Transformer-protection circuit breaker from the SIRIUS family
The Siemens 3RV2431-4SA10 is a SIRIUS-brand circuit breaker specifically designed for transformer protection, with a Trip Class 10 characteristic and phase failure detection built in. It mounts on 35 mm DIN rail per DIN EN 60715 via screw or snap-on fastening, and accepts screw-type terminals for the main current circuit — up to 2x 25 mm² or 1x 35 mm² solid or stranded. Breaking capacity is rated 100 kA at 240 VAC, 65 kA at 400 VAC, 6 kA at 500 VAC, and 3 kA at 690 VAC. Motor horsepower ratings span 1.5 hp at 110/120 V up to 15 hp at 575/600 V.
Phase failure detection is integrated, so a lost phase on the supply side will trip the breaker rather than letting the transformer or motor single-phase and overheat. At 400 VAC the rating drops to 65 kA, still sufficient for most industrial panel feeds. The 3 kA at 690 VAC covers the high-voltage end for special transformer primaries.