The Siemens SIRIUS 3RV2021-4AA40 is a motor protection circuit breaker designed for the 20 to 690 V range, with a Trip Class 10 characteristic that clears overloads before the motor winding reaches critical temperature. Its 25 kA breaking capacity at 400 V means it can safely interrupt a bolted fault up to that level without upstream fuses needing to clear first — sized for a typical 480 V panel with an available fault current of 18 kA, you have headroom. Phase failure detection is built in, so a lost line on a three-phase motor won't let the remaining phases cook the winding. No ground-fault detection on this variant — that's a separate module if you need it.
Mounting and integration
Snaps onto 35 mm DIN rail per DIN EN 60715 and can be screw-mounted as well. Any mounting position is allowed. The 45 mm width fits a standard 45 mm slot on a DIN rail assembly; depth is 97 mm, so plan for 100 mm clearance behind the gland plate. Ring cable lug connection on the main circuit — M4 terminal screws. Clearance requirements: 50 mm above and below, 30 mm to the side, zero forward or backward. That's tight enough for a dense panel if you stagger the breakers.
Breaking capacity by voltage
The interrupting ratings step down with voltage: 100 kA at 240 V AC, 25 kA at 400 V, 5 kA at 500 V, 2 kA at 690 V. The gL/gG fuse coordination limits are 63 A at 400 V, 50 A at 500 V, and 40 A at 690 V — upstream fuse sizing must stay within those limits to guarantee the listed breaking capacity.
Ambient conditions
Rated for operation from -20 to +60 °C, with temperature compensation active across that range. Storage and transport handle -50 to +80 °C. Maximum switching rate under AC-3 duty is 15 operations per hour.