Per 250.190(B), when grounding a 5kV rated service disconnect operating at 4.16kV, what is the minimum size grounding electrode conductor for this service to connect the non-current metal parts of the metal-clad enclosure to ground? Assume the largest service-entrance phase conductor is 350kcmil and the equipment involved is fixed equipment.

  1. 350kcmil aluminum
  2. 3/0 AWG copper
  3. 1/0 AWG copper
  4. 2 AWG copper

Answer: D

Per this new section of the Code, the minimum size of the grounding electrode conductor is based on the size of the largest ungrounded phase conductor. A quick check of Table 250.66 reveals that a 350kcmil copper phase conductor requires a minimum size 2 AWG copper grounding electrode conductor.

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