You are installing a GEC to the main water line from a 200-A, main breaker Panel LC. ___ AWG is the largest size copper wire required. As shown in the data, the panel is fed from a transformer with one set of 3/0 AWG wire.

You are installing a GEC to the main water line from a 200-A, main breaker Panel LC. ___ AWG is the largest size copper wire required. As shown in the data, the panel is fed from a transformer with one set of 3/0 AWG wire.

• A. 2
• B. 4
• C. 3
• D. 1/0

Answer: (D)

The sizing of a grounding electrode conductor (GEC) is driven by the size of the service or feeder that is connected to the structure. In other words, the larger the feeder or service rating, the larger the GEC that is required to provide a low-impedance path for fault currents back to the source so that overcurrent protective devices can trip properly. Here, the panel is fed from a transformer with a very large feeder conductor (3/0 AWG copper). When the NEC sizing rules are applied to a feeder of this size, the minimum copper GEC size to connect to the water service (the grounding electrode) comes out to 1/0 AWG. That means you must have at least 1/0 AWG copper for the GEC to the water line; any smaller conductor would not meet the required minimum for this configuration. The other smaller options would not satisfy the required minimum, so they aren’t acceptable in this setup. The key takeaway is that the GEC must be sized up to match the capacity of the service/feeder feeding the panel.

The sizing of a grounding electrode conductor (GEC) is driven by the size of the service or feeder that is connected to the structure. In other words, the larger the feeder or service rating, the larger the GEC that is required to provide a low-impedance path for fault currents back to the source so that overcurrent protective devices can trip properly.

Here, the panel is fed from a transformer with a very large feeder conductor (3/0 AWG copper). When the NEC sizing rules are applied to a feeder of this size, the minimum copper GEC size to connect to the water service (the grounding electrode) comes out to 1/0 AWG. That means you must have at least 1/0 AWG copper for the GEC to the water line; any smaller conductor would not meet the required minimum for this configuration.

The other smaller options would not satisfy the required minimum, so they aren’t acceptable in this setup. The key takeaway is that the GEC must be sized up to match the capacity of the service/feeder feeding the panel.