Motor protection circuit breaker, SIRIUS series — 3RV2021-0KA25
The Siemens 3RV2021-0KA25 is a SIRIUS-series motor protection circuit breaker designed for motor protection duty. It carries a 100 kA interrupting rating at 400 V, which means it can safely clear a bolted fault on a motor branch circuit without upstream fuse or breaker coordination concerns — a solid choice for MCC buckets or individual motor starters where high available fault current is present. Trip Class 10 means the overload element opens within 10 seconds at 7.2× the thermal setting, matching standard IEC motor starting profiles for pumps, fans, and light conveyors. Phase failure detection is built in, so a single-phased motor will trip before winding damage sets in. The main current circuit uses spring-loaded terminals, accepting 2x (0.5... 2.5 mm²) solid or stranded copper — no screw torque check needed on the power connections. Mounting is screw-and-snap onto 35 mm DIN rail per DIN EN 60715; the 45 mm width matches the standard SIRIUS compact footprint, leaving room for auxiliary contact blocks or a separate contactor alongside.
Panel fit & environment
The 45 mm width and 97 mm depth let it drop into a standard 35 mm DIN-rail enclosure with room for a 3-pole contactor on the same rail. Operating temperature range is -20 to +60 °C, storage -50 to +80 °C — fine for most indoor industrial panels; no special derating needed for ambient up to 60 °C.