The Siemens 5SN6104-8CP is a SENTRON miniature circuit breaker (MCB) — a single-pole thermal-magnetic breaker rated for 400 V AC at 50 Hz, with a breaking capacity of 6 kA per EN 60898 and 30 kA per IEC 60947-2. That dual rating means it's certified for residential/infrastructure branch circuits (EN 60898) and also for industrial panel protection where higher fault currents are expected (IEC 60947-2).
That 18 mm width is the standard for single-pole MCBs — it slots into any SENTRON distribution board or industrial enclosure without crowding adjacent breakers. Accepts solid conductors up to 35 mm², so it handles the feed-through wiring for sub-distribution without needing a separate terminal block.
The 30 kA under IEC 60947-2 is the industrial rating, which tells you this breaker can interrupt a fault on a 400 V bus with high prospective short-circuit current without welding its contacts. That's the number that governs whether it coordinates with an upstream molded-case breaker. Mechanical life of 10 000 cycles is typical for an MCB — it's not a contactor for frequent switching, but it handles occasional manual isolation and fault clearing without issue.