What this D-curve 4-pole MCB is for
The Siemens 5SY8610-8 is a SENTRON miniature circuit breaker with a D tripping characteristic, 4 poles (3P+N), rated 10 A at 400 V AC.
Mounting position is any — horizontal, vertical, upside-down, the mechanism works the same. IP20 with conductors connected — fine inside a closed panel, not for wet areas.
Thermal derating — real-world current
The 10 A rating is at 45 °C ambient. At 50 °C it's 9.75 A; at 55 °C it's 9.49 A. The surrounding temperature influence curve goes to 95% RH at 55 °C, 55% at 70 °C, 35% at 75 °C. Halogen-free and silicon-free construction, sealable, with touch protection on the terminals.