The Schneider Electric A9N18579 is an Acti9 Vigi C120 add-on residual current device block — 4 poles, rated 125 A continuous, with a 300 mA Type A earth-leakage sensitivity. It clips onto a 35 mm symmetrical DIN rail and connects electrically to the companion MCB via screw terminals (tunnel type, accepting 1–50 mm² rigid or 1–35 mm² flexible). This is a voltage-independent residual current tripping block, meaning it detects leakage current without needing an external power supply to the electronics — the trip mechanism derives its energy from the fault current itself, which is a reliability advantage in installations where a loss of supply could otherwise blind an electronic RCD.
The 125 A rated current (In) sets the continuous load capacity — sized for high-current outgoing feeders or group incomers in a distribution board. Voltage-independent tripping means the block works regardless of whether the upstream MCB is closed; it does not rely on an auxiliary supply. The 4P configuration protects all poles (, L2, L3, N) simultaneously. The 6 kV impulse withstand voltage (Uimp) confirms it coordinates with standard distribution system surge levels.
Deployment context
The 9 mm pitch count of 10 (198 mm width total) tells you the panel fill factor — it occupies ten module positions on the rail. IP20 finger-safe terminals suit enclosed panels; no washdown rating. Mechanical durability of 20,000 cycles reflects the expected switching life under normal operation.
The A9N18579 carries an Active lifecycle status from Schneider Electric. It is a current-production part within the Acti9 range. For BOM-line commitment, the key fit criteria are the 125 A rating, 4P configuration, 300 mA Type A sensitivity, and voltage-independent tripping — confirm these match your existing Vigi C120 / Acti9 MCB companion device before ordering.