The Siemens SIRIUS 3RV2021-1EA20-0BA0 is a motor protection circuit breaker in the S0 frame size, designed to protect three-phase motors against overload, short-circuit, and phase failure. It is rated 4 A at AC-3 duty at 400 V, with a Trip Class 10 characteristic — meaning it will trip within 10 seconds at 7.2× the thermal setting, fast enough to protect standard induction motors during a locked-rotor start. The breaker's 100 kA breaking capacity at 400 V AC allows it to safely clear a bolted fault on a high-capacity distribution bus without upstream coordination issues.
DIN-rail fit and wiring
Mounts via screw and snap-on onto 35 mm DIN rail per DIN EN 60715, in any position. The S0 footprint is 45 mm wide by 119 mm tall, with a depth of 97 mm — a tight fit for a 4-pole device in a crowded enclosure. Main circuit connections use spring-loaded terminals accepting 2× (1 to 10 mm²) solid or stranded wire, which speeds panel wiring and eliminates the need for torque checks on power terminations. Clearance requirements: 50 mm above and below, 30 mm to the sides, zero forward or backward.
Breaking capacity and duty ratings
Breaking capacity holds at 100 kA up to 500 V AC, dropping to 6 kA at 690 V AC. That 100 kA figure at 400 V means the breaker can be used on a transformer-fed panel with a high prospective fault current — no need for a current-limiting upstream fuse for SCCR compliance. The AC-3 rating of 4 A at 400 V corresponds to switching a motor load of approximately 0.8 kW at 230 V. The breaker also carries a maximum operating voltage of 690 V AC-3. Power dissipation in hot operating state is 7.25 W per pole at rated current — factor that into enclosure thermal calculations.