3 Phase 400 VAC 6 A Variac


I bought this 6 A variac stack as advertised for 6A. But the physical size suggests it could be a 10A model as well. There is no part numbers or data shields to go by. Variacs are usually rated to be able to handle 200% overload for up to 5 minutes and 300% overload up to 1 minute.

As the lids and housing was missing, it needed to get built into a new enclosure.


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The variacs are only rated for 220 VAC, so star connection of the 3 variacs for 3 phased 400 VAC is needed. If the variacs was rated for 400 VAC each, they could have been connected in triangle.

There is no feedback of the real voltage and current measure, only the values of the dial. Since it is rated for 220 VAC and there is 230 VAC from phase to neutral in Denmark, there will be a difference. Measurement of all 3 phase-to-phase voltages and currents will be installed in the top panel.


Variac3x Transpower Vario Transformer. 0 – 220 VAC at 6 A
ConnectionStar connection for 3×400 VAC input and 0-400 VAC output
MetersAD101-22VAMS combined AC50-500VAC / 0-100A meter


Mains voltage schematic with 6 A variac star connection, voltage measurement and current transformers are shown.

6 A Variac Stack Construction

24th September 2016

I reused a old enclosure from a 20 kVA UPS system that I had from the junk yard. I had to saw it up in smaller pieces, to bring down weight and get a smaller enclosure.

6th May 2022

A good 5½ years have passed where this project was on hold due to moving, family, job and all those kind of things 🙂

In the meantime I had ordered some combined digital voltage and current meters from ebay. It is a AD101-22VAMS front panel meter with a 22.5 mm mounting hole. It is self supplied through the voltage measurement, why it will not work below 50 VAC. It is rated for 50-500 VAC and 0-100A. The wiring is pretty straight forward, as there is only the voltage and current measurements.

The variac was tested with a 3×400 VAC 9 kW space heater. With the variac set for 400 VAC, the current draw was around 12 A. this gives a total 3 phased power consumption around 8.2 kW.

The finished variac has its wire harness, front panel and one side with cable feedthroughs. The remaining four panels will be made once I have sourced some scrap yard materials in the right size.


The enclosure could be a few centimeters smaller, to bring down overall weight. The reused frame is quite heavy as its a pure steel frame made to carry a much heavier load. But it was free and repurposing is much better for the environment than melting and production of new materials.


6th May 2022

Construction, explanation and test video.