For a 200-A service with a transformer feeding a single set of 3/0 AWG feeders, the largest copper GEC size to the water line is ___ AWG.

For a 200-A service with a transformer feeding a single set of 3/0 AWG feeders, the largest copper GEC size to the water line is ___ AWG.

• A. 2
• B. 4
• C. 3
• D. 1/0

Answer: (A)

Grounding electrode conductor size to a water pipe is set by NEC 250.66 and is based on the rating of the service equipment (or the overcurrent device protecting it). For a 200-A service, the minimum copper GEC size to the water line is two AWG. The presence of a transformer feeding a single set of 3/0 feeders does not change this requirement—the electrode conductor sizing is tied to the service rating, not the feeder size. Smaller than the minimum would not satisfy the code; larger sizes are permissible but typically the minimum that meets the requirement is the standard answer.

Grounding electrode conductor size to a water pipe is set by NEC 250.66 and is based on the rating of the service equipment (or the overcurrent device protecting it). For a 200-A service, the minimum copper GEC size to the water line is two AWG. The presence of a transformer feeding a single set of 3/0 feeders does not change this requirement—the electrode conductor sizing is tied to the service rating, not the feeder size. Smaller than the minimum would not satisfy the code; larger sizes are permissible but typically the minimum that meets the requirement is the standard answer.