The Siemens SIRIUS 3RV2021-1KA10-ZX95 is a motor protection circuit breaker in size S0, designed to protect three-phase motors against overload and short-circuit faults. It carries a CLASS 10 trip class, meaning it will trip within 10 seconds at 7.2× the set current — fast enough to protect standard induction motors from overheating during a locked-rotor condition. The adjustable overload release (A-release) covers 9 to 12 A, and the magnetic short-circuit release (N-release) is fixed at 163 A.
Breaking capacity and selectivity
At 400 V AC, this breaker interrupts up to 100 kA — that is the full prospective short-circuit current it can safely clear without welding its contacts or rupturing. At 500 V AC it still handles 42 kA, and at 690 V AC it manages 6 kA. These figures let you coordinate downstream contactors and feeders: the breaker takes the high fault energy, so the contactor only needs to break its own rated current. For a 12.5 A motor circuit on a 400 V supply with a high available fault current (say, near a large transformer), this breaker gives you the SCCR headroom to avoid cascading failures upstream.
Panel integration and wiring
The breaker snaps onto a 35 mm DIN rail per DIN EN 60715 and accepts screw terminals for the main circuit. The A-release is set via a rotary dial on the front; the handle shows the switching status visually. An integrated auxiliary switch (1 NO + 1 NC contact) is included, so you can feed a PLC input or a contactor coil without adding a separate block. The size S0 footprint — 45 mm wide — matches the standard SIRIUS contactor comb footprint for direct motor starter assemblies.