I have a 400a Homeline main panel that has two 200a breakers in it, they are fed from factory installed paralleled 3/0. I ran a #2 to the water main, and the inspector wants a larger conductor. My argument is for the paralleled 3/0 a #2 is what code calls for. His argument is that it is 400a panel and the ground needs to be based on 400a. I should add this is an underground fed panel, and the utility conductors are 350 AL. Any comments would be appreciated.