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Grounding versus Bonding



250.53 Installation of Grounding Electrode System.

(A) Ground Rod Electrodes. Where practicable, ground rods must be embedded below permanent moisture level and must be free from nonconductive coatings such as paint or enamel [250.12].

Author's Comment: See 250.53(G) for additional details.
(B) Electrode Spacing. Where more than one grounding electrode system exists at a building or structure, they must be separated by at least 6 ft.

(C) Grounding Electrode Bonding Jumper. Where within 18 in. of earth, the conductor used to bond grounding electrodes together to form the grounding electrode system must be copper [250.64(A)], securely fastened to the surface on which it's carried, and be protected if exposed to physical damage [250.64(B)]. The bonding jumper to each electrode must be sized in accordance with 250.66.

In addition, the grounding electrode bonding jumpers must terminate to the grounding electrode by exothermic welding, listed lugs, listed pressure connectors, listed clamps, or other listed means [250.8]. When the termination is encased in concrete or buried, the termination fittings must be listed and identified for this purpose [250.70].

(D) Underground Metal Water Pipe Electrode.

(1) Continuity. The bonding connection to the interior metal water piping system, as required by 250.104(A), must not be dependent on water meters, filtering devices, or similar equipment likely to be disconnected for repairs or replacement. When necessary, a bonding jumper must be installed around insulated joints and equipment likely to be disconnected for repairs or replacement to assist in clearing and removing dangerous voltage on metal parts because of a ground fault. Figure 250.99

Author's Comment: See 250.68(B) and 250.104 for additional details.
(2) Underground Metal Water Pipe Supplemental Electrode Required. The underground metal water pipe grounding electrode, if present [250.52(A)(1)], must be supplemented by one of the following electrodes:
  • Metal frame of the building or structure [250.52(A)(2)]
  • Concrete-encased steel [250.52(A)(3)] Figure 250.100
  • Ground ring [250.52(A)(4)]
Where none of the above electrodes are available, one of the following electrodes must be used:
  • Ground rod in accordance with 250.56 [250.52(A)(5)]
  • Grounding plate [250.52(A)(6)]
  • Metal underground systems [250.52(A)(7)]
The underground water pipe supplemental electrode must terminate to one of the following:
  • Grounding electrode conductor
  • Grounded neutral service conductor
  • Metal service raceway
  • Service equipment enclosure Figure 250.101
(E) Underground Metal Water Pipe Supplemental Electrode Bonding Jumper. Where the supplemental electrode is a ground rod, that portion that is the sole connection to a ground rod isn't required to be larger than 6 AWG copper.

Author's Comment: The bonding jumper for the underground metal water pipe supplemental electrode is sized in accordance with 250.66, including Table 250.66, where applicable.
(F) Ground Ring. A ground ring encircling the building or structure, consisting of at least 20 ft of bare copper conductor not smaller than 2 AWG, must be buried at a depth of not less than 30 in. See 250.52(A)(4) for additional details.

(G) Ground Rod Electrodes. Ground rod electrodes must be installed so that not less than 8 ft of length is in contact with the soil. Where rock bottom is encountered, the ground rod must be driven at an angle not to exceed 45 degrees from vertical. If rock bottom is encountered at an angle up to 45 degrees from vertical, the ground rod can be buried in a minimum 30 in. deep trench. Figure 250.102

The upper end of the ground rod must be flush with or underground unless the grounding electrode conductor attachment is protected against physical damage as specified in 250.10.

Author's Comments:
a See 250.52(A)(5) and 250.53(A) for additional details.
a When the grounding electrode attachment fitting is located underground, it must be listed for direct soil burial [250.68(A) Ex. 1, and 250.70].
(H) Ground Plate Electrode. A plate electrode with not less than 2 sq ft of surface exposed to exterior soils must be installed so that it's at least 30 in. below the surface of the earth [250.52(A)(6)].

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