The Siemens 5SV3742-4 is a SENTRON residual-current circuit breaker (RCCB) rated at 25 A with a 500 mA tripping fault current, 4-pole, Type B, short-time delayed. It's built for DIN-rail mounting in distribution boards — 4 modular width units (72 mm wide) and 70 mm deep, so it wires up clean in a standard enclosure. The Type B detection handles smooth DC, pulsed DC, and AC residual currents, which matters when you've got VFDs, UPS systems, or EV chargers on the circuit — those loads can throw DC fault currents a standard AC/Type A RCCB won't see.
Mounts on DIN rail (REG) in any position — no derating for orientation. IP20 with connected conductors and installed distribution board, so it's for indoor panel use only, not washdown. The short-time delayed design (Type S equivalent) means it coordinates with downstream RCCBs to avoid nuisance tripping on transient leakage. Rated short-circuit current 10 kA per IEC 61008-1 and EN 60898 (0.8 kA). Overvoltage category III. Silicon-free construction.