Panel fit and ratings for the BOM
The Siemens SENTRON 5SY4240-8CC is a 2-pole miniature circuit breaker (MCB) with a D tripping characteristic, rated 40 A at 35 °C ambient and 440 V AC multi-phase. At 40 °C the continuous rating drops to 37.6 A, at 50 °C to 35.04 A, and at 55 °C to 33.68 A — the thermal derating curve is published, so you can size it for a warm enclosure without guessing.
Integration and compliance notes
The breaker is designed for mechanical engineering and industrial applications. It is sealable, halogen-free, silicon-free, and carries touch protection on the terminals. The part is function-group F per EN 61346-2 and IEC 81346-2, which maps to the protective-device symbol in schematics. No neutral conductor switching is provided; this is a line-side only pole configuration.