A. Branch-circuit conductors must have an ampacity of not less than the maximum load to be served. Conductors must be the larger of 210.19(A)(1)(a) or (b): (a) Conductors must be sized no less than ...

Feeder and service load calculation requirements can be found in Part III of Art. 220 in the 2014 NEC. As noted in Sec. 220.52(B), "A load of not less than 1,500VA ...