The Siemens 5SL4303-6 is a SENTRON miniature circuit breaker (MCB) — 3-pole, B-curve, rated 3 A at 400 V AC, with a 10 kA breaking capacity per EN 60898. It's designed for residential and infrastructure branch-circuit protection where the B characteristic (trips at 3–5× In) handles lighting and general-purpose loads without nuisance tripping from inrush.
Rated current derates with ambient temperature: 2.88 A at 30 °C, 2.82 A at 45 °C, 2.69 A at 55 °C. If the panel runs hot, factor that into the load schedule. Mechanical endurance is 10,000 switching cycles typical — enough for routine isolation but not for frequent motor starting. Operating temperature range -40 to 75 °C covers unheated utility rooms and outdoor-adjacent enclosures.