The Siemens 3RV2021-1BA20 is a SIRIUS motor-protection circuit breaker in the Size S0 frame, designed to protect motor branch circuits against overload and short circuit.
Breaking capacity and what it means for your panel
At 400 V AC this breaker interrupts fault currents up to 100 kA — that is the SCCR (short-circuit current rating) that governs whether the device can clear a bolted fault without rupturing. The same 100 kA holds at 240 V and 500 V AC; at 690 V it still handles 10 kA. That rating is what the panel designer uses to verify the branch circuit withstands the available fault current.
The breaker measures 45 mm wide, 119 mm tall, and 97 mm deep. Mounting position is any orientation. For thermal derating, Siemens calls for 50 mm clearance above and below the device and 30 mm to the side; no clearance needed forward or backward. That matters when you are packing breakers into a shallow enclosure — the 97 mm depth plus wiring space is the dimension that decides gland-plate depth.