The ABB XT1SU3045AYD000XXX is a 3-pole molded case circuit breaker on the NEXT1S 125 frame, fitted with a TMF (thermal-magnetic fixed) trip unit rated 45-500 A. It's built for UL/CSA-marked distribution panels, motor branch circuits, and feeder protection in industrial and commercial installations where the 125 A frame gives headroom for the 45-500 A trip range. The TMF trip delivers a fixed thermal curve for overloads and a magnetic pickup for short-circuits — no field-adjustable dials, which means the trip setting is locked at the factory and stays consistent across the installed base.
The 125 A frame size tells you the breaker's mechanical and thermal capacity, not the trip setting — the TMF trip unit is set at 45-500 A, so you order the exact continuous-current rating that matches your load. That 3-pole configuration covers three-phase circuits; the 'F F' designation indicates fixed front terminals (line and load), which simplifies bus-bar layout and reduces wiring errors compared to plug-in or rear-connection variants. UL/CSA listing means the breaker is accepted for North American panel builds without additional agency review — a time-saver for panel OEMs shipping to US or Canadian sites.