The Schneider Electric MGN25121 is a C60H miniature circuit breaker from the Multi9 range, rated 40 A at 50 °C with a D tripping curve and 2 protected poles. It's built for distribution duty in 50/60 Hz AC networks, with a 30 kA Icu at 240 V AC phase-to-phase per EN/IEC 60947-2 — that's the short-circuit rating that decides if it holds on a hard fault without upstream damage.
Snaps onto 35 mm symmetrical DIN rail, fixed mounting, 4 module pitches wide (36 mm per pole, 72 mm total). Depth is 73 mm, height 81 mm — standard for the C60 family, so it drops into an existing Multi9 panel without re-spacing the gland plate. Tunnel terminals accept 1.5 to 35 mm² rigid or flexible, stripped 14 mm, torqued to 3.5 N.m. IP20 finger-safe front, pollution degree 3 rated for the enclosure environment.
Breaking capacity and service ratings
Rated Icu (ultimate breaking capacity) is 30 kA at 240 V AC, 15 kA at 415 V AC, and 10 kA at 440 V AC. The Ics (service breaking capacity) is 50% of those values — 15 kA, 7.5 kA, and 5 kA respectively — meaning after clearing a fault at that level the breaker is still usable, not welded shut. That's a real-world difference: on a 415 V distribution board with a 10 kA prospective fault current, this breaker clears it and stays in service.