The C25B4TM125 is a Schneider Electric ComPacT NSX250B moulded-case circuit breaker, 4-pole, fitted with a TM-D thermal-magnetic trip unit rated 125 A at 40 °C. This is the go-to MCCB for distribution boards, switchboards, and motor control centres where you need overload (L) and short-circuit (I) protection in one compact package — no add-on electronics, no earth-leakage module on this variant. At 220/240 V the same breaker delivers 40 kA Icu, which covers most North American distribution voltages with headroom. The trip unit is thermal-magnetic, meaning the thermal element handles sustained overloads and the magnetic element clears fast on high faults — no auxiliary power needed, no microprocessors to fail. Mount it flat on a backplate in any orientation, with front connections top and bottom.
Integration and mounting — panel fit
The breaker measures 161 mm high by 140 mm wide by 86 mm deep — standard NSX250B footprint, so it retrofits into existing ComPacT switchboard cutouts and busbar risers without re-drilling. Connection pitch is 35 mm, matching the standard busbar tap spacing.
Durability and duty — what 20000 cycles means for a distribution breaker
Mechanical durability is 20000 cycles; electrical durability varies with load: 20000 cycles at 440 V at half rated current (In/2), 10000 cycles at full rated current (In), and 5000 cycles at 690 V at In/2. For a distribution MCCB that sees infrequent switching (maybe a few operations per month), this is effectively a lifetime rating — you will not wear it out in normal service. If this breaker is used as a manual disconnect under load multiple times per shift, the 10000-cycle figure at full current is the one to watch; that still represents years of daily operation.