The TMF designation means the thermal and magnetic settings are factory-fixed — no field-adjustable dials for long-time or short-time pickup. That locks the protection curve to a single characteristic, which simplifies coordination studies but removes the flexibility to retune for a different load later. For a panel builder, this is a straight drop-in for a fixed-load feeder or a motor branch circuit where the full-load amps are known at design time.
The XT3S platform is ABB's compact MCCB family, sized for panelboard and distribution board integration where space is tight. The 225 A frame covers feeder circuits from moderate motor loads up to lighting and resistive heating banks. The TMF trip unit provides thermal protection against sustained overloads and magnetic protection against short-circuits, with no electronic trip module to power or program.