The ABB XT1SU3045AFF000XXX is a molded case circuit breaker (MCCB) from the XT1S series, sized for a 125 A frame with a TMF 45-500 thermal-magnetic fixed trip unit. The three-pole design with front terminals suits it for panelboard or distribution-board mounting where you need overcurrent protection on a 400 VAC or 480 VAC feeder.
The 125 A frame and TMF 45-500 trip unit mean the breaker is sized for a circuit where the continuous load is up to 125 A, and the thermal-magnetic trip provides both overload (thermal) and short-circuit (magnetic) protection. The "45-500" indicates the magnetic pickup range — typically 5x to 10x the rated current, so it clears faults fast without nuisance tripping on motor inrush. UL/CSA listing certifies it for North American panel installations per UL 489 and CSA C22.2 No. 5.