What it is and what it does
The Siemens 5SM3312-6KL is a 2-pole SENTRON residual current circuit breaker (RCCB), Type A, rated at 25 A and 30 mA trip sensitivity on a 230 V AC supply. The 30 mA trip threshold covers the standard for personnel protection — it clears ground faults before they reach a level that can cause ventricular fibrillation. Type A detection handles both sinusoidal AC residual currents and pulsed DC residual currents, which covers modern electronics and rectified loads. This is an instantaneous-trip design (no intentional time delay), so it reacts on the first half-cycle of a fault. The 10 kA short-circuit current rating (SCCR) means it can safely interrupt a fault current up to that level without welding contacts or rupturing the case — important when the device sits downstream of a higher-rated upstream breaker.
Panel fit and mounting
Snaps onto standard DIN rail (REG profile). The 36 mm width (2 modular units) and 70 mm depth let it slot into a standard distribution board without protruding past the gland plate. Mounting position is any orientation, and the supply can enter from top or bottom — no need to flip the rail for a specific feed direction. The N terminal is on the left side of the device, which is the arrangement you want when laying out a panel left-to-right: line in on the left, load out on the right. IP20 rating applies once the distribution board is installed with conductors connected — that's the standard for enclosed panel gear, not for standalone outdoor use. The terminals accept 1 mm² to 16 mm² conductors, covering most branch-circuit wiring from 1.5 mm² lighting circuits up to 6 mm² or 10 mm² feeder tails.