The Siemens 5SM3647-6KL is a 4-pole residual current circuit breaker (RCCB) from the SENTRON family, rated for 80 A at 400 V AC with a 300 mA Type A residual trip. Type A means it detects pulsating DC fault currents on top of standard AC sine-wave leakage — the kind you get from single-phase rectifiers in VFDs, switching power supplies, or LED drivers. That 300 mA threshold is a high-leakage trip point, typically specified for feeder or submain protection where nuisance tripping from normal equipment leakage needs to be avoided, not for final-circuit personnel protection (which usually calls for 30 mA). It's an instantaneous design (no short-time delay), so it clears fast on fault.
Snaps onto DIN rail (REG profile) and occupies 4 width units at 72 mm wide. The N pole is on the left side of the device (N left variant). Screw terminals accept 2.5 to 3 N·m tightening torque.