What it is and what it does
The Siemens 5SY6125-8 is a 1-pole SENTRON miniature circuit breaker (MCB) with a D tripping characteristic, rated 25 A at 400 V AC. It snaps onto a DIN rail via the quick-assembly system and occupies a single 18 mm width unit — standard for panel integration. The D curve means it tolerates high inrush currents — typical for motor, transformer, or lighting ballast loads — without nuisance tripping. For fault clearing, it delivers 6 kA breaking capacity per EN 60898 and 15 kA per IEC 60947-2, so it handles moderate fault levels in industrial sub-distribution. Rated for 400 V AC (overvoltage category III) and up to 72 V DC, with a maximum 15 kA DC breaking capacity per IEC 60947-2. The housing is halogen-free and silicon-free, and touch protection is built in.
Where it fits
Mounts in any position on a DIN rail; installation depth is 70 mm, overall depth 76 mm. The combined terminals at top and bottom accept wiring from any direction, and the breaker is sealable for panel-lockout procedures. IP20 with connected conductors — suitable for enclosed panel use, not for washdown or outdoor exposure. Ambient range spans -40 °C to 75 °C, with derating for humidity above 55 °C.