The Siemens 5SN6240-8CP is a SENTRON 5SN series miniature circuit breaker (MCB) — a 2-pole unit rated for 400 V AC at 50 Hz. That dual rating means you can spec it into either standard without swapping parts.
Two poles, 72 V DC maximum rating — so it handles DC control circuits up to that voltage, common in 48 V or 60 V DC bus applications. The 440 V AC maximum with multi-phase or single-phase operation means it's fine for 400 V three-phase panels and 230/240 V single-phase branch circuits. The 10 000 mechanical operating cycles typical service life is standard for an MCB in a panel that sees occasional switching; it's not a contactor for daily cycling. Dimensions: 36 mm wide (2 modular width units), 90 mm tall, 76 mm deep with a 70 mm installation depth. That's the standard 2-module footprint — drops into any 35 mm DIN rail enclosure without crowding adjacent breakers. Accepts solid conductors up to 35 mm², so it'll take the incoming feed from a main switch or busbar without needing a reducer.