Given: A 120/208V, 3 phase service is fed with a single size 500KCMil, copper conductor for each phase. The main circuit breaker is rated at 300 amps. A copper grounding electrode conductor from the main service panel to the cold water pipeline must be at least size ____.

Given: A 120/208V, 3 phase service is fed with a single size 500KCMil, copper conductor for each phase. The main circuit breaker is rated at 300 amps. A copper grounding electrode conductor from the main service panel to the cold water pipeline must be at least size ____.