What it is and where it lands
The Siemens SIRIUS 3RV2021-1KA10-0DA0 is a circuit breaker designed for system protection — meaning it sits upstream of a motor starter or contactor to guard against short circuits and overloads in the distribution path, not as a standalone motor-protective device. It's part of the SIRIUS family, S0 frame size, which is the compact footprint for motor feeders up to around 7.5 kW at 400 V. Mounting is screw and snap-on onto 35 mm DIN rail per DIN EN 60715, so it integrates into any standard panel without adapters.
Breaking capacity — the number that decides selectivity
At 400 V AC, this breaker interrupts 100 kA. Same at 240 V AC. At 500 V AC it's 42 kA, and at 690 V AC it drops to 6 kA. That 100 kA at 400 V is the headline — it means this part can sit on a high-fault panel bus without needing upstream current-limiting fuses for most industrial distributions. The 6 kA at 690 V is still adequate for a 690 V motor feeder where the transformer impedance limits fault current, but you'd check coordination if the bus SCCR exceeds that.
Motor protection and trip class
Rated motor power at 230 V is 3 kW. Trip class is CLASS 10 — that's the standard for standard-duty motor starts (pumps, fans, compressors) where the start time stays under 10 seconds. If you're driving a high-inertia load like a centrifuge or a large flywheel, CLASS 10 may trip on start; you'd step to CLASS 20 or 30. The breaker accepts 2x (1 to 2.5 mm²) or 2x (2.5 to 10 mm²) solid or stranded wire at the main contacts, M4 screw terminals.
Environmental and mounting
Operating temperature range is -20 to +60 °C; storage and transport range is -50 to +80 °C. Mounting position is any. Clearances: 50 mm upwards, 50 mm downwards, 30 mm at the side, 0 mm forwards and backwards — so it can be stacked tight front-to-back in a shallow enclosure. Dimensions: 45 mm wide, 97 mm high, 97 mm deep. The S0 frame is the same width as the S00 but taller, so if you're swapping from an S00 breaker, check the height clearance in your enclosure.