What it is and what it does
The Siemens 3RV2021-4EA25 is a SIRIUS motor protection circuit breaker designed for protecting three-phase motors against overload, short-circuit, and phase failure. It snaps onto a 35 mm DIN rail per DIN EN 60715 and uses spring-loaded terminals for the main current circuit, saving panel wiring time.
Key ratings and what they mean for your panel
Rated breaking capacity of 25 kA at 400 V means this breaker can safely interrupt fault currents up to that level without upstream fuses needing to clear first — critical for SCCR compliance on a motor branch circuit. Trip Class 10 means the bimetal releases within 10 seconds at 7.2× the thermal setting, matching the typical locked-rotor withstand of standard induction motors. Phase failure detection is built in, so a lost leg trips the breaker rather than letting the motor single-phase. The 45 mm width (3 module spaces) and 97 mm depth fit standard 600 mm deep enclosures. Mounting position is any, so vertical or horizontal DIN rail orientation works. Clearance: 50 mm above and below, 30 mm at the sides for arc venting and heat dissipation.