The Siemens 5SY5440-7 is a SENTRON 4-pole miniature circuit breaker rated 40 A at AC with a C tripping characteristic and a 10 kA breaking capacity per EN 60898. The 4-pole design (4P) switches all three phases plus the neutral, which is what you want for a three-phase motor feeder where you need to isolate the neutral for maintenance. The 4 MW width (72 mm) takes up four 18 mm modular slots on the DIN rail — standard for a 4-pole MCB in this class.
Temperature derating — the real-world current
The 40 A rating holds at 35 °C ambient. At 40 °C it derates to 38.4 A; at 50 °C it's 36.76 A; at 60 °C it's 35.04 A. The humidity limits are 95% RH up to 55 °C, then dropping to 35% RH at 75 °C, so a sealed outdoor enclosure that traps moisture could be a problem.
The quick-assembly system means you can gang multiple breakers on a busbar without extra hardware.