What it is and what it does
The Schneider Electric C12F6TM125B is a ComPacT NSXm moulded-case circuit breaker (MCCB) with a 125 A rated current at 40 °C, 4 poles, and a 36 kA breaking capacity at 415 V AC (performance level F). It uses a thermal-magnetic TM-D trip unit — the thermal element handles overloads, the magnetic element handles short-circuits — making it a straightforward choice for distribution panels where adjustable electronic trips aren't needed.
What the ratings mean for fit
The 125 A rating at 40 °C is the continuous current the breaker carries without tripping in a 40 °C ambient. If your panel runs hotter, you'll need to derate — the IEC 60947-2 standard this breaker is certified to (EN/IEC 60947-2) provides the derating curves. The 36 kA at 415 V AC is the maximum fault current it can safely interrupt; that's an F-class performance level, which covers most commercial and light industrial distribution boards. The 4-pole configuration (4P) switches all three phases plus neutral, with the neutral on the left. The breaker is also certified for isolation — so it can serve as a visible-break disconnect point, saving a separate isolator.
Where it fits in the panel
Mounts on a backplate — not DIN rail — so plan for a drilled panel or a mounting plate. It's 108 mm wide, 137 mm high, 80 mm deep, and takes 12 module pitches of 9 mm. Connection is front-to-front with compression lugs or busbars. The IP40 front face keeps tools and fingers out but isn't sealed against water — keep it in a dry enclosure. Pollution degree 3 means it's rated for conductive dust and occasional condensation, typical of a control cabinet in a factory environment.