The A9N18559 is an add-on residual current device (RCD) from the Schneider Electric Acti9 Vigi C120 range. It is a 3-pole (3P) block rated at 125 A, designed to clip onto a compatible MCB (miniature circuit breaker) via screws, providing earth-leakage protection for outgoing circuits in a distribution board. Its 1000 mA sensitivity and Type A-SI (Super Immunised) classification mean it handles high-leakage industrial loads and is immune to nuisance tripping from transient surges or DC components — a common requirement on variable-speed drive or UPS-fed circuits.
Rated at 125 A continuous and 230...415 V AC 50 Hz, this block sits at the incomer or large subfeed position — think main switchboard feeders or high-current distribution. The 1000 mA earth-leakage threshold is deliberately high; it's not for personnel protection (that needs 30 mA) but for equipment and fire protection on circuits where normal leakage from filters and drives already runs tens of milliamps. Selective time delay (marked S) means it coordinates with downstream 30 mA RCDs — the downstream trips first, the upstream block holds off, keeping the rest of the board live. Voltage-independent tripping means it will clear a fault even if the neutral is lost — a safety net for IT or corner-grounded delta systems. Mechanical durability is rated at 20000 cycles — that's a maintenance interval, not a design life for frequent switching. This is a protective device, not a daily disconnect switch.
Clip-on mounting onto a 35 mm symmetrical DIN rail, occupying 10 pitches of 9 mm (171 mm width). Tunnel terminals accept 1...50 mm² rigid or 1...35 mm² flexible cable, with stripping length of 15 mm and tightening torque of 3.5 N.m.
Designed to EN 61009 and IEC/EN 61009-2-1, with pollution degree 3 per IEC 60947-2 and a rated impulse withstand voltage of 6 kV.