The Siemens 5SM3642-4 is a 4-pole SENTRON residual current circuit breaker (RCCB) rated 25 A at 400 V AC, 50/60 Hz, with a 300 mA Type B residual-current trip. Type B means it catches smooth DC fault currents up to the rated value, not just AC or pulsed DC — the right pick for VFD, UPS, or PV circuits where pure DC leakage can blind a standard AC/Type A device. The short-time delayed (selective) design lets it ride through transient earth faults and coordinate with downstream RCCBs, so only the faulted branch trips.
The 300 mA trip threshold is typical for whole-panel or feeder protection, not individual socket circuits (those usually run 30 mA).
Derating and ambient limits
At 45 °C ambient it still carries the full 25 A. Above that, derate: 24 A at 50 °C, 23 A at 55 °C, 22 A at 60 °C, 21 A at 65 °C, 20 A at 70 °C.
Snaps onto DIN rail (REG profile). Depth is 77 mm, installation depth 70 mm — check your enclosure depth before wiring. Supply can land top or bottom; the SIGRES function (if used) needs bottom feed to stay live in the off state.