The Siemens 5SJ6240-7FC is a SENTRON miniature circuit breaker (MCB) — a 2-pole, C-curve device rated 40 A at 400 V AC, with a 6 kA breaking capacity per EN 60898. Rated 72 V DC on each pole, so it handles DC control circuits or small battery-backed loads. The 40 A rating at 30 °C derates to 37.57 A at 40 °C and 36.8 A at 45 °C — expect to downrate by roughly 3 A per 10 °C above 30 °C if the panel runs warm. Pollution degree 2 (typical for clean, non-conductive environments) and overvoltage category III suit it for fixed-installation branch circuits in residential or infrastructure panels.
Lifecycle and sourcing — active, not obsolete
The SENTRON series is Siemens' standard MCB line for residential and infrastructure duty. The 2-pole, 2-module-width (36 mm) format is a common footprint that drops into any standard DIN-rail enclosure. No special adapter or rewiring needed if replacing an equivalent 2-pole C-curve 40 A MCB.
Mounting position any, so vertical or horizontal rail orientation works. Sealable (can be locked in the OFF position with a padlock) — useful for lockout/tagout on a downstream load. Touch protection not fitted as standard; if the panel is open to live busbars, add a finger-safe terminal shield separately.