Re: Service entrance conductor sizing
From the NFPA NEC Handbook, "If a single set of 3-wire, single-phase, service-entrance conductors in raceway or cable supplies a one-family, two-family, or multifamily dwelling, the reduced conductor size permitted by 310.15(B)(6) is applicable to the service-entrance conductors, service-lateral conductors, or any feeder conductors that supply the main power feeder to a dwelling unit.
This section permits the main feeder to a dwelling unit to be sized according to the conductor sizes in Table 310.15(B)(6) even if other loads, such as ac units and pool loads, are fed from the same service. The feeder conductors to a dwelling unit are not required to be larger than its service-entrance conductors."
Please keep in mind that the opinions in the handbook are just that, opinions of the authors. The only way to get the Code Making Panel's opinion is to get a formal interpretation. In this particular case, I agree with the authors.
BTW, what is wrong with a pair of 200 ampere panelboards instead of a single 400 ampere panelboard? Both are 400 ampere services.
