The Schneider Electric A9P42740 is an Acti9 iC40 miniature circuit breaker (MCB) rated at 40 A with a B-curve trip characteristic, 3P+N poles, and a breaking capacity of 4500 A Icn at 400 V AC per EN/IEC 60898-1 and 6 kA Icu at 400 V AC per EN/IEC 60947-2.
The 40 A rated current (In) sets the continuous load this breaker can carry without tripping — sized for a 40 A distribution circuit feeding sub-panels, large fixed loads, or feeder protection. The 4.5 kA Icn (service breaking capacity per 60898-1) tells you the breaker can safely interrupt a fault up to 4.5 kA repeatedly — adequate for most domestic or light commercial distribution boards. The 6 kA Icu (ultimate breaking capacity per 60947-2) is the one-shot fault limit; if your available fault current exceeds 6 kA at the panel, you need a higher-rated breaker upstream or a current-limiting device. The 3P+N configuration protects three live poles with a switched neutral (left-side neutral position). The neutral pole is not protected — it switches but does not trip. The IP20 finger-safe terminals and IP40 modular enclosure mean it's suited for enclosed distribution boards, not washdown environments.
The 54 mm width (6 x 9 mm pitches) and 85 mm height fit standard modular enclosure grids. Tunnel terminals accept 1–16 mm² rigid or 1–10 mm² flexible wire; strip 14 mm and torque to 2 N·m. The toggle handle provides ON/OFF and trip indication — useful for quick visual status checks on the panel door.