Hey, anyone want to tell me the de-rating?

The engineer has decided for reasons that I am not privy to, to spec a 125a 3pole on the switch gear to feed the sub panel I hope to be installing next week.

He had originally drawn it with a 100a 3pole, and spec'd #1 cable.

I'm going to need to pull 1/0, yes?

I don't work a lot of three phase. Happily the switch gear is less than a year old, and there is a blank open for the new breaker.

Not like some Frankenstein equipment in some damp basement.