The Siemens 5SM2622-2 is a 2-pole selective residual-current device (RCD) from the SENTRON family, designed to mount on a DIN rail alongside a 5SY miniature circuit breaker. It is rated for 40 A at AC and trips at a 300 mA fault current — a combination used where you need earth-fault protection but want to avoid nuisance trips from normal leakage or transient surges on the line. The selective design (type S) means it delays tripping slightly, so a downstream RCD or RCBO clears a fault first. That makes the 5SM2622-2 a good fit for the incoming feed of a sub-distribution board where you want coordination — not the first device to trip on a ground fault.
Rated at 40 A continuous, this RCD handles the full load current of a typical lighting or general-purpose sub-feed. The 300 mA trip threshold is above the leakage of most hardwired equipment, so it won't drop out on cable capacitance or filter leakage — but it still provides personnel protection in industrial environments where 30 mA devices might nuisance-trip. Insulation voltage is rated at 460 V with a 4 kV surge withstand (overvoltage category III), so the unit is suitable for fixed-installation panels fed from the utility grid — not just final circuits. Pollution degree 2 means it expects a controlled environment inside the enclosure, which is standard for distribution boards.
It is designed as a companion to the 5SY MCB — the 5SM2622-2 clips alongside it and shares the same busbar footprint. Fastening method is standard rail-mount (REG). No sealable option — if your site requires lockable isolation, you'll need a separate lockout device on the upstream breaker.