What is the MINIMUM size copper conductor that is permitted to be used as a grounding electrode conductor for a service using 3/0 copper conductors?

The minimum size copper conductor permitted to be used as a grounding electrode conductor is determined by the size of the service conductors. In this scenario, since the service is using 3/0 copper conductors, the grounding electrode conductor must be sized accordingly to ensure adequate grounding and bonding.

According to the National Electrical Code (NEC), for copper conductors when the largest ungrounded service conductor is 3/0 AWG, the minimum size for the grounding electrode conductor is #4 AWG copper. This sizing is essential for ensuring that the grounding system can safely conduct any fault currents back to the ground, thus providing a safe path to dissipate electricity and protect both equipment and personnel from electrical hazards.

Using a grounding electrode conductor smaller than #4 AWG in this case would not meet the NEC requirements, potentially compromising the safety of the electrical installation. Therefore, #4 AWG copper is the appropriate choice for this application, as it satisfies the code requirements while also maintaining effective grounding practices.