What the Ratings Mean for Fit
The XT1NU4020AAA000XXX: The 125 A frame and TMF 20-500 A trip unit mean this breaker accepts a continuous current rating set between 20 A and 500 A via the interchangeable trip block. The 4-pole configuration handles three-phase plus neutral switching, common in North American panelboards where a switched neutral is required. The UL/CSA listing certifies compliance with UL 489 and CSA C22.2 No. 5 — the standard for molded case circuit breakers in branch-circuit protection. The front terminals accept standard bus bar or cable connections; verify lug size against your wire range before panel assembly.