This particular example falls into an interesting corner case.
You have a conductor rated at 230A, with a load (presumably) of less than 225A, protected at the supply end by a 250A breaker and at the load end by a 225A breaker. This would be a tap except for the round up rule that permits a 4/0 to be considered fully protected by a 250A breaker as long as the load is less than 230A.
If the over-all load on the 500kcmil conductors is less than 380A, then the entire thing could be protected by a 400A breaker, and then the same mix of conductors (500kcmil and 4/0AWG) _would_ have to follow tap rules, and the >25 foot length would be a violation.
-Jon
