1-pole 40 A B-curve MCB for panel and railway duty
The Siemens SENTRON 5SY4140-6KK11 is a 1-pole miniature circuit breaker rated 40 A with a B tripping characteristic, designed for AC voltage systems. It occupies a single 18 mm modular width on the DIN rail and is rated for a breaking capacity of 10 kA per EN 60898 and 15 kA per IEC 60947-2, giving it headroom for high-fault utility connections or industrial sub-distribution. The part is designated for railway applications, with halogen-free and silicon-free construction, and carries IP20 protection with connected conductors.
What the ratings mean for fit
The 40 A rating at 35 °C is the nominal; derate to 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. In a warm panel — say 50 °C ambient — expect the breaker to carry 34.96 A continuously without tripping. The B-curve trips between 3 and 5 times rated current, so it is suited for resistive or lightly inductive loads (heating, lighting, small control transformers) rather than motor starting. The 10 kA (EN 60898) and 15 kA (IEC 60947-2) ratings mean it can safely interrupt faults at those levels; the IEC 60947-2 figure is the one to use for industrial panel SCCR calculations. Pollution degree 3 and overvoltage category III suit it for fixed installations in enclosures. Mounting position is any, and the quick-assembly fastening method clips onto the DIN rail without tools. The combined terminal top and bottom accept wiring from either direction. Depth is 76 mm, installation depth 70 mm, height 90 mm — fits standard distribution boards and sub-panels.