Merlin Gerin Multi 9 Ic 2000 P Manual Access

The sensor may be in a permanent shadow or dirty.

Unlike modern electronic RCDs, the Multi 9 IC2000 P (depending on the exact vintage) may be sensitive to line/load reversal. The manual explicitly marks "Line" on top and "Load" on the bottom. Reversing these can destroy the device during a fault. Merlin Gerin Multi 9 Ic 2000 P Manual

Increase the lux threshold or check the sensor placement. The sensor may be in a permanent shadow or dirty

Merlin Gerin Multi 9 IC2000P (often replaced by the newer Schneider Electric Acti9 IC2000P+ Merlin Gerin Multi 9 Ic 2000 P Manual