The Siemens 5SM3342-6BA is a SENTRON residual current circuit breaker (RCCB) — 4-pole, Type A, rated 25 A at 400 V AC, with a 30 mA trip threshold. It's an instantaneous device (no short-time delay), so it clears ground faults the moment leakage exceeds 30 mA. Type A means it catches both sinusoidal AC fault currents and pulsating DC fault currents from rectified loads like switching power supplies or variable-speed drives. Mounts on DIN rail (REG profile), occupies 4 width units, and accepts conductors from 1.5 mm² up to 25 mm². IP20 rating is standard for enclosed distribution boards. Overvoltage category III applies.
The 30 mA trip is the critical number for personnel protection. If your circuit has leakage from filters or VFDs that exceeds 30 mA under normal operation, this RCCB will nuisance-trip — you'd need a higher threshold or a Type B device. The 25 A current rating matches a 4-pole circuit feeding a 25 A load; the 400 V AC rating covers 3-phase systems up to that line voltage. Surge current resistance of 1 kA means it withstands lightning-induced or switching surges without welding the contacts. Mechanical life is 10 000 switching cycles typical — that's fine for a protection device that operates rarely; not a switching contactor that cycles every minute.
DIN-rail snap-on, any mounting position. Supply from top or bottom. Installation depth is 70 mm. Silicon-free construction.