What it is and what it does
The Siemens SENTRON 5SM3648-0 is a 4-pole residual current operated circuit breaker (RCCB), type AC, rated 100 A at 400 V AC with a 300 mA trip threshold. It's an instantaneous-trip device — no intentional delay, so it clears a ground fault as fast as the waveform lets it. The 10 kA short-circuit current rating (SCCR) per EN 60898 and IEC 61008-1 means it can safely interrupt a bolted fault up to that level without welding contacts or cascading upstream. That's the number that governs selectivity coordination in a distribution board.
Mounting and panel fit
Snaps onto DIN rail (REG profile), 4 modular width units wide, 70 mm installation depth. Mount in any position — no derating for orientation. Supply can land top or bottom; the device is polarity-insensitive for the residual current sense. IP20 with the distribution board installed and conductors connected — treat it as a panel-internal device, not for wet locations.
Thermal limits and power loss
Rated operating ambient -5 °C to 45 °C. Storage range is wider: -40 °C to 75 °C — that's the handling limit, not the running limit. Each pole dissipates 8.9 W at rated current in hot operating state, so a 4-pole block pushes about 35.6 W into the enclosure. That matters for fill factor and derating if the panel is tightly packed.