What this RCCB is and what it does
The Siemens 5SM3645-6 is a 4-pole residual current circuit breaker (RCCB) from the SENTRON family, rated 125 A with a 300 mA residual trip threshold, type A, for 400 V AC 50 Hz networks. It is an instantaneous (non-time-delayed) device, meaning it trips without intentional delay on a ground fault — suited for general distribution where selectivity with downstream RCDs is not required. The 10 kA short-circuit current rating (SCCR) per EN 60898 and IEC 61008-1 means the device can safely interrupt a fault up to 10 kA without external backup fusing, though the 1.25 kA rated conditional short-circuit capacity (also per both standards) is the value to coordinate with upstream protection for selectivity studies.
Mounting and panel integration
Snaps onto DIN rail (REG) and occupies 4 modular width units (72 mm wide). Installation depth is 70 mm; overall depth 77 mm. Mounting position is unrestricted — vertical or horizontal in the enclosure. Supply can enter from top or bottom. The IP20 rating applies only when the distribution board is installed and conductors are connected — normal for a panelboard interior.
Environmental and mechanical notes
Operating temperature range -25 °C to +45 °C; storage down to -40 °C. Silicon-free construction. Mechanical service life 10 000 operating cycles typical. Supplementary devices (e.g. auxiliary switches, shunt trips) can be installed on the side.