The A9N21756 is a Clario-series Vigi DPNc add-on residual current device (RCD) from Schneider Electric, designed as a group incomer for final distribution boards. It provides earth-leakage protection for a 3P+N circuit at 25 A rated current and 300 mA sensitivity, Type AC (sinusoidal AC fault currents only), voltage-independent tripping, instantaneous response. The 400 V AC phase-to-phase operational voltage and 440 V rated insulation voltage suit standard 400/230 V three-phase networks at 50 Hz.
The 25 A rated current (In) and 300 mA sensitivity define the protection envelope: this block sits downstream of a 25 A MCB (or smaller) and will trip on leakage above 300 mA. Voltage-independent tripping means the RCD operates without needing a separate power supply; it uses the fault energy itself. The instantaneous time delay (no intentional delay) means it trips within 300 ms at rated residual current, per EN/IEC 61009-1.
Clip-on mounting to DIN rail, neutral on the left, 3P+N poles. The add-on block screws directly to the downstream MCB (by screws, per the spec). 54 mm wide, 82 mm tall, 70 mm deep — occupies a standard 3-module width on the rail. Terminals accept 0.75…16 mm² rigid or 0.33…10 mm² flexible cable; strip 13 mm, tighten to 2 N·m. The ON/OFF local signalling gives a visual trip indication. Tropicalisation class 2 (IEC 60068-1) means it withstands damp-heat cycling — relevant for non-air-conditioned plant rooms in humid climates.