The Siemens 5SL4640-8 is a SENTRON miniature circuit breaker (MCB) in the 5SL series, 4-pole (3P+N) with a D tripping characteristic. Rated 40 A at 30 °C and 400 V AC, it delivers a 10 kA breaking capacity under both EN 60898 and IEC 60947-2 — enough for residential and light commercial infrastructure panels where high inrush loads (transformers, motor starters) are present. The D-curve means it tolerates short-duration surges up to 10–20× rated current before tripping, so nuisance trips on startup are rare.
What the ratings mean for fit
The 40 A rating is at 30 °C ambient; at 40 °C it derates to 37.89 A, at 45 °C to 36.8 A, and at 55 °C to 34.47 A. If your panel runs warm — say, a crowded DIN-rail enclosure — size the upstream load accordingly. The 10 kA SCCR (both EN 60898 and IEC 60947-2) tells you this breaker safely interrupts a fault up to 10 kA at 400 V without welding contacts or cascading failure upstream. Overvoltage category III and pollution degree 2 confirm it's rated for fixed-installation mains distribution, not just downstream sub-circuits.
Mounting and integration
Occupies 4 modular width units (72 mm wide) on standard DIN rail. Installation depth is 70 mm; total depth 76 mm. Mounting position is unrestricted — horizontal, vertical, or upside-down on the rail — and the housing is sealable, halogen-free, and silicon-free. IP20 with connected conductors means it's protected against finger contact but not washdown; keep it inside a closed panel.