What it is and what it does
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.
What the ratings mean for fit
The 10 kA short-circuit current rating (SCCR) tells you this RCCB can safely interrupt a fault up to that level at 400 V — it won't weld its contacts or arc over catastrophically. The 300 mA trip threshold is typical for whole-panel or feeder protection, not individual socket circuits (those usually run 30 mA). The 4-pole, 4-module-width (72 mm) body clips onto standard DIN rail, and the mounting position is unrestricted — any orientation works in the enclosure.
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. If your panel runs hot — say a packed enclosure near a drive — factor that in. Storage range is wider: -40 °C to 75 °C, so it handles warehouse or truck-bed extremes before installation.
Panel integration notes
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. IP20 with conductors connected — standard for enclosed distribution boards, not for wet or dust-prone locations without a cover.