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Chapter 2 Wiring and Protection
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250.28(D)(2)
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If a service consists of more than a single enclosure as permitted in 230.71(B), the main bonding jumper for each enclosure shall be sized in accordance with 250.28(D)(1) based on the largest ungrounded service conductor serving that enclosure. [250.28(D)(2)](https://2023.antflix.net#250.28(D)(2))
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https://2023.antflix.net#250.28(D)(2)
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Chapter 2 Wiring and Protection
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250.28(D)(3)
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If a separately derived system supplies more than a single enclosure, the system bonding jumper for each enclosure shall be sized in accordance with 250.28(D)(1) based on the largest ungrounded feeder conductor serving that enclosure, or a single system bonding jumper shall be installed at the source and sized in accordance with 250.28(D)(1) based on the equivalent size of the largest supply conductor determined by the largest sum of the areas of the corresponding conductors of each set. [250.28(D)(3)](https://2023.antflix.net#250.28(D)(3))
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https://2023.antflix.net#250.28(D)(3)
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Chapter 2 Wiring and Protection
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250.30
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In addition to complying with 250.30(A) for grounded systems, or as provided in 250.30(B) for ungrounded systems, separately derived systems shall comply with 250.20, 250.21, or 250.26, as applicable. Multiple power sources of the same type that are connected in parallel to form one system that supplies premises wiring shall be treated as a single separately derived system and shall be installed in accordance with 250.30. Informational Note No. 1: An alternate ac power source, such as an on-site generator, is not a separately derived system if the grounded conductor is solidly interconnected to a service-supplied system grounded conductor. An example of such a situation is if the alternate source transfer equipment does not include a switching action in the grounded conductor and allows it to remain solidly connected to the service-supplied grounded conductor when the alternate source is operational and supplying the load served. Informational Note No. 2: See 445.13 for the minimum size of conductors that carry fault current. [250.30](https://2023.antflix.net#250.30)
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https://2023.antflix.net#250.30
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Chapter 2 Wiring and Protection
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250.30(A)
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A separately derived ac system that is grounded shall comply with 250.30(A)(1) through (A)(8). Except as otherwise permitted in this article, a grounded conductor shall not be connected to normally non-current-carrying metal parts of equipment, be connected to equipment grounding conductors, or be reconnected to ground on the load side of the system bonding jumper. Informational Note: See 250.32 for connections at separate buildings or structures and 250.142 for use of the grounded circuit conductor for grounding equipment. Exception: Impedance grounded system grounding connections shall be made in accordance with 250.36 or 250.187, as applicable. [250.30(A)](https://2023.antflix.net#250.30(A))
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https://2023.antflix.net#250.30(A)
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Chapter 2 Wiring and Protection
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250.30(A)(1)
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An unspliced system bonding jumper shall comply with 250.28(A) through (D). This connection shall be made at any single point on the separately derived system from the source to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices, in accordance with 250.30(A)(1)(a) or (A)(1)(b). The system bonding jumper shall remain within the enclosure where it originates. If the source is located outside the building or structure supplied, a system bonding jumper shall be installed at the grounding electrode connection in compliance with 250.30(C). Exception No. 1: For systems installed in accordance with 450.6, a single system bonding jumper connection to the tie point of the grounded circuit conductors from each power source shall be permitted. Exception No. 2: If a building or structure is supplied by a feeder from an outdoor separately derived system, a system bonding jumper at both the source and the first disconnecting means shall be permitted if doing so does not establish a parallel path for the grounded conductor. If a grounded conductor is used in this manner, it shall not be smaller than the size specified for the system bonding jumper but shall not be required to be larger than the ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as providing a parallel path. Exception No. 3: The size of the system bonding jumper for a system that supplies a Class 1, Class 2, or Class 3 circuit, and is derived from a transformer rated not more than 1000 volt-amperes, shall not be smaller than the derived ungrounded conductors and shall not be smaller than 14 AWG copper or 12 AWG aluminum.Installed at the Source. The system bonding jumper shall connect the grounded conductor to the supply-side bonding jumper and the normally non-current-carrying metal enclosure.Installed at the First Disconnecting Means. The system bonding jumper shall connect the grounded conductor to the supply-side bonding jumper, the disconnecting means enclosure, and the equipment grounding conductor(s).Exception: Separately derived systems consisting of multiple sources of the same type that are connected in parallel shall be permitted to have the system bonding jumper installed at the paralleling switchgear, switchboard, or other paralleling connection point instead of at the disconnecting means located at each separate source. [250.30(A)(1)](https://2023.antflix.net#250.30(A)(1))
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https://2023.antflix.net#250.30(A)(1)
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Chapter 2 Wiring and Protection
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250.30(A)(2)
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If the source of a separately derived system and the first disconnecting means are located in separate enclosures, a supply-side bonding jumper shall be installed with the circuit conductors from the source enclosure to the first disconnecting means enclosure. A supply-side bonding jumper shall not be required to be larger than the derived ungrounded conductors. The supply-side bonding jumper shall be permitted to be of nonflexible metal raceway type or of the wire or bus type as follows: A supply-side bonding jumper of the wire type shall comply with 250.102(C), based on the size of the derived ungrounded conductors.A supply-side bonding jumper of the bus type shall have a cross-sectional area not smaller than a supply-side bonding jumper of the wire type as determined in 250.102(C).Exception: A supply-side bonding jumper shall not be required between enclosures for installations made in compliance with 250.30(A)(1), Exception No. 2. [250.30(A)(2)](https://2023.antflix.net#250.30(A)(2))
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https://2023.antflix.net#250.30(A)(2)
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Chapter 2 Wiring and Protection
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250.30(A)(3)
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If a grounded conductor is installed and the system bonding jumper connection is not located at the source, 250.30(A)(3)(a) through (A)(3)(d) shall apply. The grounded conductor shall not be required to be larger than the derived ungrounded conductors. Sizing for a Single Raceway. The grounded conductor shall not be smaller than specified in Table 250.102(C)(1).Conductors Connected in Parallel in Two or More Raceways or Cables. If the ungrounded conductors are connected in parallel in two or more raceways or cables, the grounded conductors shall also be installed in each raceway or cable and shall be connected in parallel. The size of the grounded conductor(s) in each raceway or cable shall be based on the largest derived ungrounded conductor in each raceway or cable, or the sum of the circular mil areas of the largest derived ungrounded conductors from each set connected in parallel in each raceway or cable, in accordance with 250.30(A)(3)(a), but not smaller than 1/0 AWG.Informational Note: See 310.10(G) for grounded conductors connected in parallel.Delta-Connected System. The grounded conductor of a 3-phase, 3-wire delta system shall have an ampacity not less than that of the ungrounded conductors.Impedance Grounded System. The impedance grounding conductor of an impedance grounded system shall be installed in accordance with 250.36 or 250.187, as applicable. [250.30(A)(3)](https://2023.antflix.net#250.30(A)(3))
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https://2023.antflix.net#250.30(A)(3)
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Chapter 2 Wiring and Protection
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250.30(A)(4)
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The building or structure grounding electrode system shall be used as the grounding electrode for the separately derived system. If located outdoors, the grounding electrode shall be in accordance with 250.30(C). Exception: If a separately derived system originates in equipment that is listed and identified as suitable for use as service equipment, the grounding electrode used for the service or feeder equipment shall be permitted to be used as the grounding electrode for the separately derived system. Informational Note No. 1: See 250.104(D) for bonding requirements for interior metal water piping in the area served by separately derived systems. Informational Note No. 2: See 250.50 and 250.58 for requirements for bonding all electrodes together if located at the same building or structure. [250.30(A)(4)](https://2023.antflix.net#250.30(A)(4))
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https://2023.antflix.net#250.30(A)(4)
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Chapter 2 Wiring and Protection
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250.30(A)(5)
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A grounding electrode conductor for a single separately derived system shall be sized in accordance with 250.66 for the derived ungrounded conductors. It shall be used to connect the grounded conductor of the derived system to the grounding electrode in accordance with 250.30(A)(4), or as permitted in 250.68(C)(1) and (C)(2). This connection shall be made at the same point on the separately derived system where the system bonding jumper is connected. Exception No. 1: If the system bonding jumper specified in 250.30(A)(1) is a wire or busbar, it shall be permitted to connect the grounding electrode conductor to the equipment grounding terminal, bar, or bus if the equipment grounding terminal, bar, or bus is of sufficient size for the separately derived system. Exception No. 2: If the source of a separately derived system is located within equipment listed and identified as suitable for use as service equipment, the grounding electrode conductor from the service or feeder equipment to the grounding electrode shall be permitted as the grounding electrode conductor for the separately derived system, if the grounding electrode conductor is of sufficient size for the separately derived system. If the equipment grounding bus internal to the equipment is not smaller than the required grounding electrode conductor for the separately derived system, the grounding electrode connection for the separately derived system shall be permitted to be made to the bus. Exception No. 3: A grounding electrode conductor shall not be required for a system that supplies a Class 1, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes, provided the grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with 250.30(A)(1), Exception No. 3, and the transformer frame or enclosure is grounded by one of the means specified in 250.134. [250.30(A)(5)](https://2023.antflix.net#250.30(A)(5))
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https://2023.antflix.net#250.30(A)(5)
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Chapter 2 Wiring and Protection
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250.30(A)(6)
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A common grounding electrode conductor for multiple separately derived systems shall be permitted. If installed, the common grounding electrode conductor shall be used to connect the grounded conductor of each separately derived system to the grounding electrode as specified in 250.30(A)(4). A grounding electrode conductor tap shall then be installed from each separately derived system to the common grounding electrode conductor. Each tap conductor shall connect the grounded conductor of the separately derived system to the common grounding electrode conductor. This connection shall be made at the same point on the separately derived system where the system bonding jumper is connected. Exception No. 1: If the system bonding jumper specified in 250.30(A)(1) is a wire or busbar, it shall be permitted to connect the grounding electrode conductor tap to the equipment grounding terminal, bar, or bus, provided the equipment grounding terminal, bar, or bus is of sufficient size for the separately derived system. Exception No. 2: A grounding electrode conductor shall not be required for a system that supplies a Class 1, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes, provided the system grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with 250.30(A)(1), Exception No. 3, and the transformer frame or enclosure is grounded by one of the means specified in 250.134. Exception No. 3: If the source of a separately derived system is located within equipment listed and identified as suitable for use as service equipment, the grounding electrode conductor from the service or feeder equipment to the grounding electrode shall be permitted as the grounding electrode conductor for the separately derived system, if the grounding electrode conductor is of sufficient size for the separately derived system. If the equipment grounding bus internal to the equipment is not smaller than the required grounding electrode conductor for the separately derived system, the grounding electrode connection for the separately derived system shall be permitted to be made to the bus.Common Grounding Electrode Conductor. The common grounding electrode conductor shall be permitted to be one of the following:A conductor of the wire type not smaller than 3/0 AWG copper or 250 kcmil aluminumA metal water pipe in accordance with 250.68(C)(1)The metal structural frame of the building or structure in accordance with 250.68(C)(2) or is connected to the grounding electrode system by a conductor not smaller than 3/0 AWG copper or 250 kcmil aluminumTap Conductor Size. Each tap conductor shall be sized in accordance with 250.66 based on the derived ungrounded conductors of the separately derived system it serves.Exception to (a)(1) and (b): If the only electrodes that are present are of the types in 250.66(A), (B), or (C), the size of the common grounding electrode conductor shall not be required to be larger than the largest conductor required by 250.66(A), (B), or (C) for the type of electrode that is present.Connections. All tap connections to the common grounding electrode conductor shall be made at an accessible location by one of the following methods:A connector listed as grounding and bonding equipment.Listed connections to aluminum or copper busbars not smaller than 6 mm thick × 50 mm wide (1/4 in. thick × 2 in. wide) and of a length to accommodate the number of terminations necessary for the installation. If aluminum busbars are used, the installation shall also be in accordance with 250.64(A).The exothermic welding process.Tap conductors shall be connected to the common grounding electrode conductor in such a manner that the common grounding electrode conductor remains without a splice or joint. [250.30(A)(6)](https://2023.antflix.net#250.30(A)(6))
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https://2023.antflix.net#250.30(A)(6)
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Chapter 2 Wiring and Protection
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250.30(A)(7)
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The installation of all grounding electrode conductors shall comply with 250.64(A), (B), (C), and (E). [250.30(A)(7)](https://2023.antflix.net#250.30(A)(7))
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https://2023.antflix.net#250.30(A)(7)
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Chapter 2 Wiring and Protection
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250.30(A)(8)
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Structural steel and metal piping shall be connected to the grounded conductor of a separately derived system in accordance with 250.104(D). [250.30(A)(8)](https://2023.antflix.net#250.30(A)(8))
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https://2023.antflix.net#250.30(A)(8)
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Chapter 2 Wiring and Protection
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250.30(B)
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The equipment of an ungrounded separately derived system shall be grounded and bonded as specified in 250.30(B)(1) through (B)(3). [250.30(B)](https://2023.antflix.net#250.30(B))
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https://2023.antflix.net#250.30(B)
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Chapter 2 Wiring and Protection
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250.30(B)(1)
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A grounding electrode conductor, sized in accordance with 250.66 for the largest derived ungrounded conductor(s) or set of derived ungrounded conductors, shall be used to connect the metal enclosures of the derived system to the grounding electrode as specified in 250.30(A)(5) or (A)(6), as applicable. This connection shall be made at any point on the separately derived system from the source to the first system disconnecting means. If the source is located outside the building or structure supplied, a grounding electrode connection shall be made in compliance with 250.30(C). [250.30(B)(1)](https://2023.antflix.net#250.30(B)(1))
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https://2023.antflix.net#250.30(B)(1)
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Chapter 2 Wiring and Protection
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250.30(B)(2)
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Except as permitted by 250.34 for portable and vehicle-mounted generators, the grounding electrode shall comply with 250.30(A)(4). [250.30(B)(2)](https://2023.antflix.net#250.30(B)(2))
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https://2023.antflix.net#250.30(B)(2)
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Chapter 2 Wiring and Protection
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250.30(B)(3)
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A supply-side bonding jumper shall be installed from the source of a separately derived system to the first disconnecting means in compliance with 250.30(A)(2). [250.30(B)(3)](https://2023.antflix.net#250.30(B)(3))
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https://2023.antflix.net#250.30(B)(3)
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Chapter 2 Wiring and Protection
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250.30(C)
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If the source of the separately derived system is located outside the building or structure supplied, a grounding electrode connection shall be made at the source location to one or more grounding electrodes in accordance with 250.50. In addition, the installation shall be in accordance with 250.30(A) for grounded systems or with 250.30(B) for ungrounded systems. Exception: The grounding electrode conductor connection for impedance grounded systems shall be in accordance with 250.36 or 250.187, as applicable. [250.30(C)](https://2023.antflix.net#250.30(C))
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https://2023.antflix.net#250.30(C)
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Chapter 2 Wiring and Protection
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250.32(A)
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A building(s) or structure(s) supplied by a feeder(s) or branch circuit(s) shall have a grounding electrode system and grounding electrode conductor installed in accordance with Part III of Article 250. Exception: A grounding electrode system and grounding electrode conductor shall not be required if only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non-current-carrying metal parts of equipment. [250.32(A)](https://2023.antflix.net#250.32(A))
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https://2023.antflix.net#250.32(A)
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Chapter 2 Wiring and Protection
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250.32(B)(1)
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An equipment grounding conductor, as described in 250.118, shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s). Exception No. 1: For installations made in compliance with previous editions of this Code that permitted such connection, the grounded conductor run with the supply to the building or structure shall be permitted to serve as the ground-fault return path if all of the following requirements continue to be met: (1) An equipment grounding conductor is not run with the supply to the building or structure. (2) There are no continuous metallic paths bonded to the grounding system in each building or structure involved. (3) Ground-fault protection of equipment has not been installed on the supply side of the feeder(s). If the grounded conductor is used for grounding in accordance with the provision of this exception, the size of the grounded conductor shall not be smaller than the larger of either of the following: (1) The calculated neutral load in accordance with 220.61 (2) The minimum equipment grounding conductor sized in accordance with 250.122 Exception No. 2: If system bonding jumpers are installed in accordance with 250.30(A)(1), Exception No. 2, the feeder grounded circuit conductor at the building or structure served shall be connected to the equipment grounding conductors, grounding electrode conductor, and the enclosure for the first disconnecting means. [250.32(B)(1)](https://2023.antflix.net#250.32(B)(1))
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https://2023.antflix.net#250.32(B)(1)
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Chapter 2 Wiring and Protection
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250.32(B)(2)
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With Overcurrent Protection. If overcurrent protection is provided where the conductors originate, the installation shall comply with 250.32(B)(1).Without Overcurrent Protection. If overcurrent protection is not provided where the conductors originate, the installation shall comply with 250.30(A). If installed, the supply-side bonding jumper shall be connected to the building or structure disconnecting means and to the grounding electrode(s). [250.32(B)(2)](https://2023.antflix.net#250.32(B)(2))
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https://2023.antflix.net#250.32(B)(2)
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Chapter 2 Wiring and Protection
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250.32(C)(1)
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An equipment grounding conductor, as described in 250.118, shall be installed with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The grounding electrode(s) shall also be connected to the building or structure disconnecting means. [250.32(C)(1)](https://2023.antflix.net#250.32(C)(1))
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https://2023.antflix.net#250.32(C)(1)
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Chapter 2 Wiring and Protection
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250.32(C)(2)
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With Overcurrent Protection. If overcurrent protection is provided where the conductors originate, the installation shall comply with 250.32(C)(1).Without Overcurrent Protection. If overcurrent protection is not provided where the conductors originate, the installation shall comply with 250.30(B). If installed, the supply-side bonding jumper shall be connected to the building or structure disconnecting means and to the grounding electrode(s). [250.32(C)(2)](https://2023.antflix.net#250.32(C)(2))
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https://2023.antflix.net#250.32(C)(2)
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Chapter 2 Wiring and Protection
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250.32(D)
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If one or more disconnecting means supply one or more additional buildings or structures under single management, and where these disconnecting means are located remote from those buildings or structures in accordance with 225.31(B), Exception No. 1 and No. 2, 700.12(D)(4), 701.12(D)(3), or 702.12, all of the following conditions shall be met: The connection of the grounded conductor to the grounding electrode, to normally non-current-carrying metal parts of equipment, or to the equipment grounding conductor at a separate building or structure shall not be made.An equipment grounding conductor for grounding and bonding any normally non-current-carrying metal parts of equipment, interior metal piping systems, and building or structural metal frames is run with the circuit conductors to a separate building or structure and connected to existing grounding electrode(s) required in Part III of this article, or, if there are no existing electrodes, the grounding electrode(s) required in Part III of this article shall be installed if a separate building or structure is supplied by more than one branch circuit.The connection between the equipment grounding conductor and the grounding electrode at a separate building or structure shall be made in a junction box, panelboard, or similar enclosure located immediately inside or outside the separate building or structure. [250.32(D)](https://2023.antflix.net#250.32(D))
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https://2023.antflix.net#250.32(D)
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Chapter 2 Wiring and Protection
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250.32(E)
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The size of the grounding electrode conductor to the grounding electrode(s) shall not be smaller than given in 250.66, based on the largest ungrounded supply conductor. The installation shall comply with Part III of this article. [250.32(E)](https://2023.antflix.net#250.32(E))
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https://2023.antflix.net#250.32(E)
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Chapter 2 Wiring and Protection
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250.34(A)
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The frame of a portable generator shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by the generator under both of the following conditions: The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both.The normally non-current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are connected to the generator frame. [250.34(A)](https://2023.antflix.net#250.34(A))
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https://2023.antflix.net#250.34(A)
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Chapter 2 Wiring and Protection
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250.34(B)
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The frame of a vehicle or trailer shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by a generator located on this vehicle or trailer under all of the following conditions: The frame of the generator is bonded to the vehicle or trailer frame.The generator supplies only equipment located on the vehicle or trailer; cord-and-plug-connected equipment through receptacles mounted on the vehicle; or both equipment located on the vehicle or trailer and cord-and-plug-connected equipment through receptacles mounted on the vehicle, trailer, or on the generator.The normally non-current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are connected to the generator frame. [250.34(B)](https://2023.antflix.net#250.34(B))
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https://2023.antflix.net#250.34(B)
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Chapter 2 Wiring and Protection
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250.34(C)
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A conductor that is required to be grounded by 250.26 shall be connected to the generator frame if the generator is a component of a separately derived system. Informational Note: See 250.30 for grounding portable generators supplying fixed wiring systems. [250.34(C)](https://2023.antflix.net#250.34(C))
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https://2023.antflix.net#250.34(C)
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Chapter 2 Wiring and Protection
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250.35
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A conductor that provides an effective ground-fault current path shall be installed with the supply conductors from a permanently installed generator(s) to the first disconnecting mean(s) in accordance with 250.35(A) or (B). [250.35](https://2023.antflix.net#250.35)
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https://2023.antflix.net#250.35
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Chapter 2 Wiring and Protection
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250.35(A)
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If the generator is installed as a separately derived system, the requirements in 250.30 shall apply. [250.35(A)](https://2023.antflix.net#250.35(A))
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https://2023.antflix.net#250.35(A)
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Chapter 2 Wiring and Protection
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250.35(B)
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If the generator is installed as a nonseparately derived system, and overcurrent protection is not integral with the generator assembly, a supply-side bonding jumper shall be installed between the generator equipment grounding terminal and the equipment grounding terminal, bar, or bus of the disconnecting mean(s). It shall be sized in accordance with 250.102(C) based on the size of the conductors supplied by the generator. [250.35(B)](https://2023.antflix.net#250.35(B))
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https://2023.antflix.net#250.35(B)
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Chapter 2 Wiring and Protection
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250.36
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Impedance grounded systems in which a grounding impedance device, typically a resistor, limits the ground-fault current shall be permitted for 3-phase ac systems of 480 volts to 1000 volts if all the following conditions are met: The conditions of maintenance and supervision ensure that only qualified persons service the installation.Ground detectors are installed on the system.Line-to-neutral loads are not served.Impedance grounded systems shall comply with 250.36(A) through (G).Informational Note: See NFPA 70E-2021, Standard for Electrical Safety in the Workplace, Annex O, for information on impedance grounding to reduce arc-flash hazards. [250.36](https://2023.antflix.net#250.36)
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https://2023.antflix.net#250.36
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Chapter 2 Wiring and Protection
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250.36(A)
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The grounding impedance device shall be installed between the grounding electrode conductor and the impedance grounding conductor connected to the system neutral point. If a neutral point is not available, the grounding impedance shall be installed between the grounding electrode conductor and the impedance grounding conductor connected to the neutral point derived from a grounding transformer. [250.36(A)](https://2023.antflix.net#250.36(A))
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https://2023.antflix.net#250.36(A)
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Chapter 2 Wiring and Protection
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250.36(B)
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The impedance grounding conductor from the neutral point of the transformer or generator to its connection point to the grounding impedance shall be fully insulated. The impedance grounding conductor shall have an ampacity of not less than the maximum current rating of the grounding impedance but in no case shall the impedance grounding conductor be smaller than 8 AWG copper or 6 AWG aluminum or copper-clad aluminum. [250.36(B)](https://2023.antflix.net#250.36(B))
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https://2023.antflix.net#250.36(B)
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Chapter 2 Wiring and Protection
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250.36(C)
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The system shall not be connected to ground except through the grounding impedance device. Informational Note: The impedance is normally selected to limit the ground-fault current to a value slightly greater than or equal to the capacitive charging current of the system. This value of impedance will also limit transient overvoltages to safe values. For guidance, refer to criteria for limiting transient overvoltages in IEEE 3003.1-2019, Recommended Practice for System Grounding of Industrial and Commercial Power Systems. [250.36(C)](https://2023.antflix.net#250.36(C))
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https://2023.antflix.net#250.36(C)
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Chapter 2 Wiring and Protection
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250.36(D)
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The impedance grounding conductor shall be permitted to be installed in a separate raceway from the ungrounded conductors. It shall not be required to run this conductor with the phase conductors to the first system disconnecting means or overcurrent device. [250.36(D)](https://2023.antflix.net#250.36(D))
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https://2023.antflix.net#250.36(D)
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Chapter 2 Wiring and Protection
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250.36(E)
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The impedance bonding jumper (the connection between the equipment grounding conductors and the grounding impedance device) shall be an unspliced conductor run from the first system disconnecting means or overcurrent device to the grounded side of the grounding impedance device. [250.36(E)](https://2023.antflix.net#250.36(E))
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https://2023.antflix.net#250.36(E)
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Chapter 2 Wiring and Protection
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250.36(F)
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For services or separately derived systems, the grounding electrode conductor shall be connected at any point from the grounded side of the grounding impedance device to the equipment grounding connection at the service equipment or the first system disconnecting means of a separately derived system. [250.36(F)](https://2023.antflix.net#250.36(F))
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https://2023.antflix.net#250.36(F)
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Chapter 2 Wiring and Protection
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250.36(G)
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The impedance bonding jumper shall be sized in accordance with either of the following: If the grounding electrode conductor connection is made at the grounding impedance device, the equipment bonding jumper shall be sized in accordance with 250.66, based on the size of the service entrance conductors for a service or the derived phase conductors for a separately derived system.If the grounding electrode conductor is connected at the first system disconnecting means or overcurrent device, the impedance bonding jumper shall be sized the same as the impedance grounding conductor in 250.36(B). [250.36(G)](https://2023.antflix.net#250.36(G))
|
https://2023.antflix.net#250.36(G)
|
Chapter 2 Wiring and Protection
|
250.50
|
All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. If none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used. Exception: Concrete-encased electrodes of existing buildings or structures shall not be required to be part of the grounding electrode system if the rebar is not accessible for use without disturbing the concrete. [250.50](https://2023.antflix.net#250.50)
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https://2023.antflix.net#250.50
|
Chapter 2 Wiring and Protection
|
250.52(A)(1)
|
A metal underground water pipe in direct contact with the earth for 3.0 m (10 ft) or more (including any metal well casing bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductor(s) or jumper(s), if installed. [250.52(A)(1)](https://2023.antflix.net#250.52(A)(1))
|
https://2023.antflix.net#250.52(A)(1)
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Chapter 2 Wiring and Protection
|
250.52(A)(2)
|
One or more metal in-ground support structure(s) in direct contact with the earth vertically for 3.0 m (10 ft) or more, with or without concrete encasement. If multiple metal in-ground support structures are present at a building or a structure, it shall be permissible to bond only one into the grounding electrode system. Informational Note: Metal in-ground support structures include, but are not limited to, pilings, casings, and other structural metal. [250.52(A)(2)](https://2023.antflix.net#250.52(A)(2))
|
https://2023.antflix.net#250.52(A)(2)
|
Chapter 2 Wiring and Protection
|
250.52(A)(3)
|
A concrete-encased electrode shall consist of at least 6.0 m (20 ft) of either of the following: One or more bare or zinc galvanized or other electrically conductive coated rebar of not less than 13 mm (1/2 in.) in diameter, installed in one continuous 6.0 m (20 ft) length, or if in multiple pieces, the rebar shall be connected together by steel tie wires, exothermic welding, welding, or other effective means to create a 6.0 m (20 ft) or greater lengthBare copper conductor not smaller than 4 AWGMetal components shall be encased by at least 50 mm (2 in.) of concrete and shall be located horizontally within that portion of a concrete foundation or footing that is in direct contact with the earth or within vertical foundations or structural components or members that are in direct contact with the earth. If multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.Informational Note: Concrete installed with insulation, vapor barriers, films, or similar items separating the concrete from the earth is not considered to be in "direct contact" with the earth. [250.52(A)(3)](https://2023.antflix.net#250.52(A)(3))
|
https://2023.antflix.net#250.52(A)(3)
|
Chapter 2 Wiring and Protection
|
250.52(A)(4)
|
A ground ring encircling the building or structure, in direct contact with the earth, consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 2 AWG. [250.52(A)(4)](https://2023.antflix.net#250.52(A)(4))
|
https://2023.antflix.net#250.52(A)(4)
|
Chapter 2 Wiring and Protection
|
250.52(A)(5)
|
Rod and pipe electrodes shall not be less than 2.44 m (8 ft) in length and consist of the following materials. Grounding electrodes of pipe or conduit shall not be smaller than metric designator 21 (trade size 3/4) and, where of steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.Rod-type grounding electrodes of stainless steel and copper or zinc-coated steel shall be at least 15.87 mm (5/8 in.) in diameter, unless listed. [250.52(A)(5)](https://2023.antflix.net#250.52(A)(5))
|
https://2023.antflix.net#250.52(A)(5)
|
Chapter 2 Wiring and Protection
|
250.52(A)(6)
|
Other listed grounding electrodes shall be permitted. [250.52(A)(6)](https://2023.antflix.net#250.52(A)(6))
|
https://2023.antflix.net#250.52(A)(6)
|
Chapter 2 Wiring and Protection
|
250.52(A)(7)
|
Each plate electrode shall expose not less than 0.186 m2 (2 ft2) of surface to exterior soil. Electrodes of bare or electrically conductive coated iron or steel plates shall be at least 6.4 mm (1/4 in.) in thickness. Solid, uncoated electrodes of nonferrous metal shall be at least 1.5 mm (0.06 in.) in thickness. [250.52(A)(7)](https://2023.antflix.net#250.52(A)(7))
|
https://2023.antflix.net#250.52(A)(7)
|
Chapter 2 Wiring and Protection
|
250.52(A)(8)
|
Other local metal underground systems or structures such as piping systems, underground tanks, and underground metal well casings that are not bonded to a metal water pipe. [250.52(A)(8)](https://2023.antflix.net#250.52(A)(8))
|
https://2023.antflix.net#250.52(A)(8)
|
Chapter 2 Wiring and Protection
|
250.52(B)
|
The following systems and materials shall not be used as grounding electrodes: Metal underground gas piping systemsAluminumThe structures and structural rebar described in 680.26(B)(1) and (B)(2)Informational Note: See 250.104(B) for bonding requirements of gas piping. [250.52(B)](https://2023.antflix.net#250.52(B))
|
https://2023.antflix.net#250.52(B)
|
Chapter 2 Wiring and Protection
|
250.53(A)
|
Rod, pipe, and plate electrodes shall be free from nonconductive coatings such as paint or enamel. Rod, pipe, and plate electrodes shall meet the requirements of 250.53(A)(1) through (A)(3). [250.53(A)](https://2023.antflix.net#250.53(A))
|
https://2023.antflix.net#250.53(A)
|
Chapter 2 Wiring and Protection
|
250.53(A)(1)
|
If practicable, rod, pipe, and plate electrodes shall be embedded below permanent moisture level. [250.53(A)(1)](https://2023.antflix.net#250.53(A)(1))
|
https://2023.antflix.net#250.53(A)(1)
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Chapter 2 Wiring and Protection
|
250.53(A)(2)
|
A single rod, pipe, or plate electrode shall be supplemented by an additional electrode of a type specified in 250.52(A)(2) through (A)(8). The supplemental electrode shall be permitted to be bonded to one of the following: Rod, pipe, or plate electrodeGrounding electrode conductorGrounded service-entrance conductorNonflexible grounded service racewayAny grounded service enclosureException: If a single rod, pipe, or plate grounding electrode has a resistance to earth of 25 ohms or less, the supplemental electrode shall not be required. [250.53(A)(2)](https://2023.antflix.net#250.53(A)(2))
|
https://2023.antflix.net#250.53(A)(2)
|
Chapter 2 Wiring and Protection
|
250.53(A)(3)
|
If multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart. Informational Note: The paralleling efficiency of rods is increased by spacing them twice the length of the longest rod. [250.53(A)(3)](https://2023.antflix.net#250.53(A)(3))
|
https://2023.antflix.net#250.53(A)(3)
|
Chapter 2 Wiring and Protection
|
250.53(A)(4)
|
The electrode shall be installed such that at least 2.44 m (8 ft) of length is in contact with the soil. It shall be driven to a depth of not less than 2.44 m (8 ft) except that, where rock bottom is encountered, the electrode shall be driven at an oblique angle not to exceed 45 degrees from the vertical or, where rock bottom is encountered at an angle up to 45 degrees, the electrode shall be permitted to be buried in a trench that is at least 750 mm (30 in.) deep. The upper end of the electrode shall be flush with or below ground level unless the aboveground end and the grounding electrode conductor attachment are protected against physical damage as specified in 250.10. [250.53(A)(4)](https://2023.antflix.net#250.53(A)(4))
|
https://2023.antflix.net#250.53(A)(4)
|
Chapter 2 Wiring and Protection
|
250.53(A)(5)
|
Plate electrodes shall be installed not less than 750 mm (30 in.) below the surface of the earth. [250.53(A)(5)](https://2023.antflix.net#250.53(A)(5))
|
https://2023.antflix.net#250.53(A)(5)
|
Chapter 2 Wiring and Protection
|
250.53(B)
|
If more than one of the electrodes of the type specified in 250.52(A)(5) or (A)(7) are used, each electrode of one grounding system (including that used for strike termination devices) shall not be less than 1.83 m (6 ft) from any other electrode of another grounding system. [250.53(B)](https://2023.antflix.net#250.53(B))
|
https://2023.antflix.net#250.53(B)
|
Chapter 2 Wiring and Protection
|
250.53(C)
|
The bonding jumper(s) used to connect the grounding electrodes together to form the grounding electrode system shall be installed in accordance with 250.64(A), (B), and (E), shall be sized in accordance with 250.66, and shall be connected in the manner specified in 250.70. Rebar shall not be used as a conductor to interconnect the electrodes of grounding electrode systems. [250.53(C)](https://2023.antflix.net#250.53(C))
|
https://2023.antflix.net#250.53(C)
|
Chapter 2 Wiring and Protection
|
250.53(D)
|
If used as a grounding electrode, metal underground water pipe shall meet the requirements of 250.53(D)(1) and (D)(2). [250.53(D)](https://2023.antflix.net#250.53(D))
|
https://2023.antflix.net#250.53(D)
|
Chapter 2 Wiring and Protection
|
250.53(D)(1)
|
Continuity of the grounding path or the bonding connection to interior piping shall not rely on water meters or filtering devices and similar equipment. [250.53(D)(1)](https://2023.antflix.net#250.53(D)(1))
|
https://2023.antflix.net#250.53(D)(1)
|
Chapter 2 Wiring and Protection
|
250.53(D)(2)
|
A metal underground water pipe shall be supplemented by an additional electrode of a type specified in 250.52(A)(2) through (A)(8). If the supplemental electrode is of the rod, pipe, or plate type, it shall comply with 250.53(A). The supplemental electrode shall be bonded to one of the following: Grounding electrode conductorGrounded service-entrance conductorNonflexible grounded service racewayAny grounded service enclosureAs provided by 250.32(B)Exception: The supplemental electrode shall be permitted to be bonded to the interior metal water piping as specified in 250.68(C)(1). [250.53(D)(2)](https://2023.antflix.net#250.53(D)(2))
|
https://2023.antflix.net#250.53(D)(2)
|
Chapter 2 Wiring and Protection
|
250.53(E)
|
If the supplemental electrode is a rod, pipe, or plate electrode, that portion of the bonding jumper that is the sole connection to the supplemental grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum or copper-clad aluminum wire. [250.53(E)](https://2023.antflix.net#250.53(E))
|
https://2023.antflix.net#250.53(E)
|
Chapter 2 Wiring and Protection
|
250.53(F)
|
The ground ring shall be installed not less than 750 mm (30 in.) below the surface of the earth. [250.53(F)](https://2023.antflix.net#250.53(F))
|
https://2023.antflix.net#250.53(F)
|
Chapter 2 Wiring and Protection
|
250.54
|
One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and (B)(4). [250.54](https://2023.antflix.net#250.54)
|
https://2023.antflix.net#250.54
|
Chapter 2 Wiring and Protection
|
250.58
|
If an ac system is connected to a grounding electrode in or at a building or structure, the same electrode shall be used to ground conductor enclosures and equipment in or on that building or structure. If separate services, feeders, or branch circuits supply a building and are required to be connected to a grounding electrode(s) the same grounding electrode(s) shall be used. [250.58](https://2023.antflix.net#250.58)
|
https://2023.antflix.net#250.58
|
Chapter 2 Wiring and Protection
|
250.60
|
Conductors and driven pipes, rods, or plate electrodes used for grounding strike termination devices shall not be used in lieu of the grounding electrodes required by 250.50 for grounding wiring systems and equipment. This provision shall not prohibit the required bonding together of grounding electrodes of different systems. Informational Note No. 1: See 250.106 for the bonding requirement of the lightning protection system components to the building or structure grounding electrode system. Informational Note No. 2: Bonding together of all separate grounding electrodes will limit voltage differences between them and between their associated wiring systems. [250.60](https://2023.antflix.net#250.60)
|
https://2023.antflix.net#250.60
|
Chapter 2 Wiring and Protection
|
250.62
|
The grounding electrode conductor shall be of copper, aluminum, copper-clad aluminum, or the items as permitted in 250.68(C). The material selected shall be resistant to any corrosive condition existing at the installation or shall be protected against corrosion. Conductors of the wire type shall be solid or stranded, insulated, covered, or bare. [250.62](https://2023.antflix.net#250.62)
|
https://2023.antflix.net#250.62
|
Chapter 2 Wiring and Protection
|
250.64
|
Grounding electrode conductors at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system shall be installed as specified in 250.64(A) through (G). [250.64](https://2023.antflix.net#250.64)
|
https://2023.antflix.net#250.64
|
Chapter 2 Wiring and Protection
|
250.64(A)
|
Grounding electrode conductors of bare, covered, or insulated aluminum or copper-clad aluminum shall comply with the following: Bare or covered conductors without an extruded polymeric covering shall not be installed where subject to corrosive conditions or be installed in direct contact with concrete.Terminations made within outdoor enclosures that are listed and identified for the environment shall be permitted within 450 mm (18 in.) of the bottom of the enclosure.Aluminum or copper-clad aluminum conductors external to buildings or equipment enclosures shall not be terminated within 450 mm (18 in.) of the earth. [250.64(A)](https://2023.antflix.net#250.64(A))
|
https://2023.antflix.net#250.64(A)
|
Chapter 2 Wiring and Protection
|
250.64(B)
|
If exposed, a grounding electrode conductor or its enclosure shall be securely fastened to the surface on which it is carried. Grounding electrode conductors shall be permitted to be installed on or through framing members. [250.64(B)](https://2023.antflix.net#250.64(B))
|
https://2023.antflix.net#250.64(B)
|
Chapter 2 Wiring and Protection
|
250.64(B)(1)
|
A 6 AWG or larger copper, copper-clad aluminum, or aluminum grounding electrode conductor not exposed to physical damage shall be permitted to be run along the surface of the building construction without metal covering or protection. [250.64(B)(1)](https://2023.antflix.net#250.64(B)(1))
|
https://2023.antflix.net#250.64(B)(1)
|
Chapter 2 Wiring and Protection
|
250.64(B)(2)
|
A 6 AWG or larger copper, copper-clad aluminum, or aluminum grounding electrode conductor exposed to physical damage shall be protected in rigid metal conduit (RMC), intermediate metal conduit (IMG), Schedule 80 rigid polyvinyl chloride conduit (PVC), reinforced thermosetting resin conduit Type XW (RTRC-XW), electrical metallic tubing (EMT), or cable armor. [250.64(B)(2)](https://2023.antflix.net#250.64(B)(2))
|
https://2023.antflix.net#250.64(B)(2)
|
Chapter 2 Wiring and Protection
|
250.64(B)(3)
|
Grounding electrode conductors smaller than 6 AWG shall be protected in RMC, IMC, Schedule 80 PVC, RTRC-XW, EMT, or cable armor. [250.64(B)(3)](https://2023.antflix.net#250.64(B)(3))
|
https://2023.antflix.net#250.64(B)(3)
|
Chapter 2 Wiring and Protection
|
250.64(B)(4)
|
Grounding electrode conductors and grounding electrode bonding jumpers in contact with the earth shall not be required to comply with 300.5 or 305.15, but shall be buried or otherwise protected if subject to physical damage. [250.64(B)(4)](https://2023.antflix.net#250.64(B)(4))
|
https://2023.antflix.net#250.64(B)(4)
|
Chapter 2 Wiring and Protection
|
250.64(C)
|
Except as provided in 250.30(A)(5) and (A)(6), 250.30(B)(1), and 250.68(C), grounding electrode conductor(s) shall be installed in one continuous length without a splice or joint. If necessary, splices or connections shall be made as permitted in the following: Splicing of the wire-type grounding electrode conductor shall be permitted only by irreversible compression-type connectors listed as grounding and bonding equipment or by the exothermic welding process.Sections of busbars shall be permitted to be connected together to form a grounding electrode conductor.Bolted, riveted, or welded connections of structural metal frames of buildings or structures.Threaded, welded, brazed, soldered or bolted-flange connections of metal water piping. [250.64(C)](https://2023.antflix.net#250.64(C))
|
https://2023.antflix.net#250.64(C)
|
Chapter 2 Wiring and Protection
|
250.64(D)
|
If a building or structure is supplied by a service or feeder with two or more disconnecting means in separate enclosures, the grounding electrode connections shall be made in accordance with 250.64(D)(1), (D)(2), or (D)(3). [250.64(D)](https://2023.antflix.net#250.64(D))
|
https://2023.antflix.net#250.64(D)
|
Chapter 2 Wiring and Protection
|
250.64(D)(1)
|
A common grounding electrode conductor and grounding electrode conductor taps shall be installed. The common grounding electrode conductor shall be sized in accordance with 250.66, based on the sum of the circular mil area of the largest ungrounded conductor(s) of each set of conductors that supplies the disconnecting means. If the service-entrance conductors connect directly to the overhead service conductors, service drop, underground service conductors, or service lateral, the common grounding electrode conductor shall be sized in accordance with Table 250.66, note 1. A grounding electrode conductor tap shall extend to the inside of each disconnecting means enclosure. The grounding electrode conductor taps shall be sized in accordance with 250.66 for the largest service-entrance or feeder conductor serving the individual enclosure. The tap conductors shall be connected to the common grounding electrode conductor by one of the following methods in such a manner that the common grounding electrode conductor remains without a splice or joint:Exothermic welding.Connectors listed as grounding and bonding equipment.Connections to an aluminum or copper busbar not less than 6 mm thick × 50 mm wide (1/4 in. thick × 2 in. wide) and of a length to accommodate the number of terminations necessary for the installation. The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed connector or by the exothermic welding process. If aluminum busbars are used, the installation shall comply with 250.64(A). [250.64(D)(1)](https://2023.antflix.net#250.64(D)(1))
|
https://2023.antflix.net#250.64(D)(1)
|
Chapter 2 Wiring and Protection
|
250.64(D)(2)
|
A grounding electrode conductor shall be connected between the grounding electrode system and one or more of the following, as applicable: Grounded conductor in each service equipment disconnecting means enclosureEquipment grounding conductor installed with the feeder(s) or branch circuit(s) for other than servicesSupply-side bonding jumperEach grounding electrode conductor shall be sized in accordance with 250.66 based on the service-entrance or feeder conductor(s) supplying the individual disconnecting means. [250.64(D)(2)](https://2023.antflix.net#250.64(D)(2))
|
https://2023.antflix.net#250.64(D)(2)
|
Chapter 2 Wiring and Protection
|
250.64(D)(3)
|
A grounding electrode conductor shall be connected in a wireway or other accessible enclosure on the supply side of the disconnecting means to one or more of the following, as applicable: Grounded service conductor(s)Equipment grounding conductor installed with the feederSupply-side bonding jumperThe connection shall be made with exothermic welding or a connector listed as grounding and bonding equipment. The grounding electrode conductor shall be sized in accordance with 250.66 based on the service-entrance or feeder conductor(s) at the common location where the connection is made. [250.64(D)(3)](https://2023.antflix.net#250.64(D)(3))
|
https://2023.antflix.net#250.64(D)(3)
|
Chapter 2 Wiring and Protection
|
250.64(E)(1)
|
Ferrous metal raceways, enclosures, and cable armor for grounding electrode conductors shall be electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode and shall be securely fastened to the ground clamp or fitting. Ferrous metal raceways, enclosures, and cable armor shall be bonded at each end of the raceway or enclosure to the grounding electrode or grounding electrode conductor to create an electrically parallel path. Nonferrous metal raceways, enclosures, and cable armor shall not be required to be electrically continuous. [250.64(E)(1)](https://2023.antflix.net#250.64(E)(1))
|
https://2023.antflix.net#250.64(E)(1)
|
Chapter 2 Wiring and Protection
|
250.64(E)(2)
|
Bonding shall be in compliance with 250.92(B) and ensured by one of the methods in 250.92(B)(2) through (B)(4). [250.64(E)(2)](https://2023.antflix.net#250.64(E)(2))
|
https://2023.antflix.net#250.64(E)(2)
|
Chapter 2 Wiring and Protection
|
250.64(E)(3)
|
The bonding jumper for a grounding electrode conductor(s), raceway(s), enclosure(s), or cable armor shall be the same size as, or larger than, the largest enclosed grounding electrode conductor. [250.64(E)(3)](https://2023.antflix.net#250.64(E)(3))
|
https://2023.antflix.net#250.64(E)(3)
|
Chapter 2 Wiring and Protection
|
250.64(E)(4)
|
If a raceway is used as protection for a grounding electrode conductor, the installation shall comply with the requirements of the applicable raceway article. [250.64(E)(4)](https://2023.antflix.net#250.64(E)(4))
|
https://2023.antflix.net#250.64(E)(4)
|
Chapter 2 Wiring and Protection
|
250.64(F)
|
Grounding electrode conductor(s) and bonding jumpers interconnecting grounding electrodes shall be installed in accordance with one of the following. The grounding electrode conductor shall be sized for the largest grounding electrode conductor required among all the electrodes connected to it. The grounding electrode conductor shall be permitted to be run to any convenient grounding electrode available in the grounding electrode system where the other electrode(s), if any, is connected by bonding jumpers that are installed in accordance with 250.53(C).Grounding electrode conductor(s) shall be permitted to be run to one or more grounding electrode(s) individually.Bonding jumper(s) from grounding electrode(s) shall be permitted to be connected to an aluminum or copper busbar not less than 6 mm thick × 50 mm wide (1/4 in. thick × 2 in wide.) and of sufficient length to accommodate the number of terminations necessary for the installation. The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed connector or by the exothermic welding process. The grounding electrode conductor shall be permitted to be run to the busbar. Where aluminum busbars are used, the installation shall comply with 250.64(A). [250.64(F)](https://2023.antflix.net#250.64(F))
|
https://2023.antflix.net#250.64(F)
|
Chapter 2 Wiring and Protection
|
250.64(G)
|
Grounding electrode conductors shall not be installed through a ventilation opening of an enclosure. [250.64(G)](https://2023.antflix.net#250.64(G))
|
https://2023.antflix.net#250.64(G)
|
Chapter 2 Wiring and Protection
|
250.66
|
The size of the grounding electrode conductor and bonding jumper(s) for connection of grounding electrodes shall not be smaller than given in Table 250.66, except as permitted in 250.66(A) through (C).Table 250.66 Grounding Electrode Conductor for Alternating-Current Systems Size of Largest Ungrounded Conductor or Equivalent Area for Parallel Conductors (AWG/kcmil) Size of Grounding Electrode Conductor (AWG/kcmil) Copper Aluminum or Copper-Clad Aluminum Copper Aluminum or Copper-Clad Aluminum 2 or smaller 1/0 or smaller 8 6 1 or 1/0 2/0 or 3/0 6 4 2/0 or 3/0 4/0 or 250 4 2 Over 3/0 through 350 Over 250 through 500 2 1/0 Over 350 through 600 Over 500 through 900 1/0 3/0 Over 600 through 1100 Over 900 through 1750 2/0 4/0 Over 1100 Over 1750 3/0 250 Notes:If multiple sets of service-entrance conductors connect directly to a service drop, set of overhead service conductors, set of underground service conductors, or service lateral, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.If there are no service-entrance conductors, the grounding electrode conductor size shall be determined by the equivalent size of the largest service-entrance conductor required for the load to be served.See installation restrictions in 250.64. [250.66](https://2023.antflix.net#250.66)
|
https://2023.antflix.net#250.66
|
Chapter 2 Wiring and Protection
|
250.66(A)
|
If the grounding electrode conductor or bonding jumper connected to a single or multiple rod, pipe, or plate electrode(s), or any combination thereof, as described in 250.52(A)(5) or (A)(7), does not extend on to other types of electrodes that require a larger size conductor, the grounding electrode conductor shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum or copper-clad aluminum wire. [250.66(A)](https://2023.antflix.net#250.66(A))
|
https://2023.antflix.net#250.66(A)
|
Chapter 2 Wiring and Protection
|
250.66(B)
|
If the grounding electrode conductor or bonding jumper connected to a single or multiple concrete-encased electrode(s), as described in 250.52(A)(3), does not extend on to other types of electrodes that require a larger size of conductor, the grounding electrode conductor shall not be required to be larger than 4 AWG copper wire. [250.66(B)](https://2023.antflix.net#250.66(B))
|
https://2023.antflix.net#250.66(B)
|
Chapter 2 Wiring and Protection
|
250.66(C)
|
If the grounding electrode conductor or bonding jumper connected to a ground ring, as described in 250.52(A)(4), does not extend on to other types of electrodes that require a larger size of conductor, the grounding electrode conductor shall not be required to be larger than the conductor used for the ground ring. [250.66(C)](https://2023.antflix.net#250.66(C))
|
https://2023.antflix.net#250.66(C)
|
Chapter 2 Wiring and Protection
|
250.68
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The connection of a grounding electrode conductor at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system and associated bonding jumper(s) shall be made as specified 250.68(A) through (C). [250.68](https://2023.antflix.net#250.68)
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https://2023.antflix.net#250.68
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Chapter 2 Wiring and Protection
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250.68(A)
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All mechanical elements used to terminate a grounding electrode conductor or bonding jumper to a grounding electrode shall be accessible. Exception No. 1: An encased or buried connection to a concrete-encased, driven, or buried grounding electrode shall not be required to be accessible. Exception No. 2: Exothermic or irreversible compression connections used at terminations, together with the mechanical means used to attach such terminations to fireproofed structural metal whether or not the mechanical means is reversible, shall not be required to be accessible. [250.68(A)](https://2023.antflix.net#250.68(A))
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https://2023.antflix.net#250.68(A)
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Chapter 2 Wiring and Protection
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250.68(B)
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The connection of a grounding electrode conductor or bonding jumper to a grounding electrode shall be made in a manner that will ensure an effective grounding path. Where necessary to ensure the grounding path for a metal piping system used as a grounding electrode, bonding shall be provided around insulated joints and around any equipment likely to be disconnected for repairs or replacement. Bonding jumpers shall be of sufficient length to permit removal of such equipment while retaining the integrity of the grounding path. [250.68(B)](https://2023.antflix.net#250.68(B))
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https://2023.antflix.net#250.68(B)
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Chapter 2 Wiring and Protection
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250.68(C)
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Grounding electrode conductors and bonding jumpers shall be permitted to be connected at the following locations and used to extend the connection to an electrode(s): Interior metal water piping that is electrically continuous with a metal underground water pipe electrode and is located not more than 1.52 m (5 ft) from the point of entrance to the building, as measured along the water piping, shall be permitted to extend the connection to an electrode(s). Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building, as measured along the water piping, shall not be used as a conductor to interconnect electrodes of the grounding electrode system.Exception: In industrial, commercial, and institutional buildings or structures, if conditions of maintenance and supervision ensure that only qualified persons service the installation, interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building, as measured along the water piping, shall be permitted as a bonding conductor to interconnect electrodes that are part of the grounding electrode system, or as a grounding electrode conductor, if the entire length, other than short sections passing perpendicularly through walls, floors, or ceilings, of the interior metal water pipe that is being used for the conductor is exposed.The metal structural frame of a building shall be permitted to be used as a conductor to interconnect electrodes that are part of the grounding electrode system, or as a grounding electrode conductor. Hold-down bolts securing the structural steel column that are connected to a concrete-encased electrode complying with 250.52(A)(3) and located in the support footing or foundation shall be permitted to connect the metal structural frame of a building or structure to the concrete-encased grounding electrode. The hold-down bolts shall be connected to the concrete-encased electrode by welding, exothermic welding, steel tie wires, or other approved means.A rebar-type concrete-encased electrode installed in accordance with 250.52(A)(3) with an additional rebar section extended from its location within the concrete foundation or footing to an accessible location that is not subject to corrosion shall be permitted for connection of grounding electrode conductors and bonding jumpers in accordance with the following:The additional rebar section shall be continuous with the grounding electrode rebar or shall be connected to the grounding electrode rebar and connected together by steel tie wires, exothermic welding, welding, or other effective means.The rebar extension shall not be exposed to contact with the earth without corrosion protection.Rebar shall not be used as a conductor to interconnect the electrodes of grounding electrode systems. [250.68(C)](https://2023.antflix.net#250.68(C))
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https://2023.antflix.net#250.68(C)
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Chapter 2 Wiring and Protection
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250.70(A)
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The grounding or bonding conductor shall be connected to the grounding electrode by exothermic welding, listed lugs, listed pressure connectors, listed clamps, or other listed means. Connections depending on solder shall not be used. Ground clamps shall be listed for the materials of the grounding electrode and the grounding electrode conductor and, if used on pipe, rod, or other buried electrodes, shall also be listed for direct soil burial or concrete encasement. Not more than one conductor shall be connected to the grounding electrode by a single clamp or fitting unless the clamp or fitting is listed for multiple conductors. [250.70(A)](https://2023.antflix.net#250.70(A))
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https://2023.antflix.net#250.70(A)
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Chapter 2 Wiring and Protection
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250.70(B)
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For indoor communications purposes only, a listed sheet metal strap-type ground clamp having a rigid metal base that seats on the electrode and having a strap of such material and dimensions that it is not likely to stretch during or after installation shall be permitted. Informational Note: Listed ground clamps that are identified for direct burial are also suitable for concrete encasement. [250.70(B)](https://2023.antflix.net#250.70(B))
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https://2023.antflix.net#250.70(B)
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Chapter 2 Wiring and Protection
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250.80
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Metal enclosures and raceways for service conductors and equipment shall be connected to the grounded conductor if the electrical system is grounded or to the grounding electrode conductor for electrical systems that are not grounded. Exception: Metal components that are installed in a run of underground nonmetallic raceway(s) and are isolated from possible contact by a minimum cover of 450 mm (18 in.) to all parts of the metal components shall not be required to be connected to the grounded conductor, supply-side bonding jumper, or grounding electrode conductor. [250.80](https://2023.antflix.net#250.80)
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https://2023.antflix.net#250.80
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Chapter 2 Wiring and Protection
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250.84(A)
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The sheath or armor of a continuous underground metal-sheathed or armored service cable system that is connected to the grounded conductor on the supply side shall not be required to be connected to the grounded conductor at the building or structure. The sheath or armor shall be permitted to be insulated from the interior metal raceway or piping. [250.84(A)](https://2023.antflix.net#250.84(A))
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https://2023.antflix.net#250.84(A)
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Chapter 2 Wiring and Protection
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250.84(B)
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An underground metal service raceway that contains a metal-sheathed or armored cable connected to the grounded conductor shall not be required to be connected to the grounded conductor at the building or structure. The sheath or armor shall be permitted to be insulated from the interior metal raceway or piping. [250.84(B)](https://2023.antflix.net#250.84(B))
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https://2023.antflix.net#250.84(B)
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Chapter 2 Wiring and Protection
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250.86
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Except as permitted by 250.112(1), metal enclosures and raceways for other than service conductors shall be connected to the equipment grounding conductor. Exception No. 1: Metal enclosures and raceways for conductors added to existing installations of open wire, knob-and-tube wiring, and nonmetallic-sheathed cable shall not be required to be connected to the equipment grounding conductor if these enclosures or wiring methods comply with all the following: (1) Do not provide an equipment ground (2) Are in runs of less than 7.5 m (25 ft) (3) Are free from probable contact with ground, grounded metal, metal lath, or other conductive material (4) Are guarded against contact by persons Exception No. 2: Short sections of metal enclosures or raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be connected to the equipment grounding conductor. Exception No. 3: Metal components shall not be required to be connected to the equipment grounding conductor or supply-side bonding jumper if either of the following conditions exist: (1) The metal components are installed in a run of nonmetallic raceway(s) and isolated from possible contact by a minimum cover of 450 mm (18 in.) to any part of the metal components. (2) The metal components are part of an installation of nonmetallic raceway(s) and are isolated from possible contact to any part of the metal components by being encased in not less than 50 mm (2 in.) of concrete. [250.86](https://2023.antflix.net#250.86)
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https://2023.antflix.net#250.86
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Chapter 2 Wiring and Protection
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250.90
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Bonding shall be provided if necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed. [250.90](https://2023.antflix.net#250.90)
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https://2023.antflix.net#250.90
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Chapter 2 Wiring and Protection
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250.92(A)
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The normally noncurrent-carrying metal parts of equipment indicated in the following shall be bonded together: All raceways, cable trays, cablebus framework, auxiliary gutters, or service cable armor or sheath that enclose, contain, or support service conductors, except as permitted in 250.80All enclosures containing service conductors, including meter fittings, boxes, or the like, interposed in the service raceway or armor [250.92(A)](https://2023.antflix.net#250.92(A))
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https://2023.antflix.net#250.92(A)
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Chapter 2 Wiring and Protection
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250.92(B)
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Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s). Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one or more of the following methods:Bonding equipment to the grounded service conductor by an applicable method in 250.8(A)Connections made up wrenchtight using threaded couplings, threaded entries, or listed threaded hubs on enclosuresThreadless couplings and connectors if made up tight for metal raceways and metal-clad cablesOther listed devices, such as bonding-type locknuts, bushings, or bushings with bonding jumpers [250.92(B)](https://2023.antflix.net#250.92(B))
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https://2023.antflix.net#250.92(B)
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