The Siemens 3RV1021-4AA38-1KT1 is a SIRIUS motor protection circuit breaker rated for 16 A continuous current, with a Class 10 trip characteristic — meaning it disconnects within 10 seconds at 7.2× the thermal setting, which is the standard for protecting standard induction motors during locked-rotor starts.
Mounting position is any orientation, so it fits in tight corners or vertical bus runs. The 45 mm width means it takes one standard module slot on the rail — no surprises when you're swapping it into an existing panel.
Terminals and wiring
Main circuit uses screw-type terminals accepting 2x (0.25... 2.5 mm²) solid or 2x (24... 14 AWG) stranded. The auxiliary and control circuit uses spring-loaded terminals — so the aux contacts are quicker to land, but the power wires still get the torque-able screw clamp that panel builders prefer for motor circuits.
Auxiliary switch and extras
This variant comes with a factory-fitted transverse auxiliary switch rated 1 A at 24 V, 0.5 A at 230 V, and 0.15 A at 60 V. It also has phase failure detection — so if one phase drops out on a three-phase motor, the breaker trips before the motor cooks on single-phasing. No ground fault detection, so don't expect it to cover leakage-to-earth faults.