The Siemens SENTRON 5SM3618-0KK is a 2-pole residual current operated circuit breaker (RCCB) — a Type AC device rated for 100 A continuous load with a 300 mA trip threshold. It's an instantaneous design, meaning it clears a ground fault as soon as the residual current exceeds that 300 mA level, with no intentional delay. The 10 kA short-circuit current rating (SCCR) tells you it can safely interrupt a fault up to that level without welding its contacts or cascading damage upstream, which is the figure that matters for panel coordination studies.
Snaps onto standard DIN rail (REG profile) and occupies 2 modular width units — 36 mm of rail space. Installation depth is 70 mm, and it can be mounted in any orientation. Supply can enter from top or bottom, which simplifies busbar routing in a crowded distribution board. The IP20 rating applies once the board is installed with conductors connected; it's not a standalone outdoor device.
Ambient operating range is -5 °C to 45 °C, with storage extremes from -40 °C to 75 °C. The 45 °C ceiling is the limiting factor for panel placement — if the enclosure interior runs hotter than that, you need to derate or move the RCCB to a cooler zone. Mechanical service life is rated at 10 000 switching cycles typical. The device is silicon-free, which matters for potting and coating compatibility in some industrial environments.