The Siemens 5SY4108-8CC is a 1-pole miniature circuit breaker from the SENTRON 5SY series, sized at 1 modular width unit (18 mm) for DIN-rail mounting in distribution boards and control panels. Its D tripping characteristic means it tolerates the high inrush currents of motor and transformer loads — the magnetic trip threshold sits between 10× and 20× rated current, so it won't nuisance-trip on a motor start but clears hard faults fast. Rated 8 A at 40 °C ambient, the breaker delivers 10 kA breaking capacity per EN 60898 (5 kA per UL 1077 / CSA C22.2 No.235), which covers most industrial and commercial panel fault levels. The 1-pole design switches the line conductor only — no neutral pole — so it's intended for single-phase branch circuits or as a phase leg in multi-pole assemblies.
Temperature derating — the real current rating
The 8 A rating holds only up to 35 °C. Above that, the breaker must be derated: 7.35 A at 40 °C, 7 A at 45 °C, 6.63 A at 50 °C, and 6.25 A at 55 °C. If your panel runs warm — say 50 °C inside the enclosure — the usable continuous current drops to 6.63 A. Plan the branch circuit load against the derated value at your actual ambient, not the 35 °C sticker figure.
IP20 with connected conductors — standard for panel-internal use.