The Schneider Electric A9N21538 is a Clario iDPN miniature circuit-breaker (MCB) — a 1P+N, 20 A, Curve B device rated to EN/IEC 60898-1. The thermal-magnetic trip unit handles overloads and short-circuits;
Rated 20 A continuous — sized for a 4.6 kW resistive load at 230 V single-phase. Curve B (3–5 × In) is the tightest magnetic trip band — it clears a short-circuit faster than Curve C or D, but it also means it may nuisance-trip on motor or transformer inrush. Use it for general-purpose distribution, lighting, and resistive loads where you want the fastest fault clearance. 1P+N construction switches the phase and switches the neutral through the same mechanism, but the neutral pole is not overcurrent-protected — it's a switched neutral. That's fine for single-phase final circuits where the neutral is bonded at the source.
Occupies one module width in a distribution board.