The 3RV2021-1BA10-Z W96 is a Siemens SIRIUS 3RV2 motor starter protector in size S0, built for motor branch-circuit protection. Its Class 10 A-release trips between 1.4 A and 2 A, matched to small induction motors in the 0.37–0.75 kW range on 400 V three-phase. The N-release (short-circuit magnetic trip) fires at 26 A, which clears a bolted fault before the contactor welds. That combination — thermal Class 10 plus a magnetic instantaneous at 13× the max FLA — is what keeps this breaker from nuisance-tripping on inrush while still protecting the motor winding during a stall.
Screw terminals accept 0.5–16 mm² conductors, so it lands directly into a 3-pole contactor below without extra bus bars. The multi-unit packaging (24 pieces per pack) tells you this was designed for volume panel builds, not one-off repairs.