What is the maximum size of the Grounding Electrode Conductor (GEC) for an AC ungrounded system when it's the sole connection to a made electrode?

The maximum size of the Grounding Electrode Conductor (GEC) for an AC ungrounded system, when it serves as the sole connection to a made electrode, is determined by electrical codes and standards that ensure safety and proper functioning. In this case, No. 6 is the correct choice because it is commonly specified in the National Electrical Code (NEC) as the appropriate size for the GEC in such contexts.

Using a No. 6 conductor ensures that there is sufficient current-carrying capacity and mechanical strength to handle potential fault currents that may occur even in ungrounded systems. It also helps maintain system safety by providing an adequate grounding path should a fault condition arise, reducing the risk of electric shock or fire.

In contrast, larger sizes like No. 4 may be excessive and could lead to unnecessary complexity or cost without a corresponding benefit in performance. Smaller sizes such as No. 8 or No. 10 do not provide sufficient capacity to safely handle fault conditions, creating potential safety hazards. Hence, No. 6 is the right choice as it balances safety, compliance, and practicality for ungrounded systems with a single made electrode connection.