The Schneider Electric A9Y76640 is an Acti9 Vigi iCG40 add-on residual current device — a voltage-independent, 1P+N unit rated 40 A with 300 mA earth-leakage sensitivity. It clips onto the DIN rail alongside the corresponding MCB, connected by screws, and serves as a group incomer in a distribution board. The Type A-SI (Super Immunised) classification means it handles pulsed DC fault currents and resists nuisance tripping from upstream surge arrestors or variable-speed drives, which is the main reason you'd pick this over a standard Type A.
The 300 mA sensitivity is selective (time-delayed), so it coordinates with downstream 30 mA RCDs: the downstream unit trips first on a person-contact fault, while this one only clears on insulation faults or cumulative leakage. That selectivity saves you chasing a whole-board blackout when a single socket RCD trips. Voltage-independent tripping means the RCD operates even if the neutral is lost upstream — the fault energy itself powers the trip mechanism. That is a safety-relevant feature for group incomers where you cannot guarantee the supply voltage under fault conditions. Clip-on mounting on standard DIN rail, 2 x 9 mm pitches wide (18 mm). IP20 body, IP40 inside a modular enclosure — fine for dry indoor distribution boards, not for washdown areas.