What it is and where it fits
The Siemens 3RV2721-4CD10 is a SIRIUS circuit breaker in the S0 frame size, designed for system protection per UL 489 and CSA C22.2 No. 5. It mounts via screw and snap-on onto 35 mm DIN rail per DIN EN 60715, in any mounting position. Rated voltage range spans 20 to 690 V, with a 25 kA breaking capacity at 400 V AC and 55 kA at 400 V AC under the UL/CSA rating path. At 230 V, it handles motor loads up to 5.5 kW.
Breaking capacity and selectivity
The 25 kA SCCR at 400 V AC means this breaker can safely interrupt fault currents up to that level without cascading upstream — critical for panel coordination in industrial distribution. At 690 V AC, the breaking capacity drops to 2 kA (IEC) or 4 kA (UL), so verify the available fault current at your service voltage. Backup fuse ratings are specified per voltage: gG 63 A at 400 V, gG 50 A at 500 V and 690 V. These limit let-through energy and protect downstream components during a high-fault event.
Panel integration and clearances
Dimensions: 45 mm wide, 97 mm deep, 144 mm tall — the S0 frame is a common footprint for motor feeder panels. Required clearances: 70 mm above and below, 30 mm to the side, 0 mm forward and backward. No extra side gap needed if mounted against a panel wall. Terminals accept 1 to 10 mm² solid or stranded, up to 2×10 mm². Main contact screws are M4; use a Pozidriv size 2 screwdriver with a 5–6 mm diameter shaft.