Motor protection circuit breaker, SIRIUS 3RV2021-1CA20-0BA0
The Siemens 3RV2021-1CA20-0BA0 is a SIRIUS motor protection circuit breaker in size S0, designed for protecting three-phase induction motors against overload, short-circuit, and phase failure. It carries a Class 10 trip class, meaning it will trip within 10 seconds at 7.2× the thermal setting — the standard response for standard-start induction motors driving pumps, fans, and conveyors where the rotor doesn't stall for long. The 100 kA breaking capacity at 400 V AC means this breaker can safely interrupt a fault current up to 100,000 amps at the panel's line voltage without welding contacts or rupturing the enclosure; that's enough for most industrial distribution boards with a transformer upstream. Mounting is screw and snap-on onto 35 mm DIN rail per DIN EN 60715, and the breaker can be installed in any position. The spring-loaded terminals on the main current circuit accept 2x 1 to 10 mm² solid or stranded copper — no torque driver needed for the power connections, which speeds up panel wiring. The 45 mm width and 97 mm depth mean it occupies a single DIN module width and leaves 50 mm clearance above and below for cable bending; zero clearance needed forwards or backwards, so it can be butted against the back panel or a neighboring device.
Breaking capacity and coordination
The 100 kA rated short-circuit breaking capacity at 400 V AC holds across 240 V and 500 V as well. At 690 V it drops to 10 kA — still adequate for 690 V line supplies, but coordination with an upstream fuse or MCCB becomes tighter. The backup fuse recommendation is gG 25 A at 400 V and 500 V, stepping down to gG 20 A at 690 V. That fuse size is the maximum allowed to preserve the breaker's 100 kA rating; a larger fuse would shift the let-through energy above what the breaker can interrupt. Compared to the smaller-frame 3RV2011-0BA20, the 3RV2021-1CA20-0BA0 is the size S0 variant with higher continuous current capacity and the same 100 kA interrupting rating. The 3RV2011-0BA20 is a size S00 breaker with a lower thermal setting range; the 3RV2021-1CA20-0BA0 will not drop into a panel wired for S00 without adjusting the DIN rail mounting clips and terminal spacing. The spring-loaded terminals on this unit are screwless — the S00 sibling often uses screw terminals — so the wiring method differs.
Integration and wiring
The spring-loaded terminals accept solid or stranded conductors 2x 1 to 10 mm². Use a screwdriver with a 3 mm shaft diameter and a 3.0 x 0.5 mm tip to open the clamp — push in, insert the stripped conductor (8-10 mm strip length), release. The breaker's 45 mm width fits a standard DIN-rail enclosure; the 97 mm depth leaves room for wiring behind the panel door. The 50 mm clearance above and below is for cable bending radius; the 30 mm side clearance is for neighboring devices or auxiliary contact blocks. Phase failure detection is built in; ground fault detection is not. For a motor feeder that needs ground-fault protection, add an external ground-fault relay or use a 3RV2 variant with the GF option. The rated operating voltage range is 20 to 690 V, covering 24 V control transformers up to 690 V line supplies. The maximum switching frequency at AC-3 duty is 15 operations per hour — adequate for a motor start once every four minutes, not for jogging or rapid cycling.