When installing a GEC to the main water line from a 200-A main breaker, what is the largest size copper wire required?

When connecting a ground electrode conductor (GEC) to the main water line, it's crucial to adhere to the National Electrical Code (NEC) requirements pertaining to wire sizes based on the service rating. For a service of 200 amperes, the NEC specifies that the minimum size of copper wire required for the GEC is a certain gauge.

According to NEC Table 250.66, when the grounding electrode is a metal water pipe, the size of the GEC must be based on the largest ungrounded service-entrance conductor. For a 200-A service, the minimum size copper wire permissible for grounding purposes is indeed 4 AWG. This ensures a safe and effective grounding system that can handle possible fault conditions, reducing the risk of equipment damage and maintaining safety for personnel.

Larger wires, such as 2 AWG or 1/0 AWG, would exceed the minimum requirement for this scenario, while a wire size of 3 AWG also does not meet the NEC criteria for a 200-A service. Therefore, 4 AWG copper wire is the correct size needed for the proper connection to the main water line as the GEC, ensuring compliance with safety standards.