The Siemens 5SM3648-8 is a SENTRON selective residual current circuit breaker (RCCB), 4-pole, type A, rated 100 A with a 300 mA residual operating current and 400 V AC at 50 Hz. The selective design (short-time delayed) means it coordinates with downstream RCCBs — in a fault, the downstream device trips first, keeping supply to the rest of the distribution board. That 300 mA threshold is sized for whole-circuit protection rather than individual equipment, so it suits sub-distribution boards feeding multiple final circuits.
The 1 kA rating per EN 60898 is a separate standard for domestic-type breakers; the 10 kA figure governs industrial installation. Type A detection covers AC residual currents and pulsating DC — the common waveform from single-phase rectifiers in electronics, drives, and LED lighting. The 300 mA sensitivity is deliberately less sensitive than a 30 mA unit, so it won't nuisance-trip on normal leakage from long cable runs or multiple loads.
Depth is 77 mm, installation depth 70 mm — verify enclosure depth if the panel has a shallow backplate or door-mounted devices. IP20 with conductors connected and distribution board installed — not rated for wet or dusty environments. Silicon-free construction, which matters for potting or conformal-coating compatibility in sensitive electronics enclosures.