Rated for the panel — 40 A C-curve, 2-pole, 10 kA
The Siemens 5SY4240-7CC is a 2-pole miniature circuit breaker from the SENTRON family, rated 40 A at AC with a C tripping characteristic. The 10 kA breaking capacity per EN 60898 means it safely clears faults up to that level without upstream coordination issues — standard for distribution boards feeding motor control centers or general lighting and socket circuits in industrial panels. The C-curve trips between 5 and 10 times rated current, so it handles moderate inrush from small motors or transformers without nuisance tripping, while still protecting the branch wiring. At 36 mm wide (2 modular units), it snaps onto DIN rail via the quick-assembly system and accepts any mounting position. Pollution degree 3 and overvoltage category III suit it for fixed installations inside enclosures where conductive dust or condensation is expected — typical for mining or heavy industrial environments.
Derating and ambient — what the numbers mean for your panel
The 40 A rating holds at 35 °C ambient. At 40 °C it derates to 37.6 A, at 45 °C to 36.36 A, at 50 °C to 35.04 A, and at 55 °C to 33.68 A. If your panel runs hot — say, packed with contactors and drives — plan the branch load against the derated figure at your actual ambient, not the 40 A headline. The breaker is halogen-free and silicon-free, so no corrosive off-gassing inside the enclosure if it clears a fault. Depth is 76 mm (installation depth 70 mm), height 90 mm. The combined top and bottom terminals accept standard copper conductors, and the sealable cover option lets you lock the breaker position after commissioning — useful for mining or process lines where unauthorized resetting is a safety concern.