The C12H3TM125B is a Schneider Electric ComPacT NSXm 160H frame moulded-case circuit breaker, 3-pole, rated 125 A at 40 °C with a thermal-magnetic TM-D trip unit. The 125 A rating matches motor feeder or main distribution loads; the thermal-magnetic trip gives instantaneous short-circuit and inverse-time overload protection in one package. Mounts on a backplate, front-connected top and bottom via compression lugs or busbars, and fits a 9-module pitch at 81 mm wide — standard DIN-rail panel layout. IP40 front face keeps dust out; IK07 impact rating handles tools dropped during service. The toggle handle gives positive visual indication, and the green flag signals auxiliary contact presence.
Most industrial 415 V distribution boards with a transformer under 1 MVA stay under 50 kA, so this H-rated unit gives headroom without over-spec'ing. The 125 A TM-D trip handles copper loads up to that continuous current; the thermal element tracks heating, the magnetic element clears bolted faults instantly. Operates at 50/60 Hz, 0–95% RH, up to 2000 m without derating (5000 m with derating). The 137 mm height and 80 mm depth leave room for wiring gutters in a standard 600 mm deep panel.