The Siemens 5SY7240-8 is a 2-pole SENTRON miniature circuit breaker rated 40 A with a D tripping characteristic, designed to protect branch circuits against overcurrent and short circuits in industrial control panels and distribution boards. The D curve means it tolerates high inrush currents — typical for motor, transformer, or welding loads — without nuisance tripping, while still clearing faults at 15 kA per EN 60898 or 20 kA per IEC 60947-2. It snaps onto a DIN rail (2 modular width units, 36 mm wide) and mounts in any position, with a depth of 76 mm and an installation depth of 70 mm, so it fits standard enclosures without extra clearance.
Ratings and derating — what they mean on the panel
At 35 °C ambient the breaker carries the full 40 A; at 40 °C it derates to 37.56 A, at 50 °C to 34.96 A, and at 60 °C to 32.16 A — so if the panel runs hot, size the upstream protection for the derated value, not the nameplate.
Certified to IEC/EN 60898-1, IEC/EN 60947-2, and UL 1077, with a halogen-free, silicon-free design. Compliance documentation (RoHS, REACH) is available with the shipment.