What it is and what it does
The Siemens SIRIUS 3RV2021-4PA10-ZW96 is a motor protection circuit breaker designed to protect three-phase induction motors against overload and short-circuit. It trips in Class 10, meaning it will disconnect within 10 seconds at 7.2× the thermal setting — fast enough to protect standard IEC motor windings during a stall or locked-rotor event. It carries a 10 kA breaking capacity at 400 V, so it can safely interrupt a fault current up to that level without upstream fuses needing to clear first. That 10 kA rating at 400 V is the number that governs its fit in a panel with a given available fault current — don't size it into a bus with more than 10 kA SCCR at 400 V unless you have current-limiting upstream protection. Phase failure detection is built in — if one line drops, the breaker trips, preventing single-phasing damage to the motor. That's a standard feature on SIRIUS motor-protective breakers, not an add-on module.
Mounting and integration
Mounts via screw and snap-on onto 35 mm standard DIN rail per DIN EN 60715. The 45 mm width means it occupies one standard 45 mm-wide module slot on the rail — plan your panel fill factor accordingly. Depth is 97 mm, which fits most standard enclosures without a deep gland plate. Clearance requirements: 70 mm upwards and downwards, 30 mm at the side, 0 mm forwards and backwards. That 0 mm backwards clearance means it can sit flush against a back panel or busbar support. Terminals are screw-type for the main circuit, accepting 2x (1…2.5 mm²) or 2x (2.5…10 mm²) solid or stranded. Use ferrules on stranded for a reliable connection under vibration.