It provides earth-leakage protection for the downstream circuit without replacing the existing MCB — a modular approach that keeps the breaker's overcurrent and short-circuit ratings intact while adding the RCD function. Rated 25 A continuous current with 300 mA Type A earth-leakage sensitivity, it trips instantaneously on fault and is voltage independent, meaning it operates even if the supply voltage collapses during a ground fault.
The 300 mA sensitivity is a common choice for group incomer or sub-distribution protection where nuisance tripping from normal leakage (cable capacitance, filter Y-caps) must be avoided. The instantaneous trip characteristic means no intentional time delay; the RCD clears within 200 ms per EN/IEC 61009-2-1, which is the standard for this class. Voltage-independent tripping is a reliability advantage: the RCD stores enough energy from the fault current itself to open the contacts, so a lost neutral or sagging supply won't disable protection.
The device occupies 2 x 9 mm pitches (18 mm width), matching the 1P+N module footprint. It connects to the upstream MCB via screw terminals — tunnel-type terminals accepting 1–16 mm² rigid or 1–10 mm² flexible conductors, tightened to 2 N·m. A fault-indication flag provides local visual status.