Type 2 SPD for IT earthing systems — what the ratings mean
The Schneider Electric A9L20421 is an Acti9 iPRD20r Type 2 surge arrester with pluggable MOV cartridges, rated for 230/400 V AC (+/- 10 %) at 50/60 Hz and designed for IT earthing systems. The 20 kA common-mode maximum discharge current (L/PE and N/PE) tells you it can handle a direct lightning strike's residual energy after the main Type 1 stage — not the full stroke itself. The nominal discharge current of 5 kA (8/20 µs) is the rating that governs its daily life: every surge event up to that level the MOV absorbs without degrading its protection curve. The voltage protection level stays under 1.8 kV (common mode, type 2 N/PE), which means downstream equipment with 2.5 kV impulse withstand (IEC 60664-1 category III) sees a safe clamping voltage. The maximum continuous operating voltage (MCOV) is 460 V L/PE, so it won't cook itself on a 400 V phase-to-phase system even with nominal fluctuations.
DIN rail integration and panel fit
The 72 mm width occupies 4 module pitches (9 mm each, 8 pitches total per, so 72 mm). Depth of 69 mm and height of 85 mm mean it fits most distribution boards with a 100 mm deep enclosure. Tunnel-type terminals accept 2.5 to 25 mm² rigid or 4 to 16 mm² flexible (with or without ferrule), strip length 14 mm, tightening torque 3.5 N·m. The white RAL 9003 housing matches the Acti9 family aesthetic for commercial panel builds.
Designed to EN 61643-11:2012 and IEC 61643-11:2011 — the Type 2 test class for permanently connected AC power-circuit SPDs. The temporary overvoltage (TOV) withstand is 337 V L/N for 5 seconds; above that, the safe failure mode triggers at 1455 V L/PE or N/PE for 200 ms. Ground leakage current is 0.6 mA. Operating temperature range -25 to 60 °C, storage -40 to 85 °C, relative humidity 5–95 %. Remote signalling via a 1 C/O contact rated 0.25 A / 250 V AC.