Services are popularily sized per the combined ratings of the service disconnects, despite 250.66 requiring the GEC based on the size of the SEC.
230.23(A) sizes the SDL, 230.42(A) sizes the service entrance conductors, 230.71(A) allows up to six service disconnects, and 230.90(A) requires the OC device to be rated no greater than the ampacity of the service entrance conductors.
Schockme, I wouldn't call your service 300 amps, unless you installed two 150 amp mains.
2/0 copper is good for 200 amps per 310.15(B)(6) for residential services, you have two 200 amp mains and panels, for a combined 400 amps of capacity. I'd call that a 400 amp service.
230.90(A) exception #3 allows the sum of the ratings of the 2-6 circuit breakers to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.
