Transformer-protection circuit breaker, 16 A, SIRIUS S2
The Siemens 3RV5431-4AA10 is a 3-pole SIRIUS circuit breaker purpose-designed for transformer protection, with a rated operational current of 16 A and a rated insulation voltage of 690 V. It carries a Class 10 trip characteristic, meaning the thermal overload release responds within 10 seconds at 7.2× the current setting — fast enough to protect a transformer winding from sustained overcurrent without nuisance-tripping on inrush. The magnetic short-circuit trip handles the high fault currents a transformer primary can see on a phase-to-phase bolted fault. Rated at 16 A in AC-3 duty at 400 V, this breaker switches motor loads up to that current, but its primary job is transformer primary-side protection where the inrush profile differs from a motor start. The S2 frame size keeps the unit compact enough for dense panel layouts while still accommodating screw-type box terminals that accept up to 35 mm² solid or 25 mm² finely stranded wire.
The 55 mm width and 149 mm depth fit standard S2 panel cutouts; clearance requirements are 50 mm upward, 50 mm downward, 140 mm forward, and 30 mm at the sides. Connections are top and bottom for the main circuit, with screw terminals torqued to 3–4.5 N·m. Operating temperature range is –20 to +60 °C with 10–95 % relative humidity, so it handles unconditioned industrial enclosures. Installation altitude is limited to 2 000 m above sea level without derating.
Electrical and environmental ratings
Rated operational voltage 690 V AC at 50/60 Hz. Shock resistance per IEC 60068-2-27 is 25 g for 11 ms. Typical power loss is 12 W total. The breaker provides both thermal overload protection (Class 10) and magnetic short-circuit protection in one unit.