What it is and what it does
The Siemens 5SM9646-6 is a SENTRON residual current (RC) unit — an electronic RCD module designed to pair with a 5SL4 miniature circuit breaker. It's a 4-pole, Type A device rated for 63 A continuous current and 300 mA residual tripping current at 230/400 V AC, 50 Hz. Type A means it detects sinusoidal AC fault currents plus pulsating DC fault currents up to 6 mA smooth DC — the standard for circuits with single-phase rectifiers, switched-mode power supplies, or variable-speed drives that can produce pulsating DC leakage.
Mounting and panel fit
Snaps onto standard DIN rail (EN 60715) in any mounting position. The unit occupies 3 width units (54 mm) and has a 70 mm installation depth — same as a standard MCB, so it fits existing distribution boards without extra enclosure depth. IP20 rated with conductors connected, meaning it's protected against solid objects over 12 mm but not water ingress; mount inside a distribution board with a cover for any wet-area install.
Wiring and terminations
Terminals accept solid conductors from 0.75 mm² up to 35 mm² and stranded from 0.75 mm² to 25 mm². Tightening torque is 2.5 to 3 N·m — treat it like a standard 35 mm² terminal block. The power supply connects at the top, above the miniature circuit breaker, which is the conventional feed-side arrangement for RCBO assemblies.
Environmental and mechanical
Rated for ambient temperatures from -25 °C to +55 °C during operation, and can sit in storage from -40 °C to +75 °C. Mechanical service life is 10,000 switching cycles typical — that's the mechanism endurance, not the electrical breaking capacity. Surge current resistance is 3 kA, which covers most residential and light commercial transient events. Silicon-free construction, which matters for potting or conformal-coating compatibility in sensitive electronics environments.