What it is and what it does
The Siemens 3RV2021-1KA10 is a SIRIUS motor protection circuit breaker designed specifically for motor protection. It combines a contactor and overload relay in one device, with a Class 10 trip characteristic that matches the thermal curve of standard three-phase induction motors — meaning it will ride through a normal start-up but trip fast enough on a locked rotor to protect the winding. Phase failure detection is built in, so a lost phase on the line side won't cook the motor while the breaker holds current on the remaining two legs. Ground fault detection is not included, so if that's required you'll need an add-on module or a separate ground-fault relay.
Breaking capacity and coordination
This breaker is rated for 100 kA at 240 V AC and 400 V AC, 42 kA at 500 V, and 4 kA at 690 V. Those numbers tell you the maximum fault current it can safely interrupt at each voltage level — critical for SCCR (short-circuit current rating) compliance in a panel. At 480 V the rated operational current is 12.5 A, and the same at 600 V, so it's sized for smaller motor branches (typically up to about 10 hp at 575/600 V).
Mounting and wiring
Mounts on 35 mm DIN rail per DIN EN 60715, using either the snap-on latch or screws. The 45 mm width (three module spaces) fits standard distribution boards. Wiring is via screw terminals on the main circuit; accepts solid or stranded copper up to 2x 10 mm² per terminal, with M4 screws. Any mounting position is allowed, so you can lay it sideways in a tight gland plate if needed.
Environmental and lifecycle
Rated for operation from -20 to +60 °C, storage and transport from -50 to +80 °C. The lifecycle stage is marked as current production, so this is a standard catalog item — no end-of-life notice, no last-time-buy pressure. It's a fast mover in the SIRIUS line, and we source it to order against an RFQ.