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.
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.
Main contact screws are M4; use a Pozidriv size 2 bit or a 5–6 mm diameter screwdriver shaft.