The Siemens SENTRON 5SM3445-0 is a 4-pole residual current operated circuit breaker (RCCB), type AC, rated 125 A with a 100 mA trip threshold. It operates on a 400 V AC, 50 Hz supply and carries a 10 kA short-circuit current rating (SCCR) per IEC 61008-1 and EN 60898. This is an instantaneous-trip device — no intentional short-time delay on the residual current path — so it clears fast on a ground fault. The type AC designation means it detects sinusoidal AC residual currents only; it is not rated for pulsating DC or smooth DC faults, which matters if the downstream load includes rectifiers, VFDs, or switching power supplies.
Panel fit and mounting
Snaps onto DIN rail (REG profile) and occupies 4 modular width units (72 mm wide). Installation depth is 70 mm; the overall depth including the front face is 77 mm. Mounting position is unrestricted — vertical, horizontal, or inverted — which simplifies panel layout when the busbar run forces an orientation. Supply can enter from top or bottom; the test circuit requires a minimum of 195 V to operate. The enclosure is IP20 with connected conductors — fine for a closed distribution board, not for a washdown environment.
Environmental and mechanical limits
Operating ambient range is -5 °C to 45 °C; storage range extends from -40 °C to 75 °C. Rated for overvoltage category III and surge current resistance of 1 kA. Mechanical service life is 10 000 switching cycles typical. The device is silicon-free, which avoids outgassing issues in sealed or sensitive electronic compartments.