Motor protection circuit breaker with overload relay — SIRIUS 3RV2121-4CA10
It combines the two functions into one compact unit, saving panel space and wiring compared to a separate circuit breaker plus thermal overload relay. This is the correct class for general-purpose motor starting; a Class 20 would allow longer acceleration but provides less protection against sustained overload.
Short-circuit ratings and selectivity planning
This breaker carries a short-circuit breaking capacity of 25 kA at 400 V AC, 100 kA at 240 V, 5 kA at 500 V, and 2 kA at 690 V. For most 400 V industrial distribution panels, the 25 kA SCCR provides adequate headroom; if the available fault current exceeds that, you would need to coordinate with an upstream current-limiting fuse or MCCB rated higher. The listed fault-current ratings are for gL/gG fuses in series — at 400 V the maximum fuse rating is 63 A, and at 500 V and 690 V it is 50 A. This coordination data allows the panel designer to select the upstream fuse such that the breaker remains the protective device for downstream motor faults without unwanted fuse blowing.
The 65 mm width occupies three standard 18 mm DIN-rail module slots, leaving room for auxiliary contact blocks or a separate contactor alongside. Screw-type terminals on the main circuit accept 2 × (0.5…1.5 mm²) or 2 × (0.75…2.5 mm²) solid or stranded wire. The main contact screws are M4.