MCCB for panel build
The ABB XT3NU3125AAA000XXX is a 3-pole molded case circuit breaker from the XT3N 225 frame, fitted with a TMF 125-1250 thermal-magnetic fixed trip unit and UL/CSA certification. This is the standard MCCB for a 225 A frame panelboard — sized for feeder or large motor branch circuits where the 125-1250 A trip range covers the load.
What the rating means
The TMF 125-1250 designation means the thermal-magnetic trip unit is adjustable between 125 A and 1250 A — that is the continuous current rating range, not a fixed value. The 225 A frame (XT3N 225) limits the maximum withstand to 225 A in the standard configuration, so the trip setting must be coordinated with the frame. Three poles cover three-phase circuits up to 480/600 VAC typical for UL 489 applications. UL/CSA listing means it passes the full UL 489 interrupting and endurance tests — required for service-entrance or feeder duty in North American code jurisdictions.