The Siemens 5SY7640-8 is a 4-pole (3P+N) SENTRON miniature circuit breaker with a D tripping characteristic, rated 40 A at 35 °C and 400 V AC. That D-curve means it's built for loads with high inrush — motor starters, transformers, discharge lighting — where the magnetic trip holds off until 10–20× rated current, then clears fast.
The 40 A rating holds at 35 °C ambient. Above that, the thermal element derates: 38.08 A at 40 °C, 37.08 A at 45 °C, 36.08 A at 50 °C, 35 A at 55 °C, and 33.92 A at 60 °C. If the panel runs hot — say 50 °C inside a sealed enclosure — the breaker's effective continuous current drops to 36.08 A. The operating range spans -40 °C to 75 °C, with humidity limits of 95% up to 55 °C, 55% up to 70 °C, and 35% up to 75 °C.
Integration notes
Position of the supply cord is any, which simplifies panel layout when the feed comes from an unexpected side. The sealable feature (tamper-evident cover over the toggle) is useful for installations requiring lockout-tagout or anti-tamper compliance. Touch protection is built into the terminal design.