The Siemens 5SL4340-8 is a SENTRON miniature circuit breaker (MCB) — 3-pole, D-tripping characteristic, rated 40 A at 400 V AC, with a 10 kA breaking capacity certified to both EN 60898 and IEC 60947-2. That dual-standard rating means it covers residential/infrastructure panelboards (EN 60898) and industrial feeder circuits (IEC 60947-2) under one order code, simplifying your BOM for mixed-duty panels. D-curve tripping (10–20× In) is the right choice for transformer inrush, motor starting, or any load with a high short-duration surge — the magnetic trip holds off nuisance trips while still clearing a hard fault within the 10 kA SCCR. At 40 A this MCB handles a 15–20 kW three-phase motor or a lighting/distribution subfeed. Rated current derates with ambient temperature: 40 A at 30 °C, 37.89 A at 40 °C, 36.8 A at 45 °C, 34.47 A at 55 °C. In a warm enclosure (say 45 °C internal) the effective continuous rating drops to 36.8 A — size your upstream protection accordingly.
IP20 with conductors connected — fine for enclosed panels, not for wet-area standalone use. Mounting position any, so it can be installed horizontally or vertically inside a cabinet without derating. Overvoltage category III (distribution-level), pollution degree 2 (normal industrial/ commercial environment). Sealable terminals available — required for utility-metering or revenue-grade panels where tamper evidence is mandatory. Mechanical life 10 000 switching cycles typical — adequate for a protection device that operates infrequently (fault clearing or manual isolation), not a daily-switched load-break device.
Selectivity & Coordination
Energy limitation class 3 means this MCB limits let-through energy enough to coordinate with downstream branch breakers in most residential and light-commercial panelboards. The 5SL4340-8 is a 3-pole device switching all phases — it breaks all three poles simultaneously on a fault on any phase, which is standard for three-phase subfeeds and motor circuits. Do not use it for single-phase branch protection unless you are comfortable with an unswitched neutral.