The Siemens 3RV2021-0GA15 is a SIRIUS series motor protection circuit breaker — the device that sits between your contactor and the motor, watching for overload and short-circuit conditions. It's designed specifically for motor protection, not general branch circuit protection, which means the trip curve is shaped to let a motor's inrush pass while still catching a locked-rotor event fast enough to keep the winding from cooking. If you're protecting a high-inertia load that needs a longer acceleration ramp, you'd want Class 20 or 30; this one is sized for the common case. In a panel fed by a transformer of several hundred kVA, that 100 kA rating gives you headroom for high-fault installations without needing a current-limiting upstream breaker.
Mounting position is any orientation, so you're not forced into a specific layout.
No ground fault detection on this variant. Rated insulation voltage is 20 to 690 V, covering standard low-voltage systems up to 690 V phase-to-phase. The auxiliary contact ratings: 1 A at 24 V, 0.5 A at 120/125/230 V, 0.15 A at 60 V — these are the switching capacities for the signal contact, not the main power path.