The Siemens 5SL7150-8RC is a 1-pole miniature circuit breaker rated 240/415 V with a 10 kA breaking capacity and a D tripping characteristic at 50 A. This is the part you spec when the load has a starting surge that would trip a B or C curve breaker.
The 1-pole form factor takes up a single module width, so it fits into a crowded sub-distribution board without eating into spare ways. For a panel OEM wireman, the wiring is straightforward — line in at the top, load out at the bottom, and the D curve handles the motor-start transient on a compressor or conveyor drive.