What it is and what the ratings mean
The Siemens SENTRON 5SM3312-0 is a 2-pole residual current circuit breaker (RCCB) rated 25 A at 40 °C with a 30 mA trip threshold, designed for AC residual current detection. The 30 mA trip is the standard for personal protection against direct contact in residential and commercial final circuits — it catches leakage through the human body before fibrillation risk. The 10 kA short-circuit current rating (SCCR) means the device can safely interrupt a fault up to 10 kA at the rated voltage without welding contacts or rupturing the enclosure; that's the figure the panel designer uses for fault coordination with the upstream overcurrent device. Rated supply voltage is 230 V AC at 50 Hz, which covers standard single-phase residential and light commercial mains in Europe and many other regions. The instantaneous design (no intentional delay) trips within milliseconds of the residual current exceeding 30 mA — no time grading for selectivity, so it's the last device in the chain, not a delayed S-type for feeder protection.
Mounting and integration
Snaps onto DIN rail (REG) and occupies 2 modular width units (36 mm total). Depth is 70 mm, which matches the standard 70 mm installation depth for SENTRON distribution boards — no extra clearance needed behind the panel door. Mounting position is any orientation, so it fits in tight enclosures where vertical or horizontal rail placement is forced. The IP20 rating applies only when the distribution board is installed with connected conductors; treat it as protected-finger-safe inside a closed panel, not for wet or dusty environments. Supply cord can enter from top or bottom — no forced orientation for line/load. Silicon-free construction matters if the panel is in a painting or coating line where silicone outgassing causes adhesion defects.