What this MCB does on the rail
The Schneider Electric A9N21540 is a 32 A iDPN miniature circuit breaker from the Clario range, wired 1P+N for single-phase distribution boards. Curve B trips magnetically between 3 and 5 times rated current (96–160 A), so it catches short-circuit faults fast on resistive or lighting loads where inrush is low — think heater banks, general socket circuits, control transformers. The 4500 A Icn breaking capacity at 230 V AC (EN/IEC 60898-1) handles typical domestic and light commercial fault levels; if your panel sees higher prospective short-circuit current, you'd step up to a higher-rated MCB or add a backup fuse upstream.
Clip-on mount to standard DIN rail, 18 mm width (2 x 9 mm pitches) — one module wide, so it slots into a crowded enclosure without eating up spare ways. Neutral on the left, tunnel terminals accept 0.33–16 mm² rigid or 0.33–10 mm² flexible; strip 13 mm, torque to 2 N·m. IP20 finger-safe front, but the back and terminals are live when installed — panel builders treat this as a standard enclosed MCB, not a sealed unit for washdown zones.
Curve B means the magnetic release acts at 3–5× In — lower than Curve C (5–10× In) — so it's a better match for circuits without motor or transformer inrush. The 4500 A breaking capacity at 230 V AC is the Icn per EN 60898-1; that's the rated short-circuit capacity the breaker can clear without damage. Pollution degree 3 (IEC 60947-1) means it's rated for conductive environments typical of distribution panels — no special coating needed for normal indoor use. Tropicalisation class 2 per IEC 60068-1 covers 95 % RH at 55 °C, so it holds up in humid plant rooms or coastal sites without derating.