The largest size grounding electrode conductor required is _____ copper.
a) 6 AWG
b) 1/0 AWG
c) 3/0 AWG
See answer and applicable Code reference
The correct answer is: c) 3/0 AWG
Article 250 covers general bonding and grounding requirements. As noted in Sec. 250.66, the size of the grounding electrode conductor at the service, at each building or structure where supplied by a feeder or branch circuit, or at a separately derived system of a grounded or ungrounded AC system shall not be less than given in Table 250.66, except as permitted in 250.66(A) through (C). Looking at Table 250.66, we see that the largest size copper grounding conductor is 3/0 AWG.