What it is and what it does
The Siemens 3RV6421-4BA10 is a SIRIUS circuit breaker specifically designed for transformer protection. It combines a thermal overload release (Class 10 trip) with a magnetic short-circuit trip in a single 3-pole device, size S0. Rated operational current is 20 A at AC-3 duty on 400 V, with a maximum rated voltage of 690 V at 50/60 Hz. The Class 10 trip characteristic means it will trip within 10 seconds at 7.2× rated current — matching the inrush profile of a transformer primary. Mounts on 35 mm DIN rail per DIN EN 60715 via screw and snap-on fastening. Any mounting position is permitted. Clearance requirements: 50 mm above and below, 30 mm to the side, 0 mm forward and backward — useful when packing multiple breakers in a panel.
Key ratings in context
Power loss is 8 W typical — a figure to factor into panel thermal budgeting when grouping several breakers in a confined enclosure. Screw-type terminals accept 2×(1–2.5 mm²) solid/stranded or 2×(2.5–10 mm²) solid, with tightening torque 2–2.5 N·m. AWG equivalents: 2×(16–12) or 2×(14–8). Top and bottom entry for main circuit connections. Rated surge voltage resistance is 6 kV; shock resistance 25 g / 11 ms per IEC 60068-2-27. Operating temperature range –20 to +60 °C, storage –50 to +80 °C. Maximum installation altitude 2000 m. Substance prohibitance date 05/01/2012 indicates RoHS compliance from that date forward.