The Schneider Electric A9R91240 is an Acti9 iID 2-pole residual current circuit breaker (RCCB) rated for 40 A continuous current with a 30 mA earth-leakage sensitivity — the standard threshold for personal protection against direct contact in residential and light commercial panels. It's a voltage-independent, instantaneous-trip device, so it doesn't need a separate power supply to detect leakage; the fault current itself drives the mechanism. That Type A-SI (Super Immunised) classification means it handles pulsed DC fault currents from electronics (VFDs, LED drivers, UPS) without nuisance tripping from high-frequency leakage that would fire a standard Type A.
The 40 A rated current (In) sets the maximum load this RCCB can carry continuously — sized for a main incomer or sub-feed on a 40 A circuit. The 30 mA sensitivity is the IEC touch-protection standard; it clears a ground fault before heart-fibrillation risk sets in. Type A-SI adds immunity to 8/20 µs surge currents up to 3000 A without tripping, so you don't lose the circuit when lightning or switching transients hit the earth path. Voltage-independent operation means it works even if the neutral-to-earth voltage collapses, which matters on TT or IT earthing systems where the fault loop impedance can be high.
Clip-on mounting to a standard 35 mm DIN rail — 4 module pitches (36 mm wide per pole, 72 mm total for 2P). Wire stripping length is 14 mm. IP20 finger-safe on the front face, IP40 inside a modular enclosure — standard for distribution board use.