Transformer-protection circuit breaker, 22 A, Class 10
The Siemens 3RV6421-4CA10 is a SIRIUS-brand circuit breaker specifically designed for transformer protection, not general motor starting. Its 22 A rated operational current (AC-3 at 400 V) and Trip Class 10 thermal-magnetic release mean it clears overloads on inrush-heavy transformer loads — the magnetic short-circuit trip handles faults, while the thermal element rides through the magnetizing inrush without nuisance tripping. The S0 frame size keeps the footprint compact at 45 mm wide, 97 mm tall, 96 mm deep — fits standard 35 mm DIN rail per DIN EN 60715, screw or snap-on mount, any position.
The S0 size leaves 50 mm clearance upward and downward, 30 mm to the side — no forward or backward clearance needed. Panel integration is straightforward: wire top and bottom with screw terminals accepting 2x (1…2.5 mm²) solid/stranded or 2x (2.5…10 mm²) solid; torque to 2…2.5 N·m. Ambient operating range -20 to +60 °C, 10-95% RH non-condensing. Installation altitude up to 2000 m. Shock rated 25 g / 11 ms per IEC 60068-2-27 — suitable for panel-mounted applications in industrial environments.
RoHS compliance date marked 05/01/2012. No UL, CSA, or CE marks appear in the spec record — verify with your quality team for the target jurisdiction.
The magnetic short-circuit release handles fault clearing; the product explicitly includes short-circuit protection (yes). Rated operational current 22 A at AC-3 duty (400 V) is the switching current for motor-like loads; for transformer protection the continuous current rating governs. Power loss typical 8 W total — factor into enclosure thermal calculations.