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.

Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at necexpert@aol.com.