The Schneider Electric C12N3TM125B is a ComPacT NSXm moulded-case circuit breaker (MCCB) in the 160 N frame, 3-pole, rated 125 A at 40 °C with a thermal-magnetic TM-D trip unit. Built to EN/IEC 60947-2, it is suitable for isolation per that standard. The IP40 front face and IK07 impact resistance suit it for enclosed panel mounting where occasional tool contact or minor mechanical shock is expected — typical for industrial switchboards and commercial distribution boards.
Above that, the thermal element in the TM-D trip unit follows an inverse-time curve — the hotter the ambient, the sooner it trips. For panels running above 40 °C, derate per the manufacturer's curve; this is not a breaker you push to 125 A in a 50 °C enclosure without checking. For service continuity after a fault, the 50 kA is the number that governs coordination with downstream devices. Category A utilisation means it is not intended for frequent switching of motor starts; it is a distribution breaker, not a motor-circuit protector. Power dissipation is 9.3 W per pole, so 27.9 W total at rated load.
Mounting and connections
The 9-module pitch (81 mm wide, 137 mm high, 80 mm deep) fits standard DIN-rail enclosures with a backplate adapter. Connections are front-facing on both line and load sides, accepting compression lugs or busbars. Connection pitch is 35 mm with spreaders, 27 mm without — check your lug centre spacing before terminating.