What the 5SY4125-7CC carries in the nacelle
The Siemens 5SY4125-7CC SENTRON miniature circuit breaker is a 1-pole, C-curve unit rated 25 A at 400 V AC, with a 10 kA breaking capacity per EN 60898 and 5 kA per UL 1077. That 10 kA IEC number means it will clear a bolted fault up to that level without welding its contacts — critical when you're protecting a pitch-drive supply 100 meters up where an upstream MCCB might be a long coordination step away. C-curve trips between 5 and 10 times rated current, so it handles motor inrush (pitch motors, hydraulic pumps) without nuisance tripping, while still clearing a hard short fast enough to limit let-through energy.
Rated for the shake and the cold
Survives the nacelle: temperature range from -40 °C to 75 °C covers a winter start on a North Sea turbine and a July afternoon in the Sahara. Vibration resistance per IEC 60068-2-6 (±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz) means it won't rattle its internal mechanism loose on a tower that sways a meter at the hub. Pollution degree 3 and overvoltage category III qualify it for the control cabinet in an industrial environment — no special derating for conductive dust or transient overvoltages from switching drives.
Panel fit and wiring
Width is 18 mm (1 width unit), depth 76 mm, height 90 mm. Mounts on a quick-assembly DIN rail — snaps on, no tools. Combined terminals top and bottom accept incoming and outgoing conductors; touch protection is integrated. The 70 mm installation depth leaves room behind a shallow gland plate. Halogen-free and silicon-free construction matters for sensitive atmospheres (offshore, clean room). No neutral conductor switching on this single-pole unit.