The Siemens 3RV1421-1GA38-1KT0 is a SIRIUS-branded circuit breaker specifically designed for transformer protection. Breaking capacity is 100 kA at 240 V, 400 V, and 500 V AC, dropping to 6 kA at 690 V AC — that covers most industrial distribution panels where the transformer primary is fed from a high-fault bus.
Width is 45 mm, height 97 mm, depth 96 mm — fits a standard 45 mm-wide DIN-rail footprint. Screw-type terminals on the main circuit accept 2x (0.25... 2.5 mm²) solid or stranded; auxiliary and control circuit uses spring-loaded terminals with the same wire range. IP20 on the front, so it's protected against finger contact once the panel door is closed.
The integrated auxiliary switch is rated 1 A at 24 V, 0.15 A at 60 V, and 0.5 A at 230 V — enough to drive a PLC input or a small relay in the control circuit.