From the original post.

Quote
Each box will have 2 #4/0 + ground wire

If this is fed from a 15, 20 or 30 amp circuit the EGC will have to be a 4/0 also. [Linked Image]

The EGC for these size circuits is a 1 to 1 ratio and remains 1 to 1 no mater how big you make the ungrounded conductors. [Linked Image]

Bob

Bob Badger
Construction & Maintenance Electrician
Massachusetts