What this breaker does in the panel
The Siemens 3RV2021-1EA25 is a SIRIUS motor protection circuit breaker designed to protect motor branch circuits against overload and short circuit. It carries a CLASS 10 trip characteristic, meaning it will trip within 10 seconds at 7.2× the thermal setting — appropriate for standard induction motor starts where the inrush decays quickly. Phase failure detection is built in, so a lost phase on the line side will cause the breaker to open before the motor single-phases to failure. The interrupting ratings are substantial: 100 kA at 240 V, 400 V, and 500 V, dropping to 4 kA at 690 V. That SCCR headroom means this breaker can be used in high-fault panels without requiring upstream current-limiting fuses, as long as the available fault current stays under those thresholds. The 4 A rating at 480 V and 600 V tells you this is a low-current frame — sized for fractional-horsepower motors up to about 0.75 hp at 230 V.
Mounting and wiring — DIN rail fit
Mounts via screw and snap-on onto 35 mm DIN rail per DIN EN 60715. The 45 mm width and 97 mm depth mean it occupies a single modular slot on the rail, leaving room alongside contactors and auxiliary blocks. Spring-loaded terminals on the main current circuit accept 2× (0.5 to 2.5 mm²) solid or stranded conductors — no screw torque to verify, just strip and push. Any mounting position is allowed, so vertical or horizontal rail orientation is fine.