The Schneider Electric C12B6TM125B is a ComPacT NSXm 4-pole moulded-case circuit breaker with a TM-D thermal-magnetic trip unit rated 125 A at 40 °C.
The 125 A rating at 40 °C is the continuous current the breaker can carry in a 40 °C ambient — push the ambient higher and you need to derate. The TM-D trip unit is thermal-magnetic: the thermal bimetal handles overloads (slow, inverse-time), the magnetic coil handles short-circuits (instantaneous). 25 kA at 415 V AC is the SCCR; if the available fault current at the panel is higher, this breaker isn't the right call — you'd need the 36 kA or 50 kA variant in the same frame. The 4-pole configuration means it switches all three phases plus the neutral, with the neutral on the left. Isolation suitability per IEC 60947-2 means you can use it as a disconnecting means — no separate isolator needed upstream.
Panel integration
Mounts on a backplate in either horizontal or vertical orientation, flat on the back. The 108 mm width spans 12 module pitches at 9 mm — that's the DIN-rail footprint it occupies. Connection terminals accept compression lugs or busbars, both top and bottom front-connected. Connection pitch is 35 mm with spreaders, 27 mm without. IK07 impact rating handles light mechanical shock during panel assembly.