The Siemens SENTRON 5SM3315-0KK is a 2-pole residual current circuit breaker (RCCB), type AC, rated 125 A with 30 mA trip sensitivity on 230 V AC. That 30 mA threshold catches ground-fault leakage before it becomes a shock hazard — standard for personnel protection in residential and light commercial distribution boards. The 10 kA short-circuit current rating (SCCR) means it safely interrupts faults up to that level without cascading upstream, sized for typical utility-side fault capacity.
Snaps onto DIN rail (REG profile), occupies 2 modular width units (36 mm at 18 mm/module), and installs in any orientation. The 70 mm installation depth fits standard 85 mm deep enclosures with room for wiring. Supply can enter from top or bottom — no forced busbar orientation. IP20 only once the distribution board is closed and conductors are connected; treat it as a panel-internal device, not for wet or dusty environments.
Ambient operating range is -5 °C to 45 °C; storage range extends to -40 °C. The 10,000 mechanical cycles typical service life is standard for a residual current device in this class — not a daily-switching contactor, but fine for the occasional test-button exercise and fault clearing it sees in service. Silicon-free construction matters for environments where silicone outgassing can contaminate contacts or optics. Overvoltage category III means it's rated for fixed-installation level (distribution board, not downstream socket).