The state I used to work it, it was common pratice for a 400amp residential service to really be a 320amp. The meter was a 320amp rated meter socket that feed 2 200amp (main breaker) panels with 2" pipes and 3/0's to each panel. I have changed to a different region, and am wondering if this is standared everywhere or if this is not the right way to do this.
Common practice in Mass. 320 amp continuous for a 400 amp service. 80%. I believe you have to be the full 400 amp on commercial services. Most of the electricians around here install it exactly how you explained except they use 4/0-3 SEU/AL. No pipe. Your way is much better, I guess around where I am they go the bare minimum requirements.
Thats how the 400 amp resedential are set up around here in IL. We don't call it a (2) 200 or 320 amp. Maybe more of a sales thing. Don't want to be pricing out a 320 amp when the other EC has the same set up calls it a 400 amp.
At the supply we just ask for a 400 amp pedistal but they know we mean 320 amp. Milbanks catolog for Com Ed only shows single phase 320 not 400 amp meter housings. Com Ed resi feeds underground are normaly 200 and 320 a. Overhead 100, 200, and 320 a.
We would only bond one panel and would run a larger water pipe ground than a single 200 a service, I think 1ott. You could do it other ways.