What this RCD does in the panel
The Schneider Electric A9N18544 is an add-on residual current device (RCD) from the Acti9 Vigi C120 range, designed to clip onto the outgoing side of a compatible Acti9 MCB. It provides earth-leakage protection for circuits rated up to 125 A on 230…415 V AC networks at 50/60 Hz. The 300 mA sensitivity with selective time delay means it's intended for feeder or submain circuits where a small delay before tripping is needed to coordinate with downstream RCDs — preventing a nuisance trip on a ground fault that a downstream device should clear first. Type AC protection covers sinusoidal alternating residual currents. The voltage-independent tripping technology means it operates without needing a separate power supply — it uses the fault current itself to trip, so it remains functional even if the line voltage drops.
The 2-pole (2P) form factor occupies 7 modules of 9 mm pitch (63 mm total width), with a depth of 73 mm and height of 95 mm. Tunnel-type terminals accept 1…50 mm² rigid or 1…35 mm² flexible conductors; tighten to 3.5 N·m after stripping 15 mm of insulation. Rated for pollution degree 3 (industrial environments) per IEC 60947-2, with IP20 finger-safe protection on the front. Ambient operating range is -5…60 °C; storage range -40…60 °C.