The Siemens SIRIUS 3RV2021-4CA10-ZX95 is a motor protection circuit breaker designed for screw and snap-on mounting onto 35 mm DIN rail per DIN EN 60715. It carries Trip Class 10, meaning it will trip within 10 seconds at 7.2x the thermal setting — standard for protecting standard induction motors during startup without nuisance tripping on normal inrush.
Breaking capacity and ratings
This breaker delivers a 100 kA interrupting rating at 240 V, dropping to 25 kA at 400 V, and 2 kA at 690 V. That 100 kA at 240 V is the number that matters for high-fault panels common in North American 240 V delta systems — it can clear a bolted fault upstream of the motor starter without needing a current-limiting fuse ahead of it. At 480 V it is rated 22 A, at 600 V also 22 A, so for a 480 V motor branch the continuous current limit is 22 A.
Mounting and integration
The 45 mm wide body fits a standard DIN-rail footprint — three of these side by side occupy 135 mm, leaving clearance for adjacent devices. Requires 50 mm clearance above and below, 30 mm at the sides, and zero forward/backward clearance. Screw terminals for the main circuit accept 2x (1 to 2.5 mm²) or 2x (2.5 to 10 mm²) solid or stranded copper. Phase failure detection is built in, so a lost phase on the line side will trip the breaker — no separate phase-loss relay needed.