What the TMF 150-1500 trip means for your panel
The XT4LU3150AFF00NXXX: The TMF 150-1500 designation tells you the trip unit is a thermal-magnetic fixed type, adjustable across a 150 A to 1500 A range. That's a wide band — you dial it in for the actual load, not the breaker's ultimate interrupt capacity. The thermal element handles overloads (slow, heat-based), and the magnetic element catches short-circuit faults (instantaneous). For a 3-pole unit on a 480 V motor circuit, you'd typically set it around 125% of the full-load amps per NEC. The UL/CSA listing means it's accepted in North American panels without extra paperwork.