What this MCB is and what it does
The Siemens 5SY4280-7 is a 2-pole miniature circuit breaker from the SENTRON family, carrying a C-curve trip characteristic. That C-curve means it trips between 5 and 10 times rated current — standard for general-purpose branch circuits feeding motor starters, control transformers, and mixed loads where brief inrush won't nuisance-trip a B-curve breaker. Rated breaking capacity hits 10 kA per IEC 60898-1 at 400 V AC, and 15 kA per IEC 60947-2 at 60 V DC — so it handles fault current on industrial lighting panels, small motor branch circuits, and DC control bus feeds. Also carries a UL 1077 / CSA C22.2 No. 235 supplementary protector rating at 5 kA for North American panels.
Panel fit and mounting
Snaps onto DIN rail via the quick-assembly system — 2 modular width units (36 mm wide). Depth is 76 mm, installation depth 70 mm. Mounts in any position. IP20 with conductors connected, pollution degree 3, overvoltage category III. That means it's rated for inside a standard industrial enclosure, not for wet or outdoor locations. Combined terminals top and bottom accept solid or ferruled stranded copper. Neutral conductor is not switched — it's a 2-pole breaker switching both phases (line and load), not line + neutral. Suitable for mechanical engineering and industry per the suitability listing.
Environmental limits and service life
Operates from -40 °C up to 75 °C ambient. Humidity derating curve: max 95% RH at 55 °C, dropping to 35% at 75 °C. Vibration tested per IEC 60068-2-6: ±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz. Mechanical service life typical 10,000 cycles. Halogen-free and silicon-free construction.