SIRIUS 3RV1021-0KA10-0FJ0-ZX95 — motor protection circuit breaker, 1.25 A, 100 kA
The Siemens SIRIUS 3RV1021-0KA10-0FJ0-ZX95 is a motor protection circuit breaker rated for a continuous current of 1.25 A, designed to protect a 0.37 kW motor at 400 V AC. Its 100 kA breaking capacity at 400 V AC means it can safely interrupt a fault current up to that level without cascading upstream — critical for panel coordination studies. The CLASS 10 trip class ensures it disconnects within 10 seconds at 7.2× the thermal setting, matching the startup profile of standard induction motors driving pumps, fans, or conveyors. Snap it onto a 35 mm DIN rail per DIN EN 50022 — the 45 mm width and 97 mm height fit standard motor starter assemblies. Screw-type terminals on the main circuit accept solid or stranded conductors from 1 to 6 mm² (or 14 to 10 AWG), and the IP20 front protection keeps live parts behind the enclosure door. No backwards or side clearance is needed, so it packs tight against adjacent devices.
Ratings that govern the fit
The 100 kA breaking capacity holds across 240 V, 400 V, 500 V, and 690 V AC — that is a flat SCCR curve, not a derated one. For a 1.25 A device this is high headroom; it means the breaker will hold its rating even on a high-fault panel bus. The maximum switching frequency of 15 operations per hour in AC-3 duty limits how often you can cycle a motor start — fine for a conveyor or compressor, not for a rapid-reversing application. Phase failure detection is built in, so the breaker trips on a lost phase before the motor single-phases to failure. Ground fault detection is not included — that would require an external module or a different variant. The auxiliary switch is present (yes), but the base unit carries zero built-in auxiliary contacts; the switch is a separate add-on that mounts to the side. Operating temperature spans -20 to +60 °C, storage and transport from -50 to +80 °C. Shock rated at 25 g for 11 ms, surge voltage withstand at 6 kV. Mount it in any position, up to 2 000 m altitude without derating. The 7.25 W power loss in hot operating state (2.4 W per pole) is the heat you need to vent inside the enclosure.