The Schneider Electric A9Y76740 is an add-on residual current device (RCD) from the Acti9 Vigi iCG40 range, designed to bolt onto the outgoing side of a compatible Acti9 MCB via the screw terminals. It provides earth-leakage protection for a 3P+N circuit at 40 A rated current and 400 V AC operational voltage. The 300 mA sensitivity is selective (time-delayed), so it coordinates with downstream 30 mA RCDs — the upstream unit holds off during a fault to let the closer device clear first, avoiding a whole-section blackout for a single branch fault.
Rated at 40 A (In) and 400 V AC, this RCD handles the full load current of a typical sub-distribution board feeding lighting, general-purpose sockets, or small motor circuits — not a main incomer for a whole building, but a group feeder. The Type A-SI (Super Immunised) classification means it rejects nuisance tripping from pulsed DC fault currents and high-frequency leakage common in VFD-driven loads, switched-mode power supplies, and electronic ballasts. Standard Type A RCDs can false-trip on those waveforms; the A-SI variant holds steady. Voltage-independent tripping (no need for an auxiliary supply) means the RCD clears a ground fault even if the line voltage collapses — critical for safety in a group incomer where a lost neutral could otherwise leave a fault undetected.
Clip-on DIN rail mounting, 108 mm wide (6 x 9 mm pitches), with a depth of 74 mm and height of 99.5 mm. Tunnel-type terminals accept 1…16 mm² rigid or 1…10 mm² flexible cable on top; strip length 14 mm, tighten to 2 N·m. The screw connection to the upstream MCB uses the same terminals — no pigtail or flying leads. Rated for ambient operation from -25 °C to 60 °C, storage from -40 °C to 85 °C, and up to 2000 m altitude.