The Siemens 3RV2821-4CD10 is a SIRIUS circuit breaker in size S0, designed specifically for transformer protection and certified to UL 489 and CSA C22.2 No.5. It mounts on 35 mm DIN rail per DIN EN 50022 using either screws or the snap-on feature, and can be oriented in any position — useful when fitting into a crowded panel where vertical clearance is tight.
Breaking capacity and coordination
At 400 V AC this breaker interrupts 55 kA (IEC) and 25 kA (UL), so it handles high-fault installations without cascading upstream. The 100 kA rating at 240 V AC covers the common North American service entrance range. For backup fuse coordination the manufacturer specifies gG fuses: 63 A at 400 V, 50 A at 500 V, and 50 A at 690 V — match these when the available fault current exceeds the breaker's standalone rating.
Motor and load sizing
Rated for 5.5 kW at 230 V, this breaker suits small-to-medium motor loads on 230 V three-phase systems. The AC-3e switching frequency maxes at 15 operations per hour — fine for pump or compressor starts, not for high-cycling servo or jogging duty. The voltage range spans 20 to 690 V, covering most low-voltage industrial supplies.
Panel integration and wiring
The 45 mm width (3 module spaces on a standard DIN rail) and 97 mm depth fit a compact panel layout. Clearance requirements: 70 mm above and below, 30 mm to the sides, zero forward or backward — so you can mount it flush against a backplate. Screw terminals accept 1 to 10 mm² solid or stranded, up to 2×10 mm². Main contact screws are M4; use a Pozidriv size 2 bit or a 5–6 mm diameter screwdriver shaft.