The Schneider Electric A9L20400 is an Acti9 iPRD20 Type 2 surge arrester — a 4-pole (4P) MOV-based unit rated for 230/400 V AC (+/- 10 %) at 50/60 Hz, with a maximum continuous operating voltage (Uc) of 350 V L/PE and N/PE. The 20 kA maximum discharge current (common mode L/PE and N/PE) and 5 kA nominal discharge current define its energy-handling capacity for distribution-network surge events.
The 72 mm width (8 x 9 mm pitches) and 85 mm height fit a standard DIN-rail enclosure slot — plan for 8 TE in the panel layout. Tunnel-type terminals on both top and bottom accept 2.5 to 35 mm² conductors; tighten to 2.5 N·m. The unit is rated for TN-C-S earthing systems, so verify your system configuration before mounting. The Type 2 classification (per EN 61643-11:2012 and IEC 61643-11:2011) means it is designed for the main distribution board to clamp switching and indirect lightning surges — not for direct-strike primary protection. The <1.1 kV voltage protection level (Up) tells you the let-through voltage the downstream equipment sees; pair it with an upstream disconnector (the evidence lists compatible IC60N/H/L or NG125H/L breakers, or gG fuses) to ensure fault coordination.