What it is and what it does
The Siemens SENTRON 5SM3412-0 is a 2-pole residual current circuit breaker (RCCB) rated 25 A at 230 V AC, 50 Hz, with a 10 kA short-circuit current rating (SCCR). It's an instantaneous type for AC fault currents — meaning it trips without intentional delay on sinusoidal AC earth faults, which is the standard choice for general-purpose protection in residential and light commercial distribution boards.
Ratings and what they mean for fit
The 25 A rating holds at 40 °C and 45 °C ambient; derate to 23.5 A at 50 °C, 22 A at 55 °C, 20.5 A at 60 °C, 19 A at 65 °C, and 17.5 A at 70 °C. If your panel runs hot — say near a transformer or in a non-ventilated enclosure — you need to account for that derating curve, not just the nameplate 25 A. Mounts on DIN rail (REG), occupies 2 width units (36 mm wide), with a depth of 70 mm and height of 90 mm. Installation position is any orientation, and the supply can enter from top or bottom — handy when you're retrofitting into a crowded enclosure and can't re-route the busbar. IP20 rated with conductors connected and the distribution board installed — that's typical for enclosed panels, not for exposed or washdown locations. The housing is silicon-free, which matters if the panel is in a coating or potting environment where silicone outgassing can cause adhesion failures.
Lifecycle and sourcing
Lifecycle status is 'current'. This is a standard production part in the SENTRON 5SM3 family, sourced through normal Siemens distribution channels.