The A9N18549 is a 4-pole add-on residual current device from the Acti9 Vigi C120 range, rated 125 A with a 1000 mA earth-leakage sensitivity.
The 125 A rated current (In) sets the continuous load this RCD can carry without derating — sized for a main feeder or large sub-feed in a 230...415 V AC network. The 1000 mA sensitivity is selective (time-delayed), meaning it coordinates with downstream 30 mA or 300 mA RCDs so that a fault on a branch trips the branch device first, not this upstream unit. That selectivity is critical in a distribution board where you want nuisance-free coordination. Type AC earth-leakage protection covers sinusoidal AC residual currents only — standard for general-purpose circuits without electronic loads that generate pulsed or DC fault currents. The voltage-independent tripping technology means the RCD operates even if the supply neutral is lost, a reliability feature for safety continuity.
Clip-on mounting on 35 mm DIN rail, 4-pole wide at 198 mm (10 x 9 mm pitches). Tunnel terminals accept 1...50 mm² rigid or 1...35 mm² flexible cable; tighten to 3.5 N.m. Strip 15 mm of insulation. IP20 finger-safe terminals — standard for enclosed distribution boards.