What this SIRIUS motor protection breaker delivers
The Siemens SIRIUS 3RV2021-4AA15-ZX95 is a motor protection circuit breaker designed for the 20 to 690 V range, with a Trip Class 10 characteristic that matches standard IEC motor starting profiles — it lets the motor draw locked-rotor current for up to 10 seconds before tripping, which covers most direct-on-line starts without nuisance trips. Rated breaking capacity hits 25 kA at 400 V, so it can interrupt a bolted fault at the motor terminals without relying on an upstream fuse for that level. For higher prospective fault currents, the spec calls for back-up fuses: gL/gG 63 A at 400 V, 50 A at 500 V, 40 A at 690 V. No ground fault detection on this variant, so plan for a separate ground-fault relay if the application requires it.
The 45 mm width (three module spaces) and 97 mm depth mean it fits a standard distribution board or motor control center bucket without crowding adjacent devices. Clearance requirements: 50 mm upwards and downwards, 30 mm at the side, 0 mm forwards and backwards. That side clearance is tighter than some competitors — check that the adjacent breaker or contactor doesn't overhang into the 30 mm zone. Main contact terminals accept M4 screws, with wire capacity up to 2x 2.5 mm² stranded or solid.
Operating conditions and ratings
Rated operational voltage covers 20 to 690 V AC. Maximum switching rate under AC-3 duty is 15 operations per hour. 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 integrated auxiliary contacts — useful for feeding a PLC input or a status lamp.