I believe you are refering to Exception # 3 of the Art 230.90 (A)…however it is common practice to envoke 310.15(B)(6) which allows for 4/0 AL to a 200A panel…the ability to tap the service entrance meter cab into two individual protected panels of combined 400A via this method using (2) individual 4/0 AL cables.
Panels for general residential wiring come in normal 100,125,150 and 200 Amp rated formats…However meter cabs usualy are in a broader range of usage.
It is totally acceptacle for the Electrician to provide the service in this method.
230.71 Maximum Number of Disconnects.
(A) General. The service disconnecting means for each service permitted by 230.2, or for each set of service-entrance conductors permitted by 230.40, Exception Nos. 1, 3, 4, or 5, shall consist of not more than six switches or sets of circuit breakers, or a combination of not more than six switches and sets of circuit breakers, mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be no more than six sets of disconnects per service grouped in any one location. For the purpose of this section, disconnecting means used solely for power monitoring equipment, or the control circuit of the ground-fault protection system or power-operable service disconnecting means, installed as part of the listed equipment, shall not be considered a service disconnecting means.
The key is 230.2 supports this…
BUT with that said…maybe I am getting too technical here versus the question…because I seem to have forgotten the question…thehehehe
I think in the end all you can do as the HI is look at the sizes of the conductors, look at the service size at the loop and also look for signs of overheating and so on.
As for calculations…we have just developed the concept of CALC on services under 3,500 sq ft and when they are over 3,500 sq ft…400A automatically unless the house is excessive…BUT it is very rare to need more than 400A in service…to an electrician if more is needed even before calculations take place…it will be obvious to the trained eye…or should I say…BATTLE TESTED eye…lol
No problem mate ( I got the mate part from GERRY…thehehe ) just figured they would like to know how electricians think when sizing and so on.