The A9N18548 is an add-on residual current device (RCD) from the Acti9 Vigi C120 range, designed to bolt onto the outgoing side of a compatible Acti9 MCB via screw terminals. At 125 A rated current and 300 mA selective earth-leakage sensitivity, it sits at the high end of the Vigi C120 family — sized for a main incomer or a large subfeed in a 230…415 V AC 50/60 Hz network. The selective time delay means it coordinates with downstream RCDs: it holds during a fault long enough for the closer device to clear, so only the faulted branch trips. That selectivity is critical in a distribution board feeding multiple sub-circuits where nuisance tripping of the main switch would take the whole panel down. The 4P (four-pole) construction switches all live conductors — three phases plus neutral — which is required for a three-phase outgoing group where the neutral must be disconnected and reclosed with the phases. Voltage-independent tripping technology means the RCD operates without needing an external power supply; the fault energy itself drives the mechanism, so protection holds even if the neutral is lost upstream. The 198 mm width (10 x 9 mm pitches) occupies ten modular spaces — plan the DIN-rail layout accordingly.
The device is certified to EN 61009 and IEC/EN 61009-2-1, the harmonised standard for residual-current-operated circuit-breakers with integral overcurrent protection (RCBOs) — though this is an add-on RCD, not a combined unit.