What it is and where it fits
The Siemens 3RV2021-1KA25 is a SIRIUS motor protection circuit breaker designed for motor protection. It mounts via screw and snap-on onto a 35 mm standard mounting rail per DIN EN 60715, making it a direct drop-in for any IEC panel with that rail profile. Trip Class CLASS 10 means it will trip within 10 seconds at 7.2× the thermal setting — fast enough to protect standard induction motors from locked-rotor heating without nuisance tripping on normal starting inrush. Rated voltage spans 20 to 690 V AC, covering most low-voltage motor feeds in industrial plants. The interrupting capacity hits 100 kA at both 240 V and 400 V, giving solid SCCR headroom for high-fault panels.
Integration and mounting
Width is 45 mm, depth 97 mm, height 119 mm. The compact 45 mm width fits standard 45 mm-spaced DIN-rail slots, leaving room for adjacent contactors or overloads in a motor starter assembly. Spring-loaded terminals on the main current circuit accept 2× (0.5 to 2.5 mm²) solid or stranded wire — no screwdriver needed for termination, which speeds panel wiring and reduces torque errors. Mounting position is any, so vertical, horizontal, or upside-down orientation in the enclosure is fine. Clearance requirements: 50 mm upward, 50 mm downward, 30 mm to the side.
Lifecycle and sourcing
Phase failure detection is built in, which is critical for three-phase motor protection — if a phase drops, the breaker trips before single-phasing damages the winding.