What this breaker does in a panel
The Siemens 5SY8150-8 is a 1-pole SENTRON miniature circuit breaker with a D tripping characteristic, rated 50 A at 440 V AC multi-phase. The D curve means it tolerates high inrush currents — think motor starting, transformer energization, or welding equipment — without nuisance tripping. It breaks up to 20 kA under IEC 60947-2 at 440 V AC, and 15 kA at 72 V DC, so it handles substantial fault energy on industrial distribution. The 18 mm width (one modular unit) snaps onto DIN rail and leaves room for other gear in the enclosure.
Sizing and derating for real panels
At 45 °C the breaker holds its full 50 A rating. At 50 °C it derates to 48.75 A; at 55 °C, 47.45 A. That's a shallow derating curve — you don't lose much headroom in a warm cabinet. The 76 mm depth plus 70 mm installation depth means it fits standard distribution boards without sticking past the gland plate. Mount it in any position; the quick-assembly system clips onto the rail without tools. Terminal design is combined top and bottom, with touch protection built in.
Environmental and compliance fit
Rated for pollution degree 3 and overvoltage category III — typical for industrial panels, not just residential. Halogen-free and silicon-free construction, sealable, and rated from -40 °C to 75 °C ambient. IP20 with connected conductors. The 5SY8150-8 is designed for mechanical engineering and industry applications per Siemens suitability designation.