I'm installing some new drives, and am using an old existing cabinet that's already wired with 480VAC. The cabinet has a 250A breaker in it, fed by three 3/0 copper (90c) cables... which are fed from a 250A breaker in an MDP. The cabinet used to house a motor starter. The NEC says that 3/0 copper (90c) cables in conduit/raceway have an ampacity of 225A. Was the cable undersized from the beginning? Or was there some exception where this was allowed? The cabinet was probably installed around 1997.