What it is and what it does
The Siemens 5SM3647-6 is a 4-pole residual current circuit breaker (RCCB) from the SENTRON family, rated 80 A at 40°C and 400 V AC on a 50 Hz network. It detects sinusoidal AC and pulsating DC fault currents (Type A), which covers most modern electronic loads — switched-mode power supplies, variable-speed drives, and appliances with rectifier front ends. The instantaneous (short-time delayed) design means it trips without intentional delay, so it's suited for circuits where nuisance tripping from transient leakage is not expected.
Mounting and integration
Snaps onto a DIN rail (REG profile) and occupies 4 width units (72 mm wide). The 77 mm depth and 70 mm installation depth fit standard distribution boards — no deep enclosure needed. Mounting position is any orientation, which simplifies layout in tight panels. Terminal capacity accepts solid or stranded conductors from 1.5 mm² up to 25 mm², covering most branch-circuit and sub-feed sizes. IP20 rating with connected conductors means it's protected against finger contact once installed inside an enclosure.
Thermal derating and short-circuit coordination
The 80 A rating holds up to 45°C ambient; above that it derates linearly to 64 A at 70°C. For panels near heat sources or in warm environments, check the actual ambient against the 40°C baseline. The short-circuit current rating is stated as 0 kA — this RCCB is not designed to interrupt fault currents on its own; it must be paired with an upstream overcurrent protective device (MCB or fuse) that clears the fault. The permissible I²t value of 70,000 A²·s gives a coordination target for the upstream breaker. Surge current resistance is 1 kA, meaning it withstands lightning-induced or switching transients without nuisance tripping.