The 5SY6301-8 is a Siemens SENTRON 5SY6 miniature circuit breaker — 3-pole, D-curve, rated 1 A at 400 V AC. The D tripping characteristic means it tolerates the high inrush currents typical of motor loads, transformers, or solenoid valves without nuisance tripping on startup; the magnetic trip threshold sits at 10 to 20 times the rated current, so a 1 A D-curve holds through a 10–20 A surge and clears a hard fault fast.
Any mounting position works, and the IP20 rating (with conductors connected) is standard for enclosed distribution boards; it's not a washdown part.
DC rating and temperature derating
DC rated at 72 V maximum per IEC 60947-2 with 15 kA breaking capacity — useful if the breaker lands in a DC bus or battery circuit, but the 72 V ceiling limits it to nominal 48 V or 60 V systems. Temperature derating follows a stepped curve: full rated current up to 55 °C at 95% humidity, then derate to 55% at 70 °C, and 35% at 75 °C. In a hot panel near a drive or transformer, that derate matters — at 70 °C ambient the breaker effectively handles about 0.55 A continuous, not 1 A.