The Schneider Electric A9Y84325 is an add-on residual current device (RCD) from the Acti9 Vigi iC40 range, designed to clip onto the outgoing side of a compatible Acti9 iC40 miniature circuit breaker (MCB) via screws. It adds earth-leakage protection to the circuit, tripping instantaneously when it detects a fault current of 30 mA or more. The 30 mA sensitivity is the standard threshold for personal protection against electric shock in residential and commercial final circuits — it catches leakage through the human body before fibrillation becomes likely. The Type A-SI (Super Immunised) classification means it handles pulsed DC fault currents (from electronics like rectifiers or VFDs) without nuisance tripping from high-frequency leakage, while still tripping on sinusoidal AC and pulsating DC faults. Rated operational voltage is 400 V AC on a 3-pole (3P) network at 50/60 Hz, making it a direct fit for three-phase outgoing circuits in distribution boards. Rated current is 25 A, so it pairs with a 25 A MCB in the same busbar slot. The device is voltage-independent for tripping — it does not need a separate power supply to detect leakage, which simplifies wiring and keeps it functional even if the line voltage drops.
Clip-on mounting on a DIN rail — 4 modules wide at 9 mm per pitch, so it occupies 36 mm of rail space. Dimensions are 90 mm wide, 99.5 mm high, 74 mm deep. The 74 mm depth is the key clearance dimension when the front cover of the distribution board closes; check that the door or trim clears this plus the MCB it attaches to. Tunnel-type terminals on the bottom accept 1 to 16 mm² rigid or 1 to 10 mm² flexible cable; strip 14 mm for the connection.