What it is and what it does
The Siemens 3RV2021-1FA10 is a SIRIUS motor protection circuit breaker designed for motor protection. It combines a circuit breaker and overload relay in one unit, sized for a 45 mm wide DIN-rail footprint (screw and snap-on mounting onto 35 mm DIN rail per DIN EN 60715). Trip Class 10 means it trips within 10 seconds at 7.2× the thermal setting — standard for protecting standard induction motors during startup without nuisance tripping on normal acceleration. Rated breaking capacity hits 100 kA at 240 V AC, 400 V AC, and 500 V AC — that's the fault current it can safely interrupt without welding contacts or cascading upstream. At 690 V AC it still manages 4 kA. Phase failure detection is built in, so a lost phase on the line side will trip the breaker before the motor single-phases and burns out.
Panel fit and mounting
At 45 mm wide and 97 mm deep, this breaker occupies a single 45 mm slot on the DIN rail. Mounting position is any — vertical, horizontal, or upside-down — so it fits tight enclosures without derating the trip curve. Clearance requirements: 50 mm above and below for cooling and arc chute venting, 30 mm to the side. No space needed forward or backward. Main circuit terminals accept 2× (1 to 2.5 mm²) or 2× (2.5 to 10 mm²) solid or stranded copper, M4 screw terminals.