The ABB XT2LU3040AFF00NXXX is a molded case circuit breaker from the XT2L series, rated 125 A frame with a TMF 40-400 A thermal-magnetic trip unit, 3-pole, with front terminals and UL/CSA certification.
The TMF 40-400 A trip unit gives you a thermal-magnetic curve adjustable across that range, so you can set the overload and short-circuit protection to match the downstream load — motor, feeder, or distribution. The 125 A frame means the breaker itself is sized for continuous current up to 125 A, but the trip unit can be set lower (down to 40 A) to protect a smaller conductor or device. The 3-pole configuration handles three-phase circuits, and the front terminals simplify panel wiring and busbar connections.
It is used for branch-circuit protection in industrial control panels, motor control centers, and distribution boards — the UL/CSA listing means it is accepted in North American installations as well as IEC markets.