I am uncertain as to when this section can be sited as a reason for utilizing a breaker with a rating above the ampacity of the conductors being protected. Say, for instance, the ampacity (after all derating) of a set of service conductors is 380A. Since, according to 240.6(A), standard breaker size jumps from 350 to 400A, can the conductors with an ampacity of 380A feed a 400A service?