The Schneider Electric A9N18457 is a miniature circuit-breaker from the Acti9 C120 range, rated 80 A at 30 °C with a C-curve trip characteristic (5–10 × In) and two protected poles, neutral on the left. Out here in the panel, it handles motor and distribution loads without the nuisance trips a B-curve would throw on a compressor start. Breaking capacity hits 15 kA Icn under EN/IEC 60898-1 at 400 V, and up to 30 kA Icu under EN/IEC 60947-2 at 240 V — enough for most light commercial panels. It's class 3 limitation, so let-through energy stays low during a short-circuit event.
Mounting and wiring realities
Clips onto 35 mm symmetrical DIN rail, occupies 6 module pitches (54 mm wide). Terminals accept up to 50 mm² rigid or 35 mm² flexible, tunnel type. IP20 finger-safe for the panel face, but don't spray it with washdown — that's not its job.