The Schneider Electric A9Y75740 is an add-on residual current device (RCD) from the Acti9 Vigi iCG40 range, designed to clip onto the outgoing side of a compatible Acti9 MCB. It provides earth-leakage protection for a 3P+N circuit, rated at 40 A with 300 mA sensitivity, Type A-SI (Super Immunised) — meaning it handles pulsed DC residual currents and resists nuisance tripping from high-frequency harmonics or transient surges common on modern electronic loads.
Rated operational voltage is 400 V AC at 50/60 Hz, with an insulation voltage of 440 V AC and impulse withstand of 4 kV — all conforming to EN/IEC 61009-2-1. That 4 kV impulse rating means it can handle switching transients and indirect lightning surges without flashover, critical for group incomer positions in distribution boards. The 300 mA sensitivity is instantaneous (no intentional time delay), so it trips as soon as the leakage exceeds that threshold. Type A-SI (Super Immunised) adds immunity to high-frequency currents up to 1 kHz, making it suitable for circuits with variable-speed drives, UPS systems, or LED lighting where standard Type A RCDs might false-trip. Mechanical durability is rated at 20,000 cycles, electrical at 10,000 cycles — figures that align with typical commercial and light industrial panel duty where the RCD is not switched daily under load.
Clip-on mounting to DIN rail, 9 mm pitches occupied: 6 (108 mm width). The device is an add-on that screws directly to the load side of an Acti9 MCB — no additional wiring between the MCB and RCD. Neutral is on the left, poles 3P + N. Tunnel-type terminals accept 1…16 mm² rigid or 1…10 mm² flexible on top; wire stripping length is 14 mm for top connection. Tightening torque: 2 N·m. IP20 on the device body, IP40 within a modular enclosure — standard for distribution boards inside a dry environment. Pollution degree 3 per EN/IEC 61009-2-1, meaning it tolerates conductive pollution (condensation, light dust) typical of industrial panels not hermetically sealed.