I just want to interject. I've been reading through some of these, and just want to make clear that some of this is incorrect. Someone mentioned that if it's not CT'd that it has to be a 320 amp service. That's not the case at all. Many companies allow the use of 400 amp self contained metering. His metering has 400 amps of breaker behind the metering. If this were only a 320 amp meter set - if he follows NEC - the main would have 300 amps behind the meter (two 150 amp breakers - or any other configuration that wasn't above 300 amps). This is very likely a 400 amp meter loop.
As far as the utility company only using 350 MCM. You must understand that a home owner / electrician needs to follow NEC rules and regulations. Utility companies are required to use NESC rules and regulations. There is a 40% conductor rating difference between the two standards. A utility company also is only required to size their service to actual load - including diversity. NEC sizing pushes an electrician to size the entrance cable to panel size.
I am an engineer for a large utility company in the midwest. There have been more than one time I've installed very small conductor to a customer that had a very large service. Usually this ends up in the electrician/homeowner freaking out. I explain things to them - tell them if they have voltage flicker (due to our conductor being sized too small) that I will come right back and change it out. I have never, not once, been called back.
In other words - I would not worry for a minute that all they installed was 350 MCM. According to NESC specs - 1 run of 350 MCM w/ a 4/0 neutral - direct buried is capable of 508 amps and installed in duct is 397 amps. You're more than covered. If I was the engineer - depending on the length - you may have gotten smaller conductor installed.
