The Siemens SENTRON 5SL6125-6BB is a 1-pole miniature circuit breaker (MCB) with a B tripping characteristic, rated 25 A at 400 V AC. It breaks fault currents up to 6 kA per both EN 60898 and IEC 60947-2 — that's the standard interrupting rating for residential and light commercial distribution boards, meaning it clears a short-circuit without upstream device intervention as long as the prospective fault current stays under that limit.
At 25 A it covers lighting circuits, socket outlets, and small appliance feeds. The 6 kA breaking capacity matches the typical domestic service entrance; if your panel's prospective short-circuit current exceeds that, you'd step up to a higher-rated SENTRON series (e.g., 5SY with 10 kA or 25 kA). Single-pole (1P) form factor occupies 1 modular width unit (18 mm) on DIN rail. Mounting position is unrestricted, and the 70 mm installation depth plus 76 mm overall depth fits standard 80 mm deep enclosures with room for wiring. The -40 °C to +75 °C storage range covers most unheated warehouses; the operating derating above +55 °C at 95% humidity is noted in the spec, so if the breaker lives in a hot attic or boiler room, you'll want to check the thermal curve.