Siemens 5SY4280-6 — 2-pole B-curve MCB for general distribution
The Siemens 5SY4280-6 is a 2-pole miniature circuit breaker from the SENTRON series, rated 80 A at 35 °C with a B tripping characteristic. It breaks fault currents up to 10 kA per EN 60898 at 400 V AC, 50/60 Hz — enough for most commercial and light industrial sub-distribution boards. The B-curve trips between 3 and 5 times rated current, so it handles resistive and small motor loads without nuisance tripping from inrush.
Thermal derating and ambient limits
Rated current drops with panel ambient temperature: 80 A at 35 °C, 74.16 A at 45 °C, 72.16 A at 50 °C, 70 A at 55 °C, and 67.84 A at 60 °C. If the enclosure runs hot — say next to a transformer or in a sealed cabinet — size the upstream protective device for the derated figure, not the 35 °C nameplate. The MCB itself is rated for ambient from -40 °C to 75 °C, and humidity limits are specified per.
Mounting and integration
Snaps onto DIN rail via the quick assembly system; mounting position is any. Width is 36 mm (2 modular units), depth 76 mm, installation depth 70 mm. Combined terminals top and bottom accept conductors; touch protection is built in. Pollution degree 3 and overvoltage category III suit fixed-installation panels. IP20 with connected conductors — no washdown rating, so keep it inside the enclosure.