The ABB XT1NU4040AAA000XXX is a molded case circuit breaker from the XT1N series, built around a 125 A frame and fitted with a TMF 40-500 thermal-magnetic fixed trip unit. The 4-pole configuration with line/load side lug terminations suits it for three-phase plus neutral applications in panelboards and distribution boards. The UL/CSA listing on the nameplate confirms acceptance for North American installations per UL 489 and CSA C22.2 No. 5.
What the description tells you
The description string 'XT1N 125 TMF 40-500 4P FF UL/CSA' decodes to a 125 A frame size with a TMF trip unit adjustable from 40 A to 500 A. The 'FF' indicates fixed thermal and fixed magnetic settings — no field-adjustable dials. The 4-pole version with front-face (FF) terminals is the standard panelboard configuration. The UL/CSA suffix means the breaker carries both UL and CSA certifications, so it meets code requirements in the US and Canada without additional agency marks.