What it is and what it does
The Siemens SENTRON 5SY6240-7CC is a 2-pole miniature circuit breaker (MCB) with a C tripping characteristic, rated 40 A at 35 °C ambient and 6 kA breaking capacity per EN 60898. It's designed for AC circuits at 50/60 Hz, overvoltage category III, pollution degree 3 — standard for industrial control panels and distribution boards. The C-curve means it trips between 5 and 10 times rated current, so it handles motor inrush and transformer energization without nuisance trips on a lighting or general-purpose load.
What the ratings mean for fit
At 36 mm wide (2 modular width units) and 76 mm deep (70 mm installation depth), it snaps onto a standard DIN rail via the quick assembly system and can be mounted in any position. The combined terminal top and bottom accepts conductors for panel wiring. IP20 with connected conductors means it's protected against finger contact once wired — fine inside a closed enclosure, not for wet locations. The 40 A rating derates with ambient temperature: 37.6 A at 40 °C, 36.36 A at 45 °C, 35.04 A at 50 °C, 33.68 A at 55 °C. If your panel runs hot, size the upstream protection for the derated value, not the 35 °C number. Energy limitation class 3 means it limits let-through energy well — good for downstream equipment protection. Halogen-free and silicon-free construction matters for environments where outgassing can contaminate optics or contacts — semiconductor fabs, medical device assembly, or clean-room adjacent panels. Sealable design allows the installer to lock the toggle position with a padlock for lockout/tagout.