Re: AF and AT breaker notation
I trust that this will explain frame sizes. It is ment to be a general overview only.
With regard to industrial breakers frame sizes generally run 100(F), 150(F)to 225a, 250(J), 400(K), 600(L), 800(M), 1200(N), 2000(P),and 2500(P).
The there are non-interchangable and interchangable trips, NIT and IT.
U[ to 150a there are no choices, they are NIT. There are some that are available up to 225a in the 150a frame size.
Frames 250a and larger are available in either NIT and IT. Also, 440a and 600a frames are often times the same size. The 800 and 1200a are also the same size with the 1200a being a greater depth.
There are numerous varieties of the larger 2000a and 2500a breakers.
Breakers sizes 400a and above have electronic trips available with include long and short time delay, adjustable instantaneous, ground fault pick-up and delay etc, with easily changable rating plugs it shange the trip rating withput complete disassembly of the breaker.