200A service with 4/0 alum. cond. what size GEC is okay? i know that table 250.66 says #4 but im in an arguement with someone who says it's not required to be any larger than #6. also, there is no rebar ground and plastic water service. what do you say?

250.66(A) says #6.

A driven ground never needs more than #6 cu. Any other electrode, #4 cu.