The A9F05303 is a Schneider Electric Acti9 iC60N miniature circuit breaker rated 3 A with a D curve, meaning the magnetic trip threshold is 12 x In ±20 % — so it holds through motor inrush without nuisance tripping, then clears hard faults fast. The 50 kA Icu at 415 V AC (per EN/IEC 60947-2) gives headroom for high-fault panels; the same unit also carries a 6 kA Icn at 400 V under EN/IEC 60898-1 for residential or light commercial coordination. Three poles, thermal-magnetic trip, overvoltage category IV — sized for distribution boards where the upstream transformer is close. Snaps onto a DIN rail (6 x 9 mm pitches), 54 mm wide, 91 mm tall, 78.5 mm deep. Double terminals top and bottom accept 1–25 mm² rigid or 1–16 mm² flexible; wire strip length 14 mm, torque to 2 N·m.
D-curve selectivity and the so-what
The D curve (12 x In magnetic trip) is the key differentiator from a C curve (5–10 x In) or B curve (3–5 x In). For a 3 A MCB, that means the magnetic release fires between 28.8 A and 43.2 A — high enough to pass the starting surge of a small motor or transformer, low enough to protect the downstream cable. If your BOM calls for a D-curve 3 A MCB, swapping in a C curve risks nuisance trips on every start; swapping in a B curve risks the same plus inadequate short-circuit protection for the load.
Dual-certified to EN/IEC 60947-2 (industrial) and EN/IEC 60898-1 (residential/ commercial). Pollution degree 3, suitability for isolation marked on both standards. Separate earth-leakage block available if needed.