Transformer-protection circuit breaker with 100 kA interrupting capacity
The Siemens SIRIUS 3RV2411-1KA20 is a circuit breaker designed specifically for transformer protection, carrying a 100 kA breaking capacity at 400 V — that means it can safely interrupt a fault current up to 100,000 A on the secondary side of a distribution transformer without cascading upstream. The Trip Class 10 thermal overload curve matches the inrush profile of transformers and motor starters, tripping fast enough to protect windings but not so fast that normal energization peaks nuisance-trip the line.
Backup fuse coordination and operating limits
When installed upstream of a transformer, the breaker requires backup gL/gG fuses sized according to the line voltage: 63 A at 400 V, 50 A at 500 V, and 40 A at 690 V. These fuse ratings limit the let-through energy so the breaker's internal contacts survive a bolted fault. The rated operational voltage spans 20 to 690 V, covering most low-voltage distribution systems from control transformers to 690 V industrial mains. The maximum switching frequency under AC-3 or AC-3e duty is 15 operations per hour — fine for transformer switching or infrequent motor starting, but not for high-cycling applications like a welder or press.