The A9N21760 is a Vigi DPNc add-on residual current device from Schneider Electric's Clario range — a voltage-independent, Type A RCD block that snaps onto the left side of a compatible MCB to provide earth-leakage protection for a 3P+N circuit. It is rated 25 A with 300 mA sensitivity, instantaneous trip, and is designed for 400 V AC phase-to-phase networks at 50 Hz.
The 25 A rated current (In) and 300 mA earth-leakage sensitivity are matched for group incomer or sub-distribution board protection where a higher leakage threshold is acceptable — typically for circuits feeding multiple loads where nuisance tripping from cumulative leakage is a concern. Type A detection covers pulsating DC residual currents, which standard AC-only RCDs miss; this matters for circuits with rectified loads like switching power supplies or variable-speed drives. The voltage-independent trip technology means the RCD operates without needing a separate power supply, so it clears leakage faults even if the line voltage collapses. The instantaneous time delay (no intentional delay) means it trips within the standard RCD response window — suitable for direct shock protection in final circuits, but coordination with downstream RCDs needs care to avoid nuisance tripping on transient leakage.
The add-on block screws directly to the MCB body — no extra wiring for the leakage detection circuit. Dimensions are 54 mm wide, 82 mm high, 70 mm deep, occupying six 9 mm pitches on the rail.