I'm used to seeing either Iu or In, or the two identical, but I recently came across a molded case breaker (GE D125) that had an Iu=125A and In=100A, (adjustible from 75-100A). It's not a plug, it's built into the breaker and can't be changed beyond the pot. What, exactly, does this mean? As I understand it, Iu=125A means the contacts are rated for 125A... but with a 100A trip setting, why does that matter in the least? Why would they even bother labeling it? Am I missing something here?

Could this be a 125 Amp frame, with a 100 Amp trip?

Kind of looks that way from the Spec # (GE D 125), but who knows.

Let me check the GE catalog, then reply later.

Scott

That's my working assumption, too, Scott. I hate guessing about things like this, though.