The Siemens 3RV1421-0AA10 is a SIRIUS circuit breaker specifically designed for transformer protection — a 3-pole device rated at 0.16 A continuous current with Trip Class 10, meaning it can handle the inrush of a small transformer without nuisance tripping while still providing short-circuit and overload protection downstream. Its breaking capacity is a flat 100 kA across the full voltage range from 240 V to 690 V AC — that means the same SCCR rating holds regardless of whether the panel is fed from a 400 V or 690 V supply, simplifying coordination studies. The device includes phase failure detection, so if one phase drops out on a three-phase transformer, the breaker trips — preventing single-phasing damage to the load.
The 0 mm backward clearance requirement means the breaker can be mounted flush against the back panel. Screw terminals on both the main and auxiliary circuits accept solid or stranded conductors: 2x 1–2.5 mm² or 2x 2.5–6 mm² per terminal, with AWG equivalents 2x 14–10. The front is IP20 and finger-safe, so it can be installed on a live busbar in a closed panel without additional shrouding.
The substance prohibition date of 01.05.2012 aligns with RoHS and REACH compliance timelines for this class. Surge voltage withstand is rated at 6 kV, and shock resistance at 25g for 11 ms — suitable for industrial environments with moderate vibration.