What the 225 A rating means on this frame
The ABB XT3NU3150AFF000XXX is a Tmax XT3N frame breaker rated 225 A continuous, 3-pole, with a fixed thermal-magnetic trip unit adjustable from 150 A to 1500 A. That 225 A is the frame's maximum continuous current — the trip unit itself can be set lower via the thermal dial, but the frame and terminals are sized for the full 225 A. In a panel, that means the bus bars, lugs, and enclosure cutout must match a 225 A frame, even if you dial the trip down for a smaller load.
Mounting and terminal detail
Frame-mounted with front flat terminals — no DIN rail on this one. The flat terminals accept standard bus bar or cable lug connections on the line and load side. For a panel builder, that means planning the gland plate and bus bar drill pattern around a fixed-footprint breaker, not a snap-on unit. The XT3N frame is common across the Tmax line, so the cutout and mounting hole pattern carry over if you later swap to a different XT3N rating.