Siemens 5SY4140-6 — B-curve 40 A MCB, dual-standard breaking capacity
The Siemens 5SY4140-6 is a 1-pole miniature circuit breaker from the SENTRON 5SY4 series, rated 40 A with a B-curve trip characteristic. It carries a 10 kA breaking capacity per IEC/EN 60898-1 and a 15 kA rating per IEC 60947-2 / UL1077, so it covers both residential-distribution board specs and industrial panel SCCR requirements under a single order code. The B-curve (3–5× In magnetic trip) means it is sized for resistive and general-purpose loads — lighting, small heaters, control transformers — not motor starting or high-inrush circuits where a C- or D-curve would be needed. At 40 A it is a common feeder or submain breaker in a 1-MW (18 mm) footprint.
Temperature derating — what the 40 A rating actually delivers
The 40 A rating holds at 35 °C ambient. Above that it derates linearly: 37.56 A at 40 °C, 36.28 A at 45 °C, 34.96 A at 50 °C, 33.6 A at 55 °C, and 32.16 A at 60 °C. If the panel ambient runs at 50 °C, plan for a 35 A continuous load, not 40 A.
Dual-standard breaking capacity — panel vs. distribution board
Rated 10 kA under IEC/EN 60898-1 (the standard for household and similar installations) and 15 kA under IEC 60947-2 / UL1077 (industrial control-panel standard). The higher 15 kA figure is the one that matters for an industrial panel SCCR calculation — it gives headroom over the 10 kA typical available fault current in most plant distribution boards.
Panel fit — 1 MW wide, 76 mm deep, any mounting position
Occupies a single modular width (18 mm) on DIN rail, with a depth of 76 mm (70 mm installation depth). The quick-assembly fastening system snaps onto the rail without tools. Mounting position is unrestricted — vertical, horizontal, or flat — which simplifies layout in crowded enclosures. IP20 with conductors connected; pollution degree 3 and overvoltage category III suit it for industrial control panels, not just clean distribution boards.
Compliance and approvals
Certified to IEC/EN 60898-1 and IEC 60947-2 / UL1077. Halogen-free and silicon-free construction. Energy limitation class 3. Sealable terminals (top and bottom combined terminals) allow tamper-proofing in metered or safety-critical circuits. The surrounding temperature influence spec (max 95% RH to 55 °C, derating above) is standard for this class.