U_{line}$ , and 'K.110(15)\_F07'.
+
+Figure 7: Incorrect bonding of MV arresters. The diagram shows a transformer with MV and LV sides. The MV side is connected to three arresters. The LV side is connected to three lines (L1, L2, L3) and a neutral (N). The transformer shell is connected to ground through a resistor R. The diagram is labeled with 'Transformer shell', 'MV side', 'LV side', 'Ueq = Ur + Uline', 'Ur', 'Uline', and 'K.110(15)\_F07'.
+
+Figure 7 – Incorrect bonding of MV arresters
+
+Transformers are generally installed at a significant height above the ground, leading to a relatively long earthing conductor and, consequently, a high inductive voltage drop. For example, considering
+
+that each meter of down-conductor has approximately  $1.6 \mu\text{H}$ , assuming that the surge current may reach  $10 \text{ kA}/\mu\text{s}$ , then each meter of down-conductor would add about  $16 \text{ kV}$  to the voltage applied to the transformer winding.
+
+If the arrester ground terminal is directly connected to the transformer enclosure, the value of the voltage applied to the transformer is given basically by the arrester residual voltage, as the inductive voltage drop on the bonding conductor is strongly reduced. This situation is shown in Figure 8.
+
+![Figure 8: Correct bonding procedure of MV arresters. This schematic diagram shows a transformer with its shell grounded through a resistor R. On the MV side, three arresters are connected between phases A, B, and C and the transformer shell. The residual voltage of these arresters is labeled U_r. The distance from the transformer shell to the arresters is labeled U_line. The equivalent voltage across the transformer windings is labeled U_eq. On the LV side, the transformer has three windings connected to a common neutral point O, with phases labeled L1, N, L2, and L3. The diagram is labeled K.110(15)_F08.](724c7777b608e53be38b12b6fb3c43bc_img.jpg)
+
+Figure 8: Correct bonding procedure of MV arresters. This schematic diagram shows a transformer with its shell grounded through a resistor R. On the MV side, three arresters are connected between phases A, B, and C and the transformer shell. The residual voltage of these arresters is labeled U\_r. The distance from the transformer shell to the arresters is labeled U\_line. The equivalent voltage across the transformer windings is labeled U\_eq. On the LV side, the transformer has three windings connected to a common neutral point O, with phases labeled L1, N, L2, and L3. The diagram is labeled K.110(15)\_F08.
+
+**Figure 8 – Correct bonding procedure of MV arresters**
+
+When the MV/LV arresters are installed close to the transformer, the residual voltage between phase and earth of the arrester can be further reduced, as illustrated in Figure 9. In this case, the transformer down-conductor shall be connected to the common bonding point of the arresters and transformer enclosure, as shown in Figure 9.
+
+![Figure 9: Earthing and bonding configuration. This diagram shows a transformer with its shell connected to a crossarm. MV arresters (MV SA) on the MV side and LV surge protection devices (LV SPD) on the LV side are connected to a common bonding point on the crossarm. A down-conductor connects this crossarm to an earth electrode E. The transformer windings are shown on both MV and LV sides, with a common neutral point O. The diagram is labeled K.110(15)_F09.](9b6b5924b48bf2fd5f347f88f06f45b3_img.jpg)
+
+Figure 9: Earthing and bonding configuration. This diagram shows a transformer with its shell connected to a crossarm. MV arresters (MV SA) on the MV side and LV surge protection devices (LV SPD) on the LV side are connected to a common bonding point on the crossarm. A down-conductor connects this crossarm to an earth electrode E. The transformer windings are shown on both MV and LV sides, with a common neutral point O. The diagram is labeled K.110(15)\_F09.
+
+**Figure 9 – Earthing and bonding configuration**
+
+# 12 Protection of ancillary facilities
+
+## 12.1 Power meters
+
+The power meter installed at the RBS shall be protected against lightning. In addition to the earthing procedures that may be required by the power, the earthing bar of the power meter station shall be bonded to the RBS's earthing network. The bonding conductor shall extend from the power meter station up to the closest point of the RBS earthing system and, when applicable, it shall be in contact with the soil.
+
+This conductor shall be treated as part of the RBS earthing system and shall have a minimum cross section equal to 50 mm<sup>2</sup>.
+
+SPDs shall be installed at the RBS side of the power meter station (i.e., downstream of the circuit breakers), and these SPDs shall comply with [IEC 61643-11].
+
+The continuous operating voltage (service voltage) of the SPDs shall be sufficiently high so that it will not operate under normal operation or fault conditions of the power line. [IEC 61643-11] provides guidelines for the selection of the SPD continuous operating voltage.
+
+Figure 10 shows a possible configuration for the protection of the power meter.
+
+![Diagram of power meter protection configuration showing a transformer, power meter, SPDs, and earthing system.](cb4cfa42ce34febde7bdb882f3fc3094_img.jpg)
+
+The diagram illustrates the electrical configuration for protecting a power meter at a Remote Base Station (RBS). At the top, a 'Transformer' is shown with its 'Low voltage side' terminals labeled L1, L2, L3, and N. Below the transformer, an 'LV SPD' (Surge Protection Device) is connected between the three phase lines (L1, L2, L3) and the neutral line (N). A red line labeled 'Power meter trunk' connects the transformer's low voltage side to a 'Power meter' unit. Next to the power meter is another 'SPD' unit. Both the power meter and its associated SPD are connected to a common earthing bar. This earthing bar is bonded to the RBS's earthing network, represented by a vertical conductor extending into the ground. The ground itself is labeled 'Transformer earth'. A horizontal line at the bottom represents the ground level. A label 'Neutral point earthing' points to the connection between the transformer's neutral point and the ground. A label 'LV power line' points to the conductors entering the power meter from the ground. The diagram is labeled 'K.110(15)\_F10' in the bottom right corner.
+
+Diagram of power meter protection configuration showing a transformer, power meter, SPDs, and earthing system.
+
+Figure 10 – Protection of power meter
+
+## 12.2 Power conductors
+
+Power conductors enter the RBS from the transformer LV side, and the following aspects shall be considered:
+
+- if the power line is shielded, its shield shall be bonded to the electric board earthing bar;
+
+- preferably, the power conductors shall exit the electric board inside metallic ducts or trays that shall be bonded to the board frame. The use of plastic duct to carry the power conductors may require the installation of another set of SPDs close to the alternating current (AC) powered equipment (e.g., the power supply).
+
+## Annex A
+
+### Calculation for lightning risk factors
+
+(This annex forms an integral part of this Recommendation.)
+
+### A.1 Lightning risk analysis
+
+The protection need shall be evaluated by the risk assessment of loss of services ( $R_2$ ) according to [IEC 62305-2]. When the risk is greater than the tolerable risk  $R_T$ , defined by the network operator, protection measures are necessary. The comparison between the risk and the tolerable risk allows determining the lightning protection level (LPL) that the protection measure at each equipment interface has to withstand to reduce the risk below the tolerable risk.
+
+The purpose of risk management is to determine the protection level of MV side and LV side of the dedicated transformer. For this particular application, a simplified approach for the evaluation of the protection need, based on [IEC 62305-2], is presented in this Recommendation.
+
+The risk sources include flash to the tower, flash to MV lines, and flash to LV lines. So the protection procedures can be clustered according to the RBS and transformer configurations and to the expected number of direct flashes.
+
+For common earthing network:
+
+$$N = N_D + N_M \quad (\text{A.1})$$
+
+and for separated earthing network:
+
+$$N = N_D + N_L + N_M \quad (\text{A.2})$$
+
+where  $N$  is the annual total number of flashes to the site, and  $N_D$ ,  $N_M$ , and  $N_L$  are the annual number of flashes to the tower, MV line, and LV line, respectively.
+
+According to [ITU-T K.97], the number of direct flashes to the tower ( $N_D$ ) can be calculated by:
+
+$$N_D = 9 \times \pi \times c \times h_t^2 \times N_g \quad (\text{A.3})$$
+
+where
+
+$c$  exposition factor (equal to 1 for flat ground and 2 for mountain top)
+
+$h_t$  tower height (km)
+
+$N_g$  ground flash density (flashes  $\times \text{km}^{-2} \times \text{year}^{-1}$ ).
+
+The number of direct flashes to the MV lines ( $N_M$ ) can be calculated by:
+
+$$N_M = 40 \times N_g \times L \times C_I \times C_E \times C_T \times 10^6 \quad (\text{A.4})$$
+
+where
+
+$L$  length of the MV lines (m). It is determined by the distance between the upstream protection node and the boundary of protection from tower. Where the length of a line section is unknown,  $L = 1000$  m is to be assumed
+
+$C_I$  the installation factor of the line (see [IEC 62305-2], Table A.2)
+
+$C_T = 0.2$  (see [IEC 62305-2], Table A.3)
+
+$C_E$  the environmental factor (see [IEC 62305-2], Table A.4).
+
+Similarly, the number of direct flashes to the LV lines ( $N_L$ ) can be calculated by:
+
+$$N_L = 40 \cdot N_g \cdot L \cdot C_I \cdot C_E \cdot C_T \times 10^{-6} \quad (\text{A.5})$$
+
+where
+
+$L$  the length of the LV lines (m). It is determined by the distance between the transformer and the boundary of protection from tower.
+
+The annual total number of flashes ( $N$ ) is considered in order to determine the required protection level (Basic, Reinforced, or Special) for the RBS site, as shown in Table A.1.
+
+**Table A.1 – Determination of the protection level**
+
+| Total annual number of flashes | Protection level |
+|--------------------------------|------------------|
+| $N \leq 0.5$                   | Basic            |
+| $0.5 < N \leq 1$               | Reinforced       |
+| $N > 1$                        | Special          |
+
+### A.2 Calculation examples
+
+1) Flashes to the tower ( $N_D$ )
+
+If  $N_g = 0.04 \times T_d^{1.25} = 2.1$  per km<sup>2</sup> and year for  $T_d = 24$  (thunderstorm days/year)
+
+$$N_D = 9 \times \pi \times 2 \times (0.04)^2 \times 2.1 \approx 0.2 \text{ flashes per year}$$
+
+or if  $N_g = 0.04 \times T_d^{1.25} = 12.6$  for  $T_d = 100$  (thunderstorm days/year)
+
+$$N_D = 9 \times \pi \times 2 \times (0.04)^2 \times 12.6 \approx 1.2 \text{ flashes per year}$$
+
+2) Flashes to the MV line ( $N_M$ )
+
+$C_I = 1$  for aerial line
+
+$C_E = 1$  for line environmental is rural
+
+$C_T = 0.2$  (see [IEC 62305-2], Table A.3)
+
+$L = 500$  m (MV line is 500 m long)
+
+If  $N_g = 0.04 \times T_d^{1.25} = 2.1$  for  $T_d = 24$
+
+$$N_M = 40 \cdot N_g \cdot L \cdot C_I \cdot C_E \cdot C_T \times 10^{-6} = 40 \cdot 2.1 \cdot 500 \cdot 1 \cdot 1 \cdot 0.2 \cdot 10^{-6} = 0.0084 \text{ flashes per year}$$
+
+or if  $N_g = 0.04 \times T_d^{1.25} = 12.6$  for  $T_d = 100$
+
+$L = 3000$  m (MV line is 3000 m long)
+
+$$N_M = 40 \cdot N_g \cdot L \cdot C_I \cdot C_E \cdot C_T \times 10^{-6} = 40 \cdot 12.6 \cdot 3000 \cdot 1 \cdot 1 \cdot 0.2 \cdot 10^{-6} = 0.3 \text{ flashes per year}$$
+
+3) Flashes to the LV line ( $N_L$ )
+
+$C_I = 1$  for aerial line
+
+$C_E = 1$  for line environmental is rural
+
+$C_T = 1$  (see [IEC 62305-2], Table A.3)
+
+$L = 30$  metres for low voltage line is 30 metres long
+
+If  $N_g = 0.04 \times T_d^{1.25} = 2.1$  for  $T_d = 24$
+
+$$N_L = 40 \cdot N_g \cdot L \cdot C_I \cdot C_E \cdot C_T \times 10^{-6} = 40 \cdot 2.1 \cdot 30 \cdot 1 \cdot 1 \cdot 1 \cdot 10^{-6} = 0.0025 \text{ flashes per year}$$
+
+or if  $N_g = 0.04 \times T_d^{1.25} = 12.6$  for  $T_d = 100$
+
+$L = 500$  m (LV line is 500 m)
+
+$$N_L = 40 \cdot N_g \cdot L \cdot C_I \cdot C_E \cdot C_T \times 10^{-6} = 40 \cdot 12.6 \cdot 500 \cdot 1 \cdot 1 \cdot 1 \cdot 10^{-6} = 0.25 \text{ flashes per year}$$
+
+The results of these examples are summarized in Table A.2, along with the determination of the protection level required for the RBS and dedicated transformer.
+
+**Table A.2 – Examples of protection level determination**
+
+| <b>Conditions considered</b>                        | <b>Calculation of N</b>                      | <b>Protection level</b> |
+|-----------------------------------------------------|----------------------------------------------|-------------------------|
+| $T_d = 24$ and common earthing network              | $N = 0.2 + 0.0084 = 0.20084$<br>$N \leq 0.5$ | Basic                   |
+| $T_d = 60$ and common or separated earthing network | $N = 0.64 + 0.3 = 0.94$<br>$0.5 < N \leq 1$  | Reinforced              |
+| $T_d = 100$ and separated earthing network:         | $N = 1.2 + 0.25 + 0.3 = 1.75$<br>$N > 1$     | Special                 |
+
+# Appendix I
+
+## Analysis on the reasons of lightning damage
+
+(This appendix does not form integral part of this Recommendation.)
+
+### I.1 Analysis of the processes that may lead to damage
+
+For the MV and LV power distribution system (under 35 kV), the power utility only considers the protection of the conducted and induced overvoltage derived from a distant lightning flash, but not the direct lightning flash on, or near, the power lines and its effects on the transformer. Under this approach, only the MV side of the transformer are usually equipped with arresters. Considering the flashover of the lines to earth (the insulation level of MV lines is low) and the wave impedance of the MV lines, the discharge current capacity of the equipped MV arrester is low. For instance, in China the rated discharge current of MV arrester is only 5 kA (8/20  $\mu$ s waveshape). But due to the presence of a tall metallic tower of a RBS and the severe environment, the protection of dedicated transformers for RBSs becomes much more complex. The main processes that may lead to damage are described as follows.
+
+#### I.1.1 Influence from the EPR when lightning strikes a tower
+
+When lightning strikes a tall metallic tower, the lightning current flows into the earth and the EPR can reach a level of hundreds of kV or more. The operation of SPDs in RBS or MV arresters would deliver the high potential to the connected lines and the high potential would be transmitted along the lines. Two distinct situations need to be considered:
+
+- when the transformer and the RBS share the same earthing network, the conducted high voltage may cause the flashover of lines to earth on the nearest pole, and the current flowing through MV arresters would be very high, leading to damage of the MV arresters. Moreover, the safety of the power supply and the power lines are also affected;
+- when the transformer and the RBS have a separated earthing network, the EPR will be applied to the LV side of the transformer and may lead to the breakdown of its insulation.
+
+#### I.1.2 Induced voltages due to a lightning stroke current
+
+Due to the short distance between the transformer lines and the metallic tower, when the latter is struck by lightning, the induced voltages will be very high. Figure I.1 shows the diagram of the induced voltage when a lightning flash hits a tower.
+
+Because of the existence of a tall tower, the probability of a lightning flash stroke increases greatly, which can shorten the life of arresters and other protective devices. Therefore, these protective components shall be specified with a reasonable safety margin.
+
+![Diagram illustrating common-mode induced voltage due to a lightning strike to a tower. A lightning stroke from a thunder cloud strikes a tower. The tower is connected to a sharing earth grid. The tower is surrounded by a magnetic field. To the left of the tower is an RBS (Radio Base Station) and a transformer. The transformer is connected to two loops, each containing induced electric charge. The diagram is labeled K.110(15)_FI.1.](e69b9188aa2c14ec6b21c83f711fef65_img.jpg)
+
+Diagram illustrating common-mode induced voltage due to a lightning strike to a tower. A lightning stroke from a thunder cloud strikes a tower. The tower is connected to a sharing earth grid. The tower is surrounded by a magnetic field. To the left of the tower is an RBS (Radio Base Station) and a transformer. The transformer is connected to two loops, each containing induced electric charge. The diagram is labeled K.110(15)\_FI.1.
+
+**Figure I.1 – Common-mode induced voltage due to a lightning strike to a tower**
+
+#### I.1.3 Direct flashes to the lines
+
+Depending on the degree of exposure, the LV and MV aerial lines nearby the transformer (within 1~2 km) may be struck by a lightning flash. Due to the close distance between the point of stroke and the transformer, the MV arrester would operate first and thus the breakdown of the line insulation is unlikely. The overvoltage and overcurrent along the conductor will be very large, which may be beyond the capability of the MV arrester. Therefore, a dedicated transformer for the RBS needs a specific approach from a lightning protection point of view.
+
+### I.2 Reasons for transformer damage
+
+The main reasons for transformer damage include the following:
+
+- 1) When damaged MV arresters are not replaced in time, then the next lightning flash may destroy the transformer.
+- 2) Overvoltage from LV lines may breakdown the insulation of transformers directly.
+- 3) The earthing conductor of the arrester is too long so that the residual voltage drop on the arrester and earthing conductor would be higher than the insulation capacity of transformers. Figure I.2 shows an analysis of the residual voltage for an incorrect connection of transformer and arrester.
+
+![Diagram illustrating the incorrect connection of transformer and arrester. A lightning stroke strikes a line at point 'a'. The arrester is connected between the line and ground at point 'b'. The transformer is connected between the line and ground at point 'a'. The diagram shows the residual voltage drop U3 across the arrester and earthing conductor, which is the sum of the voltage drop U1 across the arrester and the voltage drop U2 across the earthing conductor. The diagram is labeled K.110(15)_FI.2.](90ddf538ef276510e2b631f7b96654e6_img.jpg)
+
+Diagram illustrating the incorrect connection of transformer and arrester. A lightning stroke strikes a line at point 'a'. The arrester is connected between the line and ground at point 'b'. The transformer is connected between the line and ground at point 'a'. The diagram shows the residual voltage drop U3 across the arrester and earthing conductor, which is the sum of the voltage drop U1 across the arrester and the voltage drop U2 across the earthing conductor. The diagram is labeled K.110(15)\_FI.2.
+
+**Figure I.2 – Incorrect connection of transformer and arrester**
+
+### I.3 Forward transformation overvoltage (FTO)
+
+The overvoltage from LV lines introduces a surge in LV winding, which produces a high voltage on the neutral point of MV side according to the ratio of the number of windings between MV and LV. If the MV neutral point is ungrounded and the MV winding is protected by surge arresters, a high voltage will appear on the MV neutral point, which may breakdown the MV neutral insulation and destroy the transformer. Figure I.3 illustrates this process.
+
+![Figure I.3 – Illustration of FTO](d734a6ea1b381280f043fcf70391b6db_img.jpg)
+
+The diagram shows a three-phase transformer with a primary (MV) winding labeled U1 and a secondary (LV) winding labeled U2. The MV side has three phases labeled A, B, and C, each with a surge arrester connected to ground. The MV neutral point is connected to ground through a gap. The LV side has three phases labeled a, b, and c, each with a surge arrester connected to ground. The LV neutral point is connected directly to ground. Arrows indicate the flow of overvoltage from the LV side through the transformer windings to the MV neutral point. The diagram is labeled K.110(15)\_FI.3.
+
+Figure I.3 – Illustration of FTO
+
+Figure I.3 – Illustration of FTO
+
+### I.4 Inverse transformation overvoltage (ITO)
+
+When the MV arresters operate, the lightning current flows into the earth grid and the potential would rise. Because the neutral point of LV side is connected to earth directly, the EPR is applied to the neutral of the LV windings. Then this high voltage will be applied on LV the winding mostly, because the surge impedance of winding is much higher than the one of the lines. Similar to the FTO, this overvoltage may destroy the insulation of neutral point or winding of MV side. Figure I.4 illustrates this process.
+
+![Figure I.4 – Illustration of ITO](ab846b81e78dbc8da2a6f9511e2f248a_img.jpg)
+
+The diagram shows a three-phase transformer with a primary (MV) winding labeled U1 and a secondary (LV) winding labeled U2. The MV side has three phases labeled A, B, and C, each with a surge arrester connected to ground. The MV neutral point is connected to ground through a gap. The LV side has three phases labeled a, b, and c, each with a surge arrester connected to ground. The LV neutral point is connected directly to ground. Arrows indicate the flow of overvoltage from the MV side through the transformer windings to the LV neutral point. The diagram is labeled K.110(15)\_FI.4.
+
+Figure I.4 – Illustration of ITO
+
+Figure I.4 – Illustration of ITO
+
+Theoretical and experimental investigation have shown that when lightning strikes a tower, surge voltage will be generated on the transformer MV side and LV side.
+
+Based on field experience and simulation results, when there is a lighting event on the tower of a base station or near the facility, the dedicated transformer of the based station will experience very high overvoltages on its low-voltage side terminals even for low peak values of lightning current. In most cases, these overvoltages are above the insulation level of the transformer, which will cause its failure. The installation of an SPD at the low-voltage side of the transformer will reduce the observed overvoltages to values far lower than the insulation level of the transformer and thus retain the reliability of the site.
+
+# Appendix II
+
+## Selection and installation of MV/LV arresters
+
+(This appendix does not form integral part of this Recommendation.)
+
+### II.1 Solidly earthed power distribution systems
+
+Metal-oxide surge arresters without gaps are widely used for solidly earthed power distribution systems. The rated voltage ( $U_R$ ) of the surge arrester should be greater than the maximum line-voltage that may occur on the power system. Continuous operating voltage ( $U_c$ ) should be greater than the maximum phase-voltage that maybe occur on the power system. Nominal discharge current ( $I_N$ ) should be greater than or equal to 10 kA, with residual voltage ( $U_{res}$ ) not greater than 65% and 52% of the nominal system insulation level of the MV and LV sides, respectively.
+
+Peak current value ( $I_{peak}$ , 4/10  $\mu\text{s}$ ) is selected by the manufacturer to obtain a particular discharge energy. The energy shall not be higher than the total energy in two line discharges of the classifying class or the energy due to one high current impulse, 100 kA, 4/10  $\mu\text{s}$ . If not applicable, operating duty tests shall be repeated with increased energy to cover the claimed energy.
+
+Heat-melt disconnectors may present a blind zone for the dedicated transformers. If the sample varistor breaks down momentary, it may form a carbonized channel, and the heat-melt disconnector will lose its heat source. In some cases (such as in as outdoor applications), the heat-melt disconnector may fail to operate. As the low-voltage side of the dedicated transformer has no overcurrent protection, lightning damage will cause permanent system failure.
+
+Heat-blast disconnectors shall have low residual voltage, in order to have little effect on the residual voltage accumulated on the arrester. Mounting-bracket materials for disconnectors and arresters should use waterproof materials. The use of plastic materials should be avoided, as its service life is much shorter than that of composite materials.
+
+### II.2 Non-solidly earthed power distribution systems
+
+For non-solidly earthed power distribution systems, the power supply does not switch off when one phase short circuits to ground, and the other two phases raise up to the line voltage. As the dedicated transformer is usually connected to a long power line that has a relatively low load, these conditions may give rise to intermittent arcing discharge or ferromagnetic resonance overvoltage. The overvoltage amplitude may exceed the arrester  $U_R$ . Once resonance overvoltage happens, they will be sustained until the line resonance conditions remain. This duration may be much greater than the tolerance time of  $U_R$  (e.g., it may be much much longer than 10 s).
+
+This kind of overvoltage does not threaten the other power supply equipment, other than metal-oxide surge arresters without gaps. These devices may explode when installed in non-solidly earthed power distribution systems, when the resonant voltage amplitude and duration exceed the arrester capabilities. Therefore, the specification of the arrester rated voltage and protective level (residual voltage) requires a compromising solution.
+
+For non-solidly earthed power distribution systems, the power-frequency withstand voltage should be greater than or equal to  $1.4 U_R$  ( $1.4 \times 17 = 24$  kV). However, the residual voltage of the arrester is likely to exceed the transformer insulation, which will compromise the insulation coordination. In this case, metal-oxide surge arresters without gaps are recommended.
+
+### II.3 Installation of MV/LV arresters and drop-out fuse
+
+For maintenance purposes and also to improve the arrester performance, MV arresters are usually mounted on the rear side of a drop-out fuse. In this case, the lightning current goes through the drop-out fuse first, and then flows into the ground via arresters. As transformers have small-size fuses, when a large lightning current passes through the arrester, the fuse will still operate.
+
+During a thunderstorm, a first lightning stroke may operate the drop-out fuse. When a second lightning pulse arrives, it may cause flashover of the support insulator flashover. Moreover, due to the single-phase loss, the other phases will be overloaded and the system may switch off. On the other hand, if the arrester is installed in front of a drop-out fuse, the maintenance becomes difficult.
+
+Because most of the lightning surges come from the MV side of the transformer, additional protection should be installed before the drop-out fuse. By doing this, part of the energy of the incoming lightning surge is prevented from reaching the transformer, avoiding the problems caused by drop-out fuse operation. This additional protection can be arresters or specially-designed lightning insulators, installed on a pole located about 2 to 3 line spans from the transformer. In thunderstorm-prone areas, additional protection should be installed at several points along the entire power line, in order to assure a high reliability. If the LV line connected to a transformer is too long, the installation of additional protection on the LV line should be considered.
+
+# Bibliography
+
+- [b-ITU-T K.27] Recommendation ITU-T K.27 (2015), *Bonding configurations and earthing inside a telecommunication building.*
+- [b-ITU-T K.111] Recommendation ITU-T K.111 (2015), *Protection of surrounding structures of telecommunication towers against lightning.*
+- [b-IEC 60050-601] IEC 60050-601 (1985), *International Electrotechnical Vocabulary. Chapter 601: Generation, transmission and distribution of electricity – General.*
+
+
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | General tariff principles                                                                                                                                 |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| Series G        | Transmission systems and media, digital systems and networks                                                                                              |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| <b>Series K</b> | <b>Protection against interference</b>                                                                                                                    |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| Series P        | Terminals and subjective and objective assessment methods                                                                                                 |
+| Series Q        | Switching and signalling                                                                                                                                  |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects and next-generation networks                                                                 |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |

marked/K/T-REC-K.111-201511-I_PDF-E/raw.md

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+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**K.111**
+
+(11/2015)
+
+SERIES K: PROTECTION AGAINST INTERFERENCE
+
+# --- **Protection of surrounding structures of telecommunication towers against lightning**
+
+Recommendation ITU-T K.111
+
+ITU-T
+
+![ITU logo](84a1d09fb489061482111515543b60dc_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) features a globe with a red lightning bolt striking it. To the right of the globe, the text "International Telecommunication Union" is written in blue, with "ITU" in a larger, bold font above it.
+
+ITU logo
+
+International  
+Telecommunication  
+Union
+
+
+
+## Recommendation ITU-T K.111
+
+# Protection of surrounding structures of telecommunication towers against lightning
+
+## Summary
+
+Recommendation ITU-T K.111 considers the protection of structures in the area surrounding telecommunication towers (including masts and poles) against damage and injury derived from direct lightning flashes to the towers. The assessment and protection measures intend to reduce the possible risk derived from the erection of towers, but not to improve the overall lightning protection for every surrounding structure.
+
+This Recommendation considers towers whose height is less than 100 m from ground level, which rarely meets the initiation condition of upward flashes, so that the presence of the tower does not significantly influence the incidence of lightning flashes.
+
+Based on the analyses of sources of damage for an individual surrounding structure referring to IEC 62305-2, the risk components mostly include the possible influence in the close vicinity of a tower due to earth potential rise (EPR) and the transferred transients through common power feeds. For the former risk component, the hazard resulting from the occurrence of sparking and the injury to living beings are under consideration. For the latter, a series of exemption criteria and the corresponding protection (mitigation) measures are recommended. The requirements detailing the implementation of protection measures are also introduced.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T K.111    | 2015-11-29 | 5           | <a href="http://handle.itu.int/11.1002/1000/12668">11.1002/1000/12668</a> |
+
+## Keywords
+
+Earth potential rise, lightning protection, surrounding structures, telecommunication tower, transferred surge.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2016
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+###### Page
+
+|     |                                                                                                              |    |
+|-----|--------------------------------------------------------------------------------------------------------------|----|
+| 1   | Scope.....                                                                                                   | 1  |
+| 2   | References.....                                                                                              | 1  |
+| 3   | Definitions .....                                                                                            | 2  |
+| 3.1 | Terms defined elsewhere .....                                                                                | 2  |
+| 3.2 | Terms defined in this Recommendation.....                                                                    | 2  |
+| 4   | Abbreviations and acronyms .....                                                                             | 2  |
+| 5   | Conventions .....                                                                                            | 3  |
+| 6   | Reference configuration.....                                                                                 | 3  |
+| 7   | Protection of tower vicinity .....                                                                           | 3  |
+| 7.1 | Need of protection .....                                                                                     | 3  |
+| 7.2 | The assessment of the safety distance .....                                                                  | 5  |
+| 7.3 | Protection measures.....                                                                                     | 6  |
+| 7.4 | Protection measures against injury to living beings due to touch and step voltages.....                      | 8  |
+| 8   | Protection of local community with common power feed.....                                                    | 8  |
+| 8.1 | Need of protection .....                                                                                     | 8  |
+| 8.2 | Protection measures.....                                                                                     | 9  |
+| 9   | Implementation of protection measures.....                                                                   | 10 |
+|     | Annex A – Influence on the lightning risk of the surrounding structures due to the presence of a tower ..... | 11 |
+| A.1 | Possible lightning risk components derived from erection of a tower .....                                    | 11 |
+| A.2 | Risk from EPR on the close vicinity of a tower .....                                                         | 12 |
+| A.3 | Risk from transferred surge through common power feed.....                                                   | 13 |
+|     | Annex B – Determination of parameters for the assessment of safety distance .....                            | 16 |
+| B.1 | Lightning parameters according to LPL.....                                                                   | 16 |
+| B.2 | Reference values of Esoil .....                                                                              | 16 |
+| B.3 | Reference values of typical earthing impedance .....                                                         | 17 |
+| B.4 | Reference values of tower inductance .....                                                                   | 17 |
+|     | Appendix I – Influence of the tower on the ground flash density.....                                         | 18 |
+| I.1 | Downward flash.....                                                                                          | 18 |
+| I.2 | Upward flash .....                                                                                           | 18 |
+|     | Bibliography.....                                                                                            | 20 |
+
+
+
+## Recommendation ITU-T K.111
+
+# Protection of surrounding structures of telecommunication towers against lightning
+
+## 1 Scope
+
+This Recommendation considers the protection of structures in the neighbourhood of telecommunication towers (including masts and poles) against damage and injury derived from direct lightning flashes to the towers. These protection measures intend to reduce the possible risk derived from the erection of towers, but not to improve the overall lightning protection for every surrounding structure. The systemic protection for these structures should refer to the IEC 62305-x series.
+
+This Recommendation only considers towers whose heights are less than 100 m from ground level. Towers higher than 100 m or those situated on mountain ridges or high hills are not considered in this Recommendation.
+
+The lightning protection of telecommunication sites attached to the tower, such as a radio base station (RBS) and a dedicated telecommunication building, is not included in this Recommendation. To this aim, the user should refer to the corresponding Recommendations, such as [b-ITU-T K.27], [b-ITU-T K.35], [b-ITU-T K.56] and [b-ITU-T K.97].
+
+The lightning protection of service lines, such as power lines and telecommunication lines, is not included in this Recommendation. The information about telecommunication lines is given in [b-ITU-T K.46] and [b-ITU-T K.47].
+
+## 2 References
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- [ITU-T K.39] Recommendation ITU-T K.39 (1996), *Risk assessment of damages to telecommunication sites due to lightning discharges.*
+- [ITU-T K.66] Recommendation ITU-T K.66 (2011), *Protection of customer premises from overvoltage.*
+- [IEC 62305-1] IEC 62305-1 (2010), *Protection against lightning – Part 1: General principles.*
+- [IEC 62305-2] IEC 62305-2 (2010), *Protection against lightning – Part 2: Risk management.*
+- [IEC 62305-3] IEC 62305-3 (2010), *Protection against lightning – Part 3: Physical damage to structures and life hazard.*
+- [IEC 62305-4] IEC 62305-4 (2010), *Protection against lightning – Part 4: Electrical and electronic systems within structures.*
+
+## 3 Definitions
+
+### 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+**3.1.1 conventional earthing impedance** [IEC 62305-1]: Ratio of the peak values of the earth-termination voltage and the earth-termination current which, in general, do not occur simultaneously.
+
+**3.1.2 coordinated SPD system** [IEC 62305-1]: SPDs properly selected, coordinated and installed to form a system intended to reduce failures of electrical and electronic systems.
+
+**3.1.3 dangerous event** [IEC 62305-2]: Lightning flash to or near the structure to be protected, or to or near a line connected to the structure to be protected that may cause damage.
+
+**3.1.4 downward flash** [IEC 62305-1]: Lightning flash initiated by a downward leader from cloud to earth.
+
+NOTE – A downward flash consists of a first impulse, which can be followed by subsequent impulses. One or more impulses may be followed by a long stroke.
+
+**3.1.5 lightning protection level (LPL)** [IEC 62305-1]: Number related to a set of lightning current parameters values relevant to the probability that the associated maximum and minimum design values will not be exceeded in naturally occurring lightning.
+
+NOTE – Lightning protection level is used to design protection measures according to the relevant set of lightning current parameters.
+
+**3.1.6 radio base station** [b-ITU-T K.56]: Installation intended to provide access to the telecommunication system by means of radio waves.
+
+**3.1.7 surge protective device (SPD)** [IEC 62305-1]: Device intended to limit transient overvoltages and divert surge currents; contains at least one non-linear component.
+
+**3.1.8 upward flash** [IEC 62305-1]: Lightning flash initiated by an upward leader from an earthed structure to cloud.
+
+NOTE – An upward flash consists of a first long stroke with or without multiple superimposed impulses. One or more impulses may be followed by a long stroke.
+
+### 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following term:
+
+**3.2.1 common power feed**: A low voltage distribution system which makes the powered buildings and installations interconnected through the same low voltage line.
+
+## 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+EPR Earth Potential Rise
+
+LPL Lightning Protection Level
+
+LPS Lightning Protection System
+
+LV Low Voltage
+
+MV Medium Voltage
+
+RBS Radio Base Station
+
+SPD Surge Protective Device
+
+## 5 Conventions
+
+None.
+
+# 6 Reference configuration
+
+Figure 1 shows the typical layout scenario consisting of the telecommunication tower and the affected surrounding structures (area) in the neighbourhood. In this figure, the possibly affected items are divided into two parts according to the corresponding risk components introduced in Annex A. These two parts can be classified as tower vicinity and local community and are defined as follows:
+
+- **tower vicinity:** Includes the close vicinity around the tower within a limited distance from the edge of the telecommunication site. In this area, the current density and the voltage gradient is much larger than that of the far vicinity. There is the possible risk of injury to living beings by electric shock due to step and touch voltages and/or the hazard resulting from the occurrence of sparking between the tower and the metal parts of adjacent structures.
+- **local community:** Includes the premises and installations connected with the telecommunication site through common low voltage (LV) power feeds, which suffer the influence of transferred surge from the interconnected LV power lines. If the telecommunication site is supplied by a dedicated transformer, the influence of transferred surge through medium voltage (MV) power lines can be negligible.
+
+NOTE 1 – The earth-termination system of the tower shall comply with [IEC 62305-3] and [b-ITU-T K.56].
+
+NOTE 2 – There may be other interconnected lines, such as telecommunication lines, and their influence is under study.
+
+NOTE 3 – If the tower is erected on a rented building, the overall risk re-assessment and protection are needed for the rented building according to the IEC 62305-x series.
+
+![Figure 1 – Reference configuration diagram showing a telecommunication tower, its site, earth grid, and surrounding infrastructure.](a234352dfaccdc24745c88eef7724cc6_img.jpg)
+
+The diagram illustrates a reference configuration for a telecommunication tower. On the left, a 'Telecom tower' is shown with a lightning strike symbol at its top. Below the tower is a 'Telecom site' building. An 'Earth grid' is depicted beneath the site, with an 'EPR' (Earth Potential Rise) curve shown around it. The area immediately surrounding the tower and site is labeled 'Tower vicinity' with dashed vertical lines. To the right, a horizontal line represents 'LV lines' (Low Voltage) leading from the telecom site through an 'SPD' (Surge Protection Device) to a 'Premise'. Further right, another horizontal line represents 'MV lines' (Medium Voltage) leading from a 'Transformer station' to another 'Premise'. The area containing the premises and transformer station is labeled 'Local community' with a horizontal bracket. The diagram is labeled 'K.111(15)\_F01' in the bottom right corner.
+
+Figure 1 – Reference configuration diagram showing a telecommunication tower, its site, earth grid, and surrounding infrastructure.
+
+**Figure 1 – Reference configuration**
+
+# 7 Protection of tower vicinity
+
+### 7.1 Need of protection
+
+The risk assessment shall be performed in order to determine a lightning protection level (LPL) for the determination of safety distances and the design of protection measures.
+
+For the particular application, this Recommendation presents a simplified approach for the evaluation of the protection need based on [IEC 62305-2]. In this approach, the protection needs can be evaluated by considering the frequency of damage ( $F$ ), as described in [ITU-T K.39].
+
+$$F = N_D \cdot P_{dis} \quad (1)$$
+
+where:
+
+$N_D$  is the number of direct flashes to the tower per year
+
+$P_{dis}$  is the protection factor of the safety distance.
+
+When the frequency of damage is greater than the tolerable value ( $F > F_T$ ), then protection measures are necessary. The tolerable frequency of damage value should be defined by the owner of the tower or the authority having jurisdiction according to the hazard level resulting from the occurrence of sparking. For example,  $F_T = 0.05$  means that, on average, 1 damage in 20 years (1/20) is acceptable.
+
+NOTE 1 – Each surrounding structure in the close vicinity of the tower may have different tolerable values.
+
+NOTE 2 – In some countries, the relative authority having jurisdiction may specify the safe separation between the dangerous structures (e.g., gas station, explosive storage building) and the tower directly.
+
+The expected number of direct flashes to the tower per annum ( $N_D$ ) can be evaluated by:
+
+$$N_D = N_G \times \pi \times (3H)^2 \times C_D \times 10^{-6} \quad (2)$$
+
+where:
+
+$N_G$  is the lightning ground flash density (1/km<sup>2</sup> × year)
+
+$H$  is the height of the tower (m)
+
+$C_D$  is the location factor of the tower considering the relative height of the tower with respect to the surrounding objects or the ground within a distance of  $3 \times H$  from the tower (see Table 1).
+
+**Table 1 – Structure location factor  $C_D$**
+
+| Relative location                                         | $C_D$ |
+|-----------------------------------------------------------|-------|
+| Tower surrounded by higher objects                        | 0.25  |
+| Tower surrounded by objects of the same height or shorter | 0.5   |
+| Isolated tower: no other high objects in the vicinity     | 1     |
+| Isolated tower on a hilltop or a knoll                    | 2     |
+
+Under the most severe conditions, the required maximum protection factor ( $P_{dis}'$ ) can be given by the ratio between the tolerable ( $F_T$ ) and expected number of direct flashes to the tower ( $N_D$ ), which is shown by Equation 3:
+
+$$P_{dis}' = F_T / N_D \quad (3)$$
+
+The LPL to be considered in the protection design can be determined by the comparison of  $P_{dis}'$  and  $P_{dis}$  as shown in Table 2. The value of  $P_{dis}$  corresponding to the selected LPL cannot be greater than the  $P_{dis}'$  value calculated by Equation 3. For example, for a value  $P_{dis}' = 0.03$ , the LPL II is at least needed. The lightning parameters associated with LPL are given in Table 3 of clause 7.2.
+
+**Table 2 – Lightning protection level as function of  $P_{dis}$** 
+
+| <b>LPL</b>                                                                                                                                       | <b>I</b> | <b>II</b> | <b>III-IV</b> |
+|--------------------------------------------------------------------------------------------------------------------------------------------------|----------|-----------|---------------|
+| $P_{dis}$                                                                                                                                        | 0.01     | 0.02      | 0.05          |
+| NOTE 1 – If $P_{dis}' < 0.01$ in very severe conditions, one or more protection measures shown in clause 7.3 should be adopted to ensure safety. |          |           |               |
+| NOTE 2 – If $P_{dis}' > 1$ , no protection is needed.                                                                                            |          |           |               |
+
+### 7.2 The assessment of the safety distance
+
+The earth electrodes of the tower should have sufficient separation from existing buried metal parts of structures, cables and metal pipes in the earth to avoid the occurrence of dangerous sparking. From an engineering perspective, this separation is permitted to be relatively rough and conservative. The buried safety distance ( $S_d$ ) can be assessed by Equation 4. In addition, there are some cases in which the metal protrudent parts of structures or cables are close to the tower body or down-conductor. The aerial safety distance ( $S_k$ ) for these cases can be assessed by Equation 5. Figure 2 provides an illustration of these safety distances. The information about the determination of parameters for the assessment is given in Annex B.
+
+$$S_d = (I_{LPL} \cdot Z) / E_{soil} \quad (4)$$
+
+$$S_k = (I_{LPL} \cdot Z + h \cdot L \cdot di/dt) / E_{air} \quad (5)$$
+
+Where:
+
+$S_d$  is the buried safety distance between the earth electrode of the tower and the affected metal objects. In this equation, the peak current of the first positive impulse is considered as  $I_{LPL}$ , according to the selected LPL
+
+$S_k$  is the aerial safety distance between the tower body or down-conductors and the affected metal objects. It is the largest value calculated by the lightning parameters ( $I_{LPL}$  and  $di/dt$ ) of the first positive impulse, the first negative impulse, and subsequent impulse according to the selected LPL
+
+$I_{LPL}$  is the peak current relevant to the LPL to be considered, which is shown in Table B.1
+
+$di/dt$  is the average steepness relevant to the LPL to be considered, which is shown in Table B.1
+
+$E_{air}$  is the breakdown electric field strength of air. The reference value is 600 kV/m
+
+$E_{soil}$  is the breakdown electric field strength of soil. The reference values for types of soil are shown in Table B.2. Where the characteristics of soil are unknown, the average value of  $E_{soil}$  can be chosen as 500 kV/m [b-Zeng].
+
+$Z$  is the conventional earthing impedance of the earth-termination system of the tower. The reference values for typical earthing systems, which comply with [IEC 62305-3], are given in Table B.3
+
+$L$  is the inductance of the tower body. The reference average values of typical towers are given in Table B.4
+
+$h$  is the relevant height, in metres (see Figure 2).
+
+NOTE 1 – It is assumed in the above formula that the earth-termination systems are relatively small so that the voltage drop on the earthing electrodes can be ignored. If this is not the case, more complex equations need to be used.
+
+NOTE 2 – The lightning protection system (LPS) of the tower is seen as an isolated system and the total lightning current is assumed to disperse into the earth-termination system of the tower.
+
+NOTE 3 – If there is other higher insulation material on the surface of these objects or in the interval, the safety distance would be diminished according to the performance of the insulation material.
+
+![Diagram illustrating buried and aerial safety distances (S_k and S_d) between a tower and an affected object.](007b053fe94a8348f75128a584503fd0_img.jpg)
+
+The diagram shows a cross-section of a tower and an affected object (a house) on a ground plane. The tower has a height  $h$  and a point  $A$  is marked on its side. The horizontal separation distance between the tower and the house is labeled  $S_k$ . Below the ground line, the tower's earth electrode and the house's earth electrode are shown. The horizontal separation distance between these two electrodes is labeled  $S_d$ . The ground is indicated by a hatched line. The diagram is labeled K.111(15)\_F02.
+
+Diagram illustrating buried and aerial safety distances (S\_k and S\_d) between a tower and an affected object.
+
+**Figure 2 – Buried and aerial safety distance illustration**
+
+### 7.3 Protection measures
+
+If the separation of the existing or planned configuration is less than the safety distance determined in clause 7.2, one or more of the following four protection measures should be adopted according to field conditions.
+
+#### 1) Expanding the separation
+
+If there is sufficient space available, the separation between the earth electrode of the tower and affected objects should be as great as possible. It is beneficial to try to locate the tower on the opposite side of the earth-termination system. The direction and length of additional horizontal electrodes should be carefully considered in order to not violate the safety distance.
+
+#### 2) Enhancing the insulation of the affected object
+
+If the affected object does not intend to act as an important part of LPS (e.g., pipes, decorative components) or other uncovered elements, an insulation cover (e.g., asphalt, plastics pipe) can be used to enhance the insulation of the affected object. The adequacy of insulation should be confirmed according to the nature of the cover and the actual separation.
+
+#### 3) Adding a segregation layer
+
+For conditions with high ground resistivity or a difficult safe layout, a segregation layer made of insulating material (e.g., asphalt-concrete, asphalt) can be inserted into the soil between the earth electrodes of the tower and the affected objects. Figure 3 shows an illustration regarding this segregation layer.
+
+![Diagram illustrating a segregation layer (asphalt-concrete) of thickness 'b' between an 'Affected object' and an 'Electrode' of a 'Tower'. The diagram shows the tower on the right with an electrode at its base. To the left is an 'Affected object'. A vertical segregation layer of thickness 'b' is placed between them. The distance from the affected object to the edge of the segregation layer is labeled S1. The distance from the edge of the segregation layer to the electrode is labeled S2. The total distance between the affected object and the electrode is labeled S. The diagram is labeled K.111(15)_F03.](0f2a1e4a7b12fe5b8749882ecd636f5c_img.jpg)
+
+Diagram illustrating a segregation layer (asphalt-concrete) of thickness 'b' between an 'Affected object' and an 'Electrode' of a 'Tower'. The diagram shows the tower on the right with an electrode at its base. To the left is an 'Affected object'. A vertical segregation layer of thickness 'b' is placed between them. The distance from the affected object to the edge of the segregation layer is labeled S1. The distance from the edge of the segregation layer to the electrode is labeled S2. The total distance between the affected object and the electrode is labeled S. The diagram is labeled K.111(15)\_F03.
+
+**Figure 3 – Segregation layer to increase the separation distance through the soil**
+
+The breakdown electric field strength of asphalt-concrete is approximately 1500 kV/m. The thickness ( $b$ ) of an asphalt-concrete segregation layer can be determined by Equation 6.
+
+$$b = (I_{LPL} \cdot Z - S \cdot E_{\text{soil}}) / (1500 - E_{\text{soil}}) \quad (6)$$
+
+Where:
+
+$b$  is the thickness of the asphalt-concrete segregation layer
+
+$S$  is the actual distance between the earth electrodes of the tower and the affected object.
+
+The depth and width of the segregation layer should also meet the requirement of Equation 7.
+
+$$S_1 + S_2 + b \geq S_d \quad (7)$$
+
+Where:
+
+$S_1$  is the minimum distance between the edge of the segregation layer and the affected object
+
+$S_2$  is the minimum distance between the edge of segregation layer and the earth electrodes of the tower.
+
+A similar method could be used for the aerial separation, provided that the insulation material has adequate insulating properties.
+
+#### 4) Equipotential bonding
+
+If the affected structure is isolated and not dangerous, equipotential bonding between the electrodes of the tower and the affected parts can be carried out. The efficiency of the connecting materials and the LPS (including external and internal LPS) of the affected structure should be confirmed according to [IEC 62305-3]. Occasionally, for as yet unknown reasons, this measure must be adopted. In this case, the affected structure would be considered as part of the tower system and the expansion of the influence zone of the latter,
+
+due to interconnected electrodes, should be considered. The relevant information is provided in clause 8.
+
+NOTE – Other protection measures for cables can refer to [ITU-T K.47].
+
+### 7.4 Protection measures against injury to living beings due to touch and step voltages
+
+For more detailed information refer to [IEC 62305-3].
+
+# 8 Protection of local community with common power feed
+
+### 8.1 Need of protection
+
+The risk from transferred surges through common power feed is related by many uncertain factors; this has been introduced in clause A.3. The hazard level resulting from this risk also varies over a very wide range. The efficiency of the existing protection measures in these affected structures are difficult to assess; this it is impossible to execute a precise assessment for this risk component.
+
+In order to avoid the excessive workload and waste of investment derived from the protection of every telecommunication tower, it is recommended that the owner of the tower or the authority having jurisdiction on this subject set up a series of exemption criteria. When the telecommunication tower satisfies the exemption criteria, the risk can be considered as negligible.
+
+A typical example of an exemption criteria is shown in the following. If one of the following two rules is fulfilled, the risk from transferred surges through common power feed does not need to be considered.
+
+#### 1) Exemption rule 1
+
+The telecommunication site is served by a dedicated transformer.
+
+NOTE – The lightning protection for a dedicated transformer itself shall conform with the requirements of [b-ITU-T K.110].
+
+#### 2) Exemption rule 2
+
+The expected number of lightning flashes to the tower ( $N_D$ ), that is calculated by Equation 2, is used for this exemption. If  $N_D$  is less than the reference values in Table 3, which depends on the criticalness of the surrounding structures, the site can be exempt from additional lightning protection measures.
+
+**Table 3 – Reference values for exemption based on the expected number of lightning flashes to the tower ( $N_D$ )**
+
+| Criticalness of surrounding structures | Reference $N_D$ value for exemption | Example                       |
+|----------------------------------------|-------------------------------------|-------------------------------|
+| High                                   | 0.01                                | Hospital, Explosive materials |
+| Medium                                 | 0.05                                | Schools                       |
+| Low                                    | 0.1                                 | Residential area              |
+
+NOTE – The criticalness of the surrounding structures shall be selected according to the most important structure or the structure with the most severe prospective hazard.
+
+#### 3) Exemption rule 3
+
+The occurrence rates of dangerous events derived from direct strokes on the LV lines and connected structures ( $S_3$ ) for the LV system can also be used for an exemption criterion. These rates shall be computed for two conditions: (i) considering the presence of the tower ( $S_{3T}$ ) and (ii) disregarding the presence of the tower ( $S_3$ ). If the ratio between  $S_{3T}$  and  $S_3$  is lower than 1.5, then the installation of
+
+the tower does not significantly increase the risk associated with lightning surges conducted by the LV lines, and the influence of the tower could be ignored.
+
+The collection areas under the above conditions could be used for the assessment of  $S_3$  and  $S_{3T}$ . When the structures are sparse and small (e.g., rural environment), only the collection area of LV lines could be considered. When the structures are crowded (e.g., urban environment), only the collection area of the structures could be considered.
+
+NOTE – Annex A of [IEC 62305-2] shall be used for the information about the occurrence rate of dangerous events.
+
+### **8.2 Protection measures**
+
+When a telecommunication tower cannot satisfy the exemption criteria, the following three protection measures should be considered according to field conditions and economic analysis.
+
+#### **1) Adopting dedicated transformer for telecommunication site**
+
+It is proposed to use a dedicated transformer to power the base station, which gives a nearly-total prevention of lightning surge transferring to the nearby local community. This measure is the most effective method, especially for the cases where there are many power-sharing structures and most of the structures cannot be fitted with adequate protection.
+
+#### **2) Reassessment and retrofitting for the affected structures**
+
+When there are only a few structures with common feeds, the reassessment and retrofitting for these existing structures is also a possibility. In some cases, some important or sensitive structures could be selected separately for assessment and protection. The risk assessment and protection requirements should comply with the IEC 62305-x series and [ITU-T K.66].
+
+#### **3) Applicable mitigation measures**
+
+The protection measures may be very difficult to implement in some cases, due to heavy investment or workload, or due to field conditions. For example, some radio base stations (RBSs) are far away from MV lines and the cost of extending the MV line to these stations, in order to install a dedicated transformer, could be unacceptable to the telecommunication operator. In these cases, some mitigation measures can be adopted to decrease the amplitude of the transferred surges, which can reduce the hazard to a low level. These measures are described as follows:
+
+- Reducing earthing resistance (or impedance) of the tower
+
+The earthing resistance (or impedance) of the tower is not of prime importance for lightning protection. However, as introduced in clause A.3, this resistance (or impedance) has an important influence on the surges transferred from the telecommunication site to the local community. In order to reduce these outgoing surges, the earthing resistance (or impedance) shall be as low as possible.
+
+- Adopting shield measures for incoming LV cables of the telecommunication site
+
+Adopting effective shield measures for incoming LV cables of the telecommunication site can remove part of the lightning current from service cables and decrease the amplitude of the transferred current on the live conductors. It is beneficial to relieve the stress of the connected apparatus and surge protective devices (SPDs).
+
+A common shielding technique is to install the cable inside a buried steel pipe or to lay bare conductors (wires) following the LV cables from the earthing system of the tower. The shielding conductors and cables are placed close together in order to reduce the potential difference between them. This measure is expected to carry a larger share of the current, compared to cable shields. The length of the pipe or shielding conductors is to be chosen in such a way that the potential difference developed between the cables and the far-end of the pipe or shielding conductor does not breakdown the cable insulation. In general, the length is recommended to be longer than 50 m. If needed, SPD
+
+should be installed at the junction point between the buried cable and overhead lines, in order to prevent the breakdown of the cable insulation.
+
+## **9 Implementation of protection measures**
+
+The lightning protection of surrounding structures of telecommunication towers is more complex than the protection of a single premise or of the telecommunication site. In most cases, the affected premises and installations are already in place when a telecommunication tower is planned to be erected. The following two aspects should be considered during the life of the tower:
+
+### **1) Construction stage**
+
+- It is important to conduct a field survey to identify the possible affected objects and gather the information about existing conditions;
+- The tower designer should try to select a reasonable location to maintain a safe distance as far as possible from vulnerable structures such as: gas stations, explosive storage, hospitals and the areas accessible to the public;
+- If protection is needed, the designer should try to select the most convenient protection measures, with a minimum disturbance to other inhabitants. For example, when there are many structures with common power feed and most of the structures cannot be provided with adequate protection, a dedicated transformer shall be selected to power the RBS;
+- In cases where the risk cannot be reduced to a tolerable level, some ultimate measures should be adopted, such as relocation or adding cell stations to decrease the height of the tower.
+
+### **2) Operating stage**
+
+- Some artificial measures could be considered, such as adding warning notices and segregation fences;
+- Attention should be given to the new construction of surrounding installations close to the dangerous area;
+- Any inhabitant installation, e.g., TV antennas or metal lines, is prohibited to hang on to or be connected to the tower and should be frequently inspected by maintainers;
+- Sufficient technical explanations should be provided to the public. Occasionally, dialog between the tower owner and surrounding community is necessary in order to avoid unjustified fears.
+
+# Annex A
+
+## Influence on the lightning risk of the surrounding structures due to the presence of a tower
+
+(This annex forms an integral part of this Recommendation.)
+
+### A.1 Possible lightning risk components derived from erection of a tower
+
+For the owner of a tower (e.g., telecommunication operator), the items of most concern are the identification of lightning risk components due to the erection of the tower and the adoption of corresponding protection measures to reduce the risk components to a safe level.
+
+The erection of towers may influence the sources of damage due to lightning for surrounding structures. On the one hand, the height of the tower and the occurrence of a connecting leader from the top of the tower increase the effective collecting area for downward lighting and hence the tower acts as an efficient LPS, protecting the surrounding area from direct lighting strokes. On the other hand, the presence of a tower increases the number of lightning-current pulses that may be applied to a given structure, which may lead to the following sources of accidents:
+
+- earth potential rise (EPR);
+- transfer of transients through common power feeds;
+- induced effects on wiring systems.
+
+As shown in Appendix I, when the tower height is less than 100 m, the lightning ground flash density ( $N_G$ ) in the area where the tower is situated can be considered as unchanged as compared with that of flat ground. For a given surrounding structure, according to the assessment methods introduced in Annex A of [IEC 62305-2], the influence on the sources of damage is analysed as follows:
+
+#### 1) $S_1$ (flashes to a structure)
+
+The occurrence rate of dangerous events about  $S_1$  for the structures in the close vicinity may be decreased due to the protection of towers. However, the occurrence rate of dangerous sparking from a tower may be increased, depending on the separation and the prospective hazard level. Additional information is provided in clause A.2 and clause 7.
+
+#### 2) $S_2$ (flashes near a structure) and $S_4$ (flashes near a line)
+
+The occurrence rate of dangerous events about  $S_2$  and  $S_4$ , which are related with the induced effects on wiring systems, is independent of the tower height. In other words, for a given surrounding structure, the influence of erection of towers on  $S_2$  and  $S_4$  can be ignored.
+
+#### 3) $S_3$ (flashes to a line and to another structure to which a line is connected)
+
+Strictly speaking, the occurrence rate of dangerous events about  $S_3$  should consider not only the total length of the LV line, but also the height and the extension of all the structures served by the same LV system, see [b-Mirra] and [b-IEC TR 62066]. If the telecommunication site belongs to the same LV system and the erection of a tower increases the occurrence rate of dangerous events for this LV system significantly, the influence of the tower should be considered. On the opposite side, if the tower is just one more structure joining the LV system (i.e., it does not increase  $S_3$  significantly), its influence should be ignored.
+
+On the basis of these considerations, the possible risk components derived from the erection of a tower include:
+
+- possible influence on the close vicinity of the tower due to EPR, such as injury to living beings by electric shock due to step and touch voltages, the insulation breakdown between
+
+the tower and the adjacent installations (e.g., reinforcing foundation of building, metal pipes and lines);
+
+- possible influence of transferred transients through common power feeds, which would lead to a partial lightning current flowing to the local community.
+
+Note that the corresponding protection measures intend to reduce the possible risk derived from the erection of towers, but not to improve the overall lightning protection for every surrounding structure. The systemic protection for these structures should refer to the IEC 62305-x series.
+
+Moreover, a misconception about the causes of damage to the surrounding structures should be clarified. In many countries, public complaints about lightning-related events such as property damages and injuries have increased in the region, after the erection of a telecommunication tower. In addition to the influence mechanisms described above, it is important to be aware that these surrounding structures may not have the basic LPSs according to the relevant international or national standards.
+
+### A.2 Risk from EPR on the close vicinity of a tower
+
+When lightning hits a tower, the high lightning current flows into the earth-termination system where the tower is placed, and the earth potential will rise with respect to remote earth. This potential in the area will then decrease monotonically with the distance and depth. The potential decrease can be described according to Figure A.1. Based on a simple approach, the EPR at the lightning-striking point is equal to the maximum lightning current times the impedance of the earth-termination system, and the EPR at a given point is inversely proportional to the distance from the lightning strike point. If the earth impedance increases, the affected region by the EPR will also increase.
+
+![Figure A.1: Distribution of the EPR due to lightning striking a tower. The diagram shows a tower being struck by lightning, with current flowing into the ground. Concentric arcs represent the potential distribution in the earth, decreasing with distance. Below the ground line, a graph shows the potential (V) decreasing as the distance (D) from the electrode increases. The label 'Distance from the electrode' is present.](595e9fd7e96f6b95bbaa6e6a45c32682_img.jpg)
+
+The figure illustrates the distribution of Earth Potential Rise (EPR) following a lightning strike on a tower. At the top, a lightning bolt strikes the top of a tower. The tower is connected to an earth-termination system. Current flows from the tower into the ground. Concentric semi-circular arcs represent the equipotential lines in the earth, showing that the potential decreases as the distance from the strike point increases. Below the ground surface, a graph plots the potential (V) on the vertical axis against the distance (D) from the electrode on the horizontal axis. The curve shows a sharp peak at the electrode (D=0) which decays towards zero as distance increases. The horizontal axis is labeled 'Distance from the electrode' and 'D'. The diagram is labeled 'K.111(15)\_FA.1'.
+
+Figure A.1: Distribution of the EPR due to lightning striking a tower. The diagram shows a tower being struck by lightning, with current flowing into the ground. Concentric arcs represent the potential distribution in the earth, decreasing with distance. Below the ground line, a graph shows the potential (V) decreasing as the distance (D) from the electrode increases. The label 'Distance from the electrode' is present.
+
+Figure A.1 – Distribution of the EPR due to lightning striking a tower
+
+In the far region from the tower, the overvoltages are mainly due to inductive coupling. But in the close vicinity of the tower earthing system, the current density and the voltage gradient attain very high values, which may result in dangerous sparking to nearby metal structures. Field experiments on a group of vertical electrodes have also shown this phenomenon. When the current density  $\delta \geq 0.05 \text{ A/cm}^2$  and soil resistivity  $\rho \geq 2000 \Omega\cdot\text{m}$ , intensive sparking can be observed. When  $\delta \geq 0.5 \text{ A/cm}^2$  and  $\rho \leq 200 \Omega\cdot\text{m}$  for normal soil condition, ground surface sparking has appeared from the electrodes, see [b-Zeng]. In actual circumstances, the adjacent structures are often connected to other structures through metallic lines, which lead to a very low equivalent resistance. As a result, a larger part of the lightning current will flow in this direction, which may enhance the sparking and the stress on the entrance interface of this structure. The amount of transient energy transferred to other connected structures will also be considerably high. Figure A.2 illustrates this phenomenon. At the same time, this dangerous sparking may give rise to physical damage and injury to living beings, as well as to catastrophic consequences to buildings with risk of explosion. In any case, this dangerous sparking should be prevented, as much as possible.
+
+![Diagram illustrating the influence on current dispersion due to an adjacent structure. A lightning strike on a tower creates an Earth Reference Potential (ERP) due to lightning. This potential is shown on the ground surface near a house. A red lightning bolt symbol indicates sparking occurring between the ground near the tower and the ground near the house. A red line labeled 'Conduct through SPD or arcing' shows the current path from the tower's earthing system, through a house's internal wiring (represented by a zigzag line), to the house's earthing system. The diagram is labeled K.111(15)_FA.2.](7f25db95ce3916c0e09803b861a2f7bc_img.jpg)
+
+Diagram illustrating the influence on current dispersion due to an adjacent structure. A lightning strike on a tower creates an Earth Reference Potential (ERP) due to lightning. This potential is shown on the ground surface near a house. A red lightning bolt symbol indicates sparking occurring between the ground near the tower and the ground near the house. A red line labeled 'Conduct through SPD or arcing' shows the current path from the tower's earthing system, through a house's internal wiring (represented by a zigzag line), to the house's earthing system. The diagram is labeled K.111(15)\_FA.2.
+
+**Figure A.2 – Influence on current dispersion due to an adjacent structure**
+
+Even if the electric fields are not sufficiently high enough to generate sparking, the current flow close to the ground surface may also give rise to step potential hazards when human beings and animals stand on the ground.
+
+Because the distribution of EPR is related to the amplitude and shape of the lightning current, characteristics of the earthing grid, soil resistivity, soil dielectric constant and other factors, it is very difficult to carry out a precise calculation. However, from an engineering perspective, it is necessary to regulate sufficient separation (safety distance) from these existing metallic parts of structures, cables and metal pipes in the earth to avoid the occurrence of dangerous sparking. This separation is permitted to be relatively rough and conservative. At the same time, the LPSs of towers should make special provisions for protection against dangerous step voltages or touch voltages in the vicinity of the earth-termination networks, if they are installed in areas accessible to the public.
+
+### A.3 Risk from transferred surge through common power feed
+
+Telecommunication towers and the equipment building of an RBS are not isolated systems. Usually, many cables, including power cables, enter the building from the local community network. A typical scenario is shown in Figure A.3. When the tower is hit by a lightning flash, the earth potential at the tower and associated RBS may be extremely high compared with that in the ground of the interconnected metallic system supplying the nearby structures. The high potential difference drives large surge currents via service cables to the local community, where it gets distributed to these
+
+structures. Consequently, for a given flash density in the area, the presence of a tower, although reducing the probability of direct flashes to smaller buildings in its vicinity, enhances the probability of conducted overvoltages.
+
+![Diagram illustrating the typical configuration including a local community. A central 'Tower' is shown with 'Radial conductors' and a 'Ring conductor' connected to it. 'Tower cables' and an 'Earth conductor' lead from the tower to a 'Building'. The 'Building' is connected to a 'Ring conductor' and 'Service cables'. The 'Service cables' lead to a 'Local community' represented by a green oval. The diagram is labeled K.111(15)_FA.3.](83852ec55d4802521a727926336bedab_img.jpg)
+
+Diagram illustrating the typical configuration including a local community. A central 'Tower' is shown with 'Radial conductors' and a 'Ring conductor' connected to it. 'Tower cables' and an 'Earth conductor' lead from the tower to a 'Building'. The 'Building' is connected to a 'Ring conductor' and 'Service cables'. The 'Service cables' lead to a 'Local community' represented by a green oval. The diagram is labeled K.111(15)\_FA.3.
+
+**Figure A.3 – Typical configuration including local community**
+
+In an actual situation, the LV power distribution system is the most critical common dispersion route. The surrounding premises and installations sharing a mutual transformer with the tower site can all be affected. The transferred overvoltage and partial lightning current along the LV distribution lines will stress all of the connected apparatus and SPDs in the interconnected structures. At first glance, the most threatening situation would be the overvoltages between conductors and local earth applied to the power equipment. In addition, these transferred overvoltages may lead to overvoltages between the power system and the communications system connected to the same equipment. Field investigations have revealed that this coupling path is also the common damage mechanism.
+
+Depending on the division of the lightning current, the configuration of the LV distribution system, earthing practices and the presence or absence of SPDs, the transferred overvoltage can be large or moderate. Because all the above factors vary over a wide range according to the general practice of the utility, as well as local configurations, it is impossible to present a quantitative calculation for all types of systems.
+
+The division of the lightning current is mostly determined by the ratio of the resistances between the tower and local community, as described in [b-IEC 61643-12], [b-IEC TR 62066]. As a result, the worse the earthing condition of the tower or the higher the density of the mutual feeding buildings in an area, the greater the portion of the lightning current that would flow out of the telecommunication site through the incoming LV power cable.
+
+NOTE – The above current division is suitable for 10/350  $\mu\text{s}$  as defined in [IEC 62305-1]. In the initial phase of lightning current, the current division is determined by the ratio of the inductances. In the tail, where the current time-derivative is low, the division is determined by the ratio of the resistances. For cases where the waveform is much shorter than 10/350  $\mu\text{s}$ , the current division cannot be simply assessed by considering only the resistances.
+
+Different practices of earthing the neutral are found in different countries, so that some difference can be expected in the way the lightning current will disperse among the available paths. As a result, the transferred overvoltages will also be different, according to the actual configuration of the LV distribution system. For example, in a TN-C system, because the phase-to-earth voltage is much less attenuated than the neutral-to-earth voltage due to the multiple earthing connections of the neutral conductor, a significant phase-to-neutral voltage builds up as the distance from the BS increases. This is why the damage may be more severe when the structure is far from the BS in some actual incidents.
+
+However, if the telecommunication site is served by a dedicated transformer, the flow of lightning current through the MV power system should have negligible consequences to the local community. Figure A.4 shows two typical configurations with dedicated transformers. In the left-hand side the transformer is installed outside the building and connected to the RBS (Telecom site) through an external LV cable, while in the right-hand side the transformer is installed inside the building that contains the telecommunication equipment (RBS).
+
+![Diagram showing two typical configurations with dedicated transformers for telecommunication sites.](812e188283162af0b54fb3e30ffee51b_img.jpg)
+
+The diagram illustrates two typical configurations for telecommunication sites with dedicated transformers. Both configurations show a 'Telecom tower' on the left, a 'Telecom site' (or 'Building'), a 'Transformer', and an 'Earth grid'.
+
+**Left Configuration:** The 'Telecom tower' is connected to the 'Telecom site' building. The 'Transformer' is located outside the building, connected to the 'Telecom site' by an 'LV cable'. The 'Transformer' is also connected to the 'Earth grid' by an 'MV cable'.
+
+**Right Configuration:** The 'Telecom tower' is connected to the 'Building' (which contains the 'Telecom site'). The 'Transformer' is located inside the 'Building', connected to the 'Telecom site' by an 'LV cable'. The 'Transformer' is also connected to the 'Earth grid' by an 'MV cable'.
+
+Labels in the diagram include: 'Telecom tower', 'Telecom site', 'Transformer', 'MV cable', 'LV cable', 'Earth grid', and 'Building'. A reference code 'K.111(15)\_FA.4' is present in the bottom right corner of the diagram area.
+
+Diagram showing two typical configurations with dedicated transformers for telecommunication sites.
+
+**Figure A.4 – Two typical configurations with dedicated transformers**
+
+# Annex B
+
+## Determination of parameters for the assessment of safety distance
+
+(This annex forms an integral part of this Recommendation.)
+
+### B.1 Lightning parameters according to LPL
+
+The corresponding lightning parameters related to LPL are given by [IEC 62305-1]. Table B.1 shows some lightning stroke parameters associated with each LPL.
+
+**Table B.1 – Lightning parameters according to LPL from [IEC 62305-1]**
+
+| Parameter                                                              | Unit              | LPL |      |          |
+|------------------------------------------------------------------------|-------------------|-----|------|----------|
+|                                                                        |                   | I   | II   | III – IV |
+| Maximum peak current of first positive impulse (10/350 $\mu\text{s}$ ) | kA                | 200 | 150  | 100      |
+| Maximum peak current of first negative impulse (1/200 $\mu\text{s}$ )  | kA                | 100 | 75   | 50       |
+| Maximum peak current of subsequent impulse (0.25/100 $\mu\text{s}$ )   | kA                | 50  | 37.5 | 25       |
+| Average steepness of first positive impulse ( $di/dt$ )                | kA/ $\mu\text{s}$ | 20  | 15   | 10       |
+| Average steepness of first negative impulse ( $di/dt$ )                | kA/ $\mu\text{s}$ | 100 | 75   | 50       |
+| Average steepness of subsequent impulse ( $di/dt$ )                    | kA/ $\mu\text{s}$ | 200 | 150  | 100      |
+
+### B.2 Reference values of $E_{\text{soil}}$
+
+The reference value of the breakdown electric field strength ( $E_{\text{soil}}$ ) of soil under different types of soil and soil resistivity are shown in Table B.2.
+
+**Table B.2 – The referring value of  $E_{\text{soil}}$  under different soil property and resistivity [b-Huai]**
+
+| Soil property | Soil resistivity<br>( $\Omega\cdot\text{m}$ ) | $E_{\text{soil}}$<br>(kV/cm) |
+|---------------|-----------------------------------------------|------------------------------|
+| clay          | 2700                                          | 16                           |
+|               | 1000                                          | 14.4                         |
+|               | 250                                           | 8.4                          |
+|               | 160                                           | 9                            |
+|               | 140                                           | 10.4                         |
+|               | 120                                           | 8.2                          |
+|               | 70                                            | 7.4                          |
+| humus         | 1050                                          | 4.2                          |
+|               | 550                                           | 7.2                          |
+|               | 350                                           | 5.8                          |
+|               | 90                                            | 9.2                          |
+|               | 35                                            | 9.6                          |
+|               | 22                                            | 4.5                          |
+| sandy soil    | 45~3400                                       | 12.8~13.8                    |
+
+### B.3 Reference values of typical earthing impedance
+
+The referring values for typical earthing systems, which comply with [IEC 62305-3], are given in Table B.3. Other available methods defined in national regulations are also permitted.
+
+**Table B.3 – Conventional earthing impedance values  $Z$  according to [IEC 62305-3], for different soil resistivities**
+
+| Soil resistivity<br>( $\Omega \cdot \text{m}$ ) | Conventional earthing impedance ( $Z$ ) related to the type of LPS<br>( $\Omega$ ) |    |          |
+|-------------------------------------------------|------------------------------------------------------------------------------------|----|----------|
+|                                                 | I                                                                                  | II | III – IV |
+| $\leq 100$                                      | 4                                                                                  | 4  | 4        |
+| 200                                             | 6                                                                                  | 6  | 6        |
+| 500                                             | 10                                                                                 | 10 | 10       |
+| 1000                                            | 10                                                                                 | 15 | 20       |
+| 2000                                            | 10                                                                                 | 15 | 40       |
+| 3000                                            | 10                                                                                 | 15 | 60       |
+
+NOTE 1 – Values reported in this table refer to the conventional earthing impedance of a buried conductor under impulse condition (10/350  $\mu\text{s}$ ).  
+NOTE 2 – Earthing system complying with clause 5.4 of [IEC 62305-3].
+
+### B.4 Reference values of tower inductance
+
+The reference average values of the inductance ( $L$ ) of the tower body for different types of towers are given in Table B.4. These values are intended to be used in order to determine the safety distances according to this Recommendation (see clause 7.2).
+
+**Table B.4 – The referring average values  $L$  of the inductance of tower body [b-Huai]**
+
+| Tower type                      | The referring average value<br>( $\mu\text{H} \cdot \text{m}$ ) |
+|---------------------------------|-----------------------------------------------------------------|
+| Tubular tower                   | 0.84                                                            |
+| Tubular tower with stay wires   | 0.42                                                            |
+| Three-leg tower                 | 0.70                                                            |
+| Three-leg tower with stay wires | 0.35                                                            |
+| Four-leg tower                  | 0.50                                                            |
+
+# Appendix I
+
+## Influence of the tower on the ground flash density
+
+(This appendix does not form an integral part of this Recommendation.)
+
+For a tall structure, there may be two basic types of flashes of concern:
+
+- downward flashes initiated by a downward leader from cloud to earth;
+- upward flashes initiated by an upward leader from an earthed structure to cloud.
+
+Most downward flashes occur in flat territory, and to lower structures, whereas for exposed and/or higher structures upward flashes become dominant. The relative information about possible components of these two categories is given by [IEC 62305-1].
+
+### I.1 Downward flash
+
+The most common form of downward flash is a multiple-stroke negative flash. The negatively charged leader, initiated after a preliminary discharge in the cloud, descends towards the ground in a stepped manner from the thundercloud. This stepped leader is highly branched (tortuous) due to randomly distributed space charge between the cloud and the earth. When this stepped leader propagates towards the ground, the field at the ground or grounded objects gradually increases. When the field reaches a critical value on the ground or grounded structures, upward leaders originate from them and propagate towards the tip of the descending stepped leader. The inception of the upward leaders from the tip of the structures is largely dependent on the level of field enhancement at the structure tips, predominantly governed by the structure geometry (heights and radii), the proximity of other structures, the background electric field due to the cloud, and the descending stepped leader charge. A strike is established when one of the upward leaders succeeds in establishing a contact with a descending stepped leader. At this junction, an intensive current wave, termed as return stroke, travels upward. It is this phase that is most hazardous because of the associated large transient currents and field changes. As the charge on the leader will be neutralized by the return stroke current wave, it is possible to relate the peak amplitude of the return stroke current with the charge on the leader.
+
+Upward leaders from tall towers, in response to descending stepped leaders, ensure that lightning strikes the tower rather than the nearby ground. This is the same principle as the lightning rod in LPS of buildings. In principle, a tall tower on flat ground tends to attract the lightning flashes that would have struck the nearby ground.
+
+### I.2 Upward flash
+
+The situation may be different when towers are placed on high hills or if the tower is extremely tall. The background electric field on the top of a hill under a thundercloud is high and when a tower is placed on that hill, the tower enhances the field even more. In such cases, the electrical discharges, happening inside the cloud or the cloud charges, may cause the launching of an upward leader from the tower, even without a downward moving leader at the beginning. If this upward leader travels all the way to the cloud and initiates a cloud-to-ground lightning to the tower, it results in an upward flash. This lightning flash would not have happened if the tower was not present. Therefore, in such cases, it is possible to say that the presence of the tower causes an increase in the number of lightning strikes to that area.
+
+The initiating condition of upward flashes is related to ambient field on the ground due to the cloud and to the structure height. It is valid to speak in terms of ambient ground field because of the uncertainty that exists in knowing the position of the cloud and the cloud potential itself. In rocket-triggered lightning it has been observed that the ground electric field at the time of triggering a flash by the rocket is between 5 and 15 kV/m, and very rarely it exceeds 15 kV/m, see [b-Theethayi]. From the analysis of measurements and theoretical considerations, see [b-Theethayi], [b-Chandimal], the
+
+tower height corresponding to a critical ambient ground field of 15 kV/m is approximately 100 m on flat ground. Thus, it is suggested that towers on level ground with heights below about 100 m on flat ground do not normally experience upward flashes. It should be pointed out that a tower shorter than 100 m can also initiate upward lighting if it is situated on a mountain ridge or high hill.
+
+In general, as far as a downward lightning is concerned, the tower is acting like a huge lightning rod with a large protective area, and does not really increase the number of downward lightning flashes. It is the upward flashes that increase the lightning incidence to the tower and therefore, it can be inferred that towers less than 100 m high, on flat ground, do not increase the incidence of lightning.
+
+In practical engineering, the circumstance of telecommunication towers placed in residential neighbourhoods rarely meet the initiation condition of upward flashes. Hence, it is highly unlikely that the occurrence of lightning strikes per year for the defined area increases due to the existence of the tower. This means that the lightning ground flash density ( $N_G$ ) has not been changed due to the presence of the tower.
+
+## Bibliography
+
+- [b-ITU-T K.27] Recommendation ITU-T K.27 (1996), *Bonding configurations and earthing inside a telecommunication building*.
+- [b-ITU-T K.35] Recommendation ITU-T K.35 (1996), *Bonding configurations and earthing at remote electronic sites*.
+- [b-ITU-T K.46] Recommendation ITU-T K.46 (2012), *Protection of telecommunication lines using metallic symmetric conductors against lightning-induced surges*.
+- [b-ITU-T K.47] Recommendation ITU-T K.47 (2008), *Protection of telecommunication lines using metallic conductors against direct lightning discharges*.
+- [b-ITU-T K.56] Recommendation ITU-T K.56 (2010), *Protection of radio base stations against lightning discharges*.
+- [b-ITU-T K.97] Recommendation ITU-T K.97 (2014), *Lightning protection of distributed base stations*.
+- [b-ITU-T K.110] Recommendation ITU-T K.110 (2015), *Lightning protection of the dedicated transformer for radio base stations*.
+- [b-IEC 61643-12] IEC 61643-12 (2008), *Low-voltage surge protective devices – Part 12: Surge protective devices connected to low-voltage power distribution systems – Selection and application principles*.
+- [b-IEC TR 62066] IEC TR 62066 (2006), *Surge overvoltages and surge protection in low-voltage a.c. power systems – General basic information*.
+- [b-Chandimal] A.P.L. Chandimal, Chandima Gomes (2012), *Lightning related effects on the neighborhood of telecommunication tower sites*, International Conference on Lightning Protection (ICLP), Vienna, Austria.
+- [b-Huai] Du Song Huai, Zhang You Hui (2011), *Grounding technology in power system*, China water industry and power system Press.
+- [b-Mirra] C. Mirra, A. Porrino, A. Ardito, C.A. Nucci (1997), *Lightning overvoltages in low-voltage networks*, 14th CIRED conference, paper 2.19, Publ. No. 438, Birmingham, U.K., June.
+- [b-Theethayi] N. Theethayi, and R. Thottappillii (2007), *Some issues concerning lightning strikes to communication towers*, Journal of Electrostatics, Vol. 65, pp. 689-703.
+- [b-Zeng] Zeng Yong Lin (1989), *Earthing technology*, China Water Industry and Power System Press.
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+|                 |                                                                                                                                                           |
+|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Series A        | Organization of the work of ITU-T                                                                                                                         |
+| Series D        | General tariff principles                                                                                                                                 |
+| Series E        | Overall network operation, telephone service, service operation and human factors                                                                         |
+| Series F        | Non-telephone telecommunication services                                                                                                                  |
+| Series G        | Transmission systems and media, digital systems and networks                                                                                              |
+| Series H        | Audiovisual and multimedia systems                                                                                                                        |
+| Series I        | Integrated services digital network                                                                                                                       |
+| Series J        | Cable networks and transmission of television, sound programme and other multimedia signals                                                               |
+| <b>Series K</b> | <b>Protection against interference</b>                                                                                                                    |
+| Series L        | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant |
+| Series M        | Telecommunication management, including TMN and network maintenance                                                                                       |
+| Series N        | Maintenance: international sound programme and television transmission circuits                                                                           |
+| Series O        | Specifications of measuring equipment                                                                                                                     |
+| Series P        | Terminals and subjective and objective assessment methods                                                                                                 |
+| Series Q        | Switching and signalling                                                                                                                                  |
+| Series R        | Telegraph transmission                                                                                                                                    |
+| Series S        | Telegraph services terminal equipment                                                                                                                     |
+| Series T        | Terminals for telematic services                                                                                                                          |
+| Series U        | Telegraph switching                                                                                                                                       |
+| Series V        | Data communication over the telephone network                                                                                                             |
+| Series X        | Data networks, open system communications and security                                                                                                    |
+| Series Y        | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities                               |
+| Series Z        | Languages and general software aspects for telecommunication systems                                                                                      |