Siemens 5SY8310-8 SENTRON MCB — D Curve, 3-Pole, 40 kA
The Siemens 5SY8310-8 is a SENTRON miniature circuit breaker (MCB) with a D tripping characteristic, 3 poles, and a rated breaking capacity of 40 kA at 400 V AC per IEC 60947-2. At 60 V DC it interrupts 15 kA per the same standard, and under UL 1077 it is rated for 5 kA.
That is a high-interrupting rating for a 3-MW-wide device — it belongs in a panel with a substantial upstream transformer or a high-fault utility feed. The 15 kA DC rating at 60 V covers battery-backed or rectified DC bus circuits common in industrial control. That is deliberately high: it passes the starting surge of a motor, a power supply capacitive bank, or a welding transformer without opening. The trade-off is that a hard short circuit on a long cable run may not be seen as quickly as with a B or C curve — coordination with downstream protection matters. Ambient derating is specified: max 95% humidity at 55 °C, 55% at 70 °C, and 35% at 75 °C. In a non-climate-controlled enclosure (rooftop, desert, freezer aisle), you stay within that envelope. The vibration resistance per IEC 60068-2-6 (±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz) covers typical industrial machinery vibration.
The 5SY8310-8 is certified to IEC / EN 60947-2 and UL 1077. It is halogen-free and silicon-free — relevant for panels in semiconductor fabs, medical device manufacturing, or any cleanroom where outgassing contaminants must be avoided. That is not a wear-out limit for most panel applications — it is a reliability benchmark for the mechanism.