It is the companion RCD for the 5SY series MCBs, combining overcurrent protection in the MCB with earth-leakage detection here. Rated 40 A at AC with a 30 mA Type A trip characteristic, it detects sinusoidal AC residual currents plus pulsating DC — covering the common fault modes in single-phase circuits feeding electronics, VFDs, or switched-mode supplies. Short-time delayed design (letter G / short-delay per IEC 60755) means it withstands brief surge currents without nuisance tripping — rated surge current resistance is 3 kA. That matters when a capacitor bank or a nearby lightning surge hits the line; the RCD holds in rather than dropping a critical circuit. The delay is fixed — not adjustable — so it coordinates with upstream selective RCDs in a graded protection scheme.
DIN-rail footprint and panel integration
Mounting position any; supply can enter from top or bottom. IP20 with connected conductors and installed in a distribution board — meaning it is rated for dry indoor enclosures only, not washdown or outdoor exposure. The REG fastening method clips onto the rail; no tools needed for installation or removal.
Thermal derating — don't just read the 40 A label
Above that, the continuous current must be reduced: 37.2 A at 45 °C, 36 A at 50 °C, 34.8 A at 55 °C, 34 A at 60 °C, 33.2 A at 65 °C, and 32 A at 70 °C. If the distribution board runs hot — common in a crowded enclosure or next to a transformer — size the upstream breaker for the derated figure, not the nameplate 40 A.
The 5SM2322-6KK01 is a standard catalogue item in the SENTRON range.