The Siemens 5SY6520-8CC is a SENTRON miniature circuit breaker (MCB) with a D tripping characteristic, rated 20 A at AC, and a breaking capacity of 6 kA per EN 60898. It's a 2-pole unit wired as 1P+N — the neutral pole switches with the line, which matters when you need isolation on both sides of the load without a separate disconnect. The D-curve means it tolerates high inrush currents (5-10x rated), so it's the right pick for motor starters, transformers, or welding equipment where a B or C curve would nuisance-trip on startup.
Sizing and derating
Full rating holds at 35 °C ambient. At 40 °C it derates to 18.8 A, at 50 °C to 17.52 A, and at 55 °C to 16.84 A. If the panel runs hot — say inside a non-ventilated enclosure near a drive — size the branch circuit for the derated value, not the 20 A nameplate. The breaker is 36 mm wide (2 modular units), 76 mm deep, and mounts in any position on a DIN rail via the quick-assembly system. Installation depth is 70 mm, so it fits standard 80 mm deep enclosures without the gland plate hitting the back.
Environmental and compliance
Halogen-free and silicon-free construction — relevant for clean-room or semiconductor-adjacent panels where outgassing contaminates optics or contacts. Sealable per the spec, so a panel builder can lock the toggle position with a seal wire. Pollution degree 3, overvoltage category III, IP20 with conductors connected. Vibration resistance per IEC 60068-2-6: ±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz. Operating temperature range -40 °C to 75 °C, with humidity limits derated above 55 °C.