It's designed to protect motor loads, not general distribution circuits, so it carries phase-failure detection and a Class 10 trip curve, meaning it will clear a stalled-rotor condition fast enough to keep the windings from cooking. Out here in the grease, that's the difference between swapping a breaker and rewinding a motor.
That matters when you're shoehorning this into an existing panel — you need breathing room for the arc chute to do its job. Terminals are screw-type for the main current circuit, accepting 2x 1–2.5 mm² or 2x 2.5–10 mm² solid or stranded. Main contact screws are M4.
If you're cross-referencing from a different manufacturer's motor-protection breaker, the key fit parameters are the 45 mm width, the Class 10 trip characteristic, and the 100 kA SCCR at your system voltage — those are the numbers that decide whether it drops in without a panel re-spin.
If you're protecting a submersible pump or a conveyor motor that starts under load, Class 10 is the right call; Class 20 would let the motor sit at locked-rotor current longer, and that's how you cook the insulation. Phase-failure detection is built in — if one leg drops out, the breaker trips. That's important on a three-phase motor because single-phasing will draw high current in the remaining phases and burn the winding fast. Some economy breakers skip this; the 3RV2021-1EA10 does not. Rated operating voltage spans 20 to 690 V — covers everything from 24 V control transformers up to 690 V industrial mains.