What it is and what the ratings mean
The Siemens 5SY4205-8 is a 2-pole miniature circuit breaker from the SENTRON family, built to IEC/EN 60898-1 and IEC 60947-2 / UL1077. The D tripping characteristic means it tolerates high inrush currents — think motor starts, transformer energization, or welding equipment — without nuisance tripping on the magnetic element. Rated 400 V AC with a breaking capacity of 10 kA per EN 60898-1 and 35 kA per IEC 60947-2; DC rating is 15 kA per IEC 60947-2. That 35 kA figure is the one that matters for industrial panel coordination — it tells you this breaker handles a serious fault current without venting.
Mounting and integration notes
Fastens via the quick assembly system — no tools needed to clip onto the DIN rail. Installation depth is 70 mm; overall depth with terminals is 76 mm. Accepts combined terminals top and bottom, so you can bus-bar the line side without extra adapters. Pollution degree 3 and overvoltage category III suit it for fixed-installation industrial panels. IP20 with connected conductors — keep the panel door closed if you expect washdown. Vibration rated per IEC 60068-2-6: ±1 mm at 5 to 25 Hz, 50 m/s² at 25 to 150 Hz. Mechanical life is 10 000 operating cycles typical.