This is a 3-pole unit with fixed thermal and fixed magnetic settings, UL/CSA listed — meaning it meets North American panelboard and switchboard standards for branch circuit protection.
What the description tells a panel builder
The description decodes as: XT4L series, 250 A frame, TMF trip block adjustable from 30 A to 400 A, 3-pole, fixed thermal and fixed magnetic settings, UL/CSA certified. The TMF trip provides thermal-magnetic overload and short-circuit protection with a fixed magnetic pickup — no field-adjustable instantaneous setting. This is a panel-mount device, sized for standard MCC or distribution panel cutouts; verify mounting pattern against the existing bus or lug kit.
What the trip rating means for the circuit
The TMF 30-400 A thermal-magnetic trip allows the continuous current rating to be set anywhere between 30 A and 400 A via the thermal adjustment dial, while the magnetic (short-circuit) pickup is fixed relative to the selected thermal setting. This gives the specifying engineer flexibility to match the breaker to a specific load without changing the trip unit — useful when the same frame size is used across multiple motor or feeder circuits in a panel.