The Siemens SIRIUS 3RV2021-1KA20 is a motor protection circuit breaker designed for the main current circuit of induction motors. It provides overload and short-circuit protection up to 100 kA at 400 V AC, with Trip Class 10 release characteristics — meaning it trips within 10 seconds at 7.2× the thermal setting, matching the startup profile of standard squirrel-cage motors. Phase failure detection is built in, so a lost phase on the line side will trip the breaker before single-phasing damages the motor winding. Ground fault detection is not included — if that's required, pair this with a separate ground-fault relay or specify the 3RV2021-4CA25 variant that includes it. Spring-loaded terminals accept 2× (1 to 10 mm²) solid or stranded conductors, which covers most motor feeder sizes up to the 12.5 A continuous rating at 480/600 V. The 45 mm width and 97 mm depth fit standard 35 mm DIN rail per DIN EN 60715, with screw and snap-on mounting in any position.
Breaking capacity and motor sizing
The 3RV2021-1KA20 delivers 100 kA at 240 V AC and 400 V AC, 42 kA at 500 V AC, and 4 kA at 690 V AC. That 100 kA at 400 V is the headline number — it means this breaker can safely interrupt a fault current up to 100,000 A on a 400 V line without welding contacts or rupturing the case, which covers most industrial distribution panels with transformer ratings up to 2.5 MVA. Motor horsepower equivalents: 2 hp at 230 V, 3 hp at 220/230 V, 8 hp at 460/480 V, 10 hp at 575/600 V. The 12.5 A continuous rating at 480 V and 600 V aligns with NEMA size 1 motor starters for those horsepower ranges.
Lifecycle and sourcing
For a critical spare holding on a legacy panel, this is the one to keep in the cabinet. The Class 10 trip curve and 45 mm width are fixed — if the panel was wired for the 3RV2021-4CA25 (which adds ground-fault detection), the 3RV2021-1KA20 will drop into the same DIN rail slot and terminal footprint, but you lose the ground-fault function.
Environmental and mounting
Operating temperature range is -20 to +60 °C; storage and transport range is -50 to +80 °C. The 50 mm upwards and downwards clearance and 30 mm side clearance are required for arc flash venting and heat dissipation — no forward or backward clearance needed. Mount in any position on 35 mm DIN rail per DIN EN 60715. The screw and snap-on fastening method lets you screw it down for vibration resistance or snap it on for quick replacement — useful when the panel is in a high-vibration area like a conveyor line or compressor skid.