The Siemens 5SM3642-4KK14 is a 4-pole residual current circuit breaker (RCCB) from the SENTRON 5SM3 series, designed for 400 V AC systems at 50/60 Hz. Rated at 25 A continuous with a 10 kA short-circuit current rating (SCCR), it's sized for sub-distribution boards feeding mixed loads. The short-time delayed design (S-type) provides selectivity with downstream RCCBs, so a fault on a branch trips the branch device rather than this main unit — keeps the rest of the board live.
The 25 A rating holds at 40 °C and 45 °C; derate to 24 A at 50 °C, 23 A at 55 °C, and 22 A at 60 °C, down to 20 A at 70 °C. If your enclosure runs warm, use the 50 °C column for sizing — a 25 A circuit on a hot panel floor may need the next frame up. That's standard for most commercial sub-distribution; verify against your transformer size and cable length if the available fault current exceeds 10 kA. Type B+ detection covers AC, pulsating DC, and smooth DC fault currents up to the rated residual current. The surge current resistance of 3 kA (8/20 µs waveform) means it won't nuisance-trip on lightning-induced surges common in industrial mains. The I²t rating of 70,000 A²s gives coordination data for upstream MCBs or fuses — useful when building a selective distribution board per IEC 60947-2.
Occupies 4 width units (72 mm wide, 90 mm tall, 77 mm deep with 70 mm installation depth). Mounting position is unrestricted — horizontal, vertical, or flat — which helps in tight enclosures.