The Schneider Electric A9N21571 is a Clario iDPN N miniature circuit breaker (MCB) rated 40 A with a D trip curve, designed for 1P+N distribution circuits on 230 V AC networks at 50/60 Hz. The D curve means the magnetic trip operates at 10 to 14 times the rated current (10...14 x In) — that's 400 to 560 A instantaneous trip threshold, sized for loads with high inrush like small motors, transformers, or lighting ballasts where a B or C curve would nuisance-trip on startup. The thermal-magnetic trip unit combines a bimetal strip for overload protection and a solenoid for short-circuit protection. The 1P+N configuration switches the phase and neutral; suitability-for-isolation is marked Yes.
Mounting, integration, and panel fit
Clip-on mounting on a DIN rail (35 mm symmetrical rail per EN 60715). The 18 mm width per pole (2 x 9 mm pitches) means this 1P+N unit occupies 18 mm of rail space — standard for a slim single-module MCB. Depth is 78 mm from the rail face to the front of the toggle, height 81 mm. The tunnel-type terminals accept 0.75 to 16 mm² rigid or 0.33 to 10 mm² flexible on both upstream and downstream sides; tightening torque is 2 N·m, wire strip length 13 mm. That terminal range covers everything from 1.5 mm² lighting circuits up to 10 mm² feeder tails.
Durability and environmental limits
Rated for 10,000 electrical cycles and 20,000 mechanical cycles under rated load — that's roughly 27 years of one operation per day on the mechanical side, or 13 years on the electrical side. Operating altitude is limited to 2000 m; above that, the air density drop reduces dielectric strength and cooling, so derating applies.