What it is and what it does
The Siemens SIRIUS 3RV1021-0GA10-0FJ0-ZX95 is a motor protection circuit breaker — the thing that sits between your contactor and the motor, watching for overload and short-circuit conditions. It's designed for a 0.63 A continuous load, which at 400 V AC-3 duty works out to about 0.18 kW motor protection. The Class 10 trip curve means it will hold through a normal start but trip fast enough to protect the motor windings if the rotor locks. Phase failure detection is built in, so a lost phase won't cook the motor while it single-phases.
Breaking capacity and coordination
The 100 kA breaking capacity at 400 V AC is the headline number here — that's the fault current this breaker can interrupt without welding its contacts or venting plasma. It's rated for 100 kA all the way up to 690 V, which means it can sit downstream of a large transformer without needing a current-limiting fuse upstream for SCCR compliance. The 6 000 V surge voltage rating (impulse withstand) tells you it's built for industrial environments where switching transients are the norm, not the exception.
Mounting and wiring
Snaps onto 35 mm DIN rail per EN 50022, or screws directly to a backplate. At 45 mm wide and 96 mm deep, it's a standard 2-module footprint — no surprises in the panel layout. The screw terminals on the main circuit accept solid or stranded conductors: 2x 1 to 2.5 mm² or 2x 2.5 to 6 mm², with AWG equivalents 14 to 10. That's enough cross-section for the 0.63 A rating plus some margin for voltage drop on longer runs. IP20 on the front face means it's protected against finger contact but not washdown — keep it inside the enclosure.