The Siemens 5SL6340-7BB is a SENTRON miniature circuit breaker (MCB) — a 3-pole, C-curve device rated 40 A at 30 °C, with a 6 kA breaking capacity per both EN 60898 and IEC 60947-2.
The 40 A rating is at 30 °C ambient; at 40 °C it derates to 37.89 A, at 45 °C to 36.8 A, and at 55 °C to 34.47 A. The 400 V AC rated supply voltage and 440 V AC maximum multi-phase operation cover standard three-phase distribution in most industrial and commercial buildings. The 72 V DC maximum rating means it's not your go-to for DC circuits above that; stick with DC-rated breakers for solar or battery banks.