The smallest size grounding electrode conductor connected to a ground ring from a 225-A, main breaker service panelboard is ___ AWG. The service panelboard is fed with four 4/0 AWG conductors and the ground ring is a 2 AWG copper conductor.

The smallest size grounding electrode conductor connected to a ground ring from a 225-A, main breaker service panelboard is ___ AWG. The service panelboard is fed with four 4/0 AWG conductors and the ground ring is a 2 AWG copper conductor.

• A. 1/0
• B. 3/0
• C. 2
• D. 1

Answer: (C)

Grounding electrode conductor sizing is determined by NEC 250.66, which bases the minimum size on the largest service-entrance conductor feeding the panel. In this case, the service is fed with four conductors of 4/0 AWG copper, so the largest service-entrance conductor is 4/0 copper. The table for copper conductors shows that for 4/0 or larger service conductors, the minimum grounding electrode conductor size is 2 AWG copper. Since the ground ring is already 2 AWG copper, it meets the minimum requirement, making 2 AWG the smallest permissible size. Any smaller size would not meet the code, while larger sizes would also be acceptable but not required here.

Grounding electrode conductor sizing is determined by NEC 250.66, which bases the minimum size on the largest service-entrance conductor feeding the panel. In this case, the service is fed with four conductors of 4/0 AWG copper, so the largest service-entrance conductor is 4/0 copper. The table for copper conductors shows that for 4/0 or larger service conductors, the minimum grounding electrode conductor size is 2 AWG copper. Since the ground ring is already 2 AWG copper, it meets the minimum requirement, making 2 AWG the smallest permissible size. Any smaller size would not meet the code, while larger sizes would also be acceptable but not required here.