This is the core overcurrent protection device for a distribution panel or motor control center branch — the 3-pole configuration handles three-phase loads, and the TMA trip gives you adjustable thermal (overload) and fixed magnetic (short-circuit) protection curves. The lifecycle stage is current, meaning it remains in ABB's active catalog and is not subject to a last-time-buy window.
The 3-pole design means it occupies three module widths — factor that into your panel fill calculation alongside the upstream feeder breaker and downstream load terminals. The TMA trip unit's thermal adjustment range lets you fine-tune the overload pickup to match motor or transformer inrush without nuisance tripping, while the fixed magnetic setting clears hard faults fast enough to maintain selectivity with downstream branch breakers.
Comparison with XT5NU340ABNF000XXX
The XT5NU340ABNF000XXX is a physically larger XT5 frame breaker rated 400 A at 690 V AC, also 3-pole. It will not drop into a panel cutout or DIN-rail footprint designed for the XT2L frame — the XT5 requires wider spacing and higher bus-bar ampacity. If your BOM originally specified the XT5NU340ABNF000XXX, the XT2LU3125BBB000XXX is not a form-fit replacement; the two serve different current tiers (125 A vs 400 A) and different frame sizes. The XT2LU3125BBB000XXX is the correct choice for a 125 A branch; the XT5NU340ABNF000XXX belongs at the feeder or main level.