Adding Three Phase Power To The Small Shop
by John Renzetti

On occasion I have seen high quality heavy duty woodworking machinery being offered and sold at a fraction of their acquisition price. The problem facing the small shop owner, either professional or amateur craftsman is that the machinery is usually powered by three phase motors. If three phase power is not already available, the cost of installation by the electric company could be prohibitive. Another option is to install a rotary phase converter. These are available as a complete unit or if desired, you can build a converter yourself. This article will cover the installation of a commercially available unit. It is not intended to replace or supersede the installation instructions that are included with a purchased unit.

I recently installed a Kay Industries Phasemaster converter in my home shop. The purpose was to provide three phase power to a jointer/planer whose smaller single phase motor was replaced by a larger three phase one. Also it will provide three phase power to another machine which will be delivered later.

Phase converters are rated by the maximum hp of the largest machine they will provide power for. For my machine (rated at 4kw) the Phasemaster Model MA-1 was sufficient. According to the literature I could run this machine and hook up other machines as long as the total hp was not greater than 20hp If the motor was any larger I would have required the next higher model.

Once the largest hp is known the next thing is to determine the electrical requirements. For this converter I needed a dedicated 40a circuit using #8-2 copper. If the distance from the panel to the converter is greater than 40ft then Kay recommends the next higher wire size to avoid voltage drop. Since I had a 100a subpanel in the shop voltage drop was not a problem. I did have to add an additional circuit and ran the wire through rigid conduit. I used ¾” which was minimal. I would recommend 1.” Between the phase converter and the panel box you need to install a fused disconnect. The fuses should be 30a time delay. The purpose of the box is for voltage protection as well as provide a means of turning the phase converter off when not in use. This setup also prevents single phase power from going into the machine, since no power can go to the machine unless the converter is powered. With power applied, the converter will run at idle, drawing about 3amps. While at idle the noise for me is minimal.

Placement of the converter is optional. I placed mine close to the machines, which makes the wiring connections from the line voltage to the converter and from the converter to the machines relatively easy.

The way I did the wiring here was to run the line voltage to a large junction box. Use a 6x6 or a bit larger, the standard 4”+ box is too small. The wires (8-2 and 10-4) can be connected using wire nuts but a better way would be terminal blocks. Before doing this you should consult with an electrician, or if in doubt have the electrician do the installation. The wiring is relatively simple, the line voltage, black and white wires and connected to the L-1 and L-2 lines going into and out of the phase converter. At the junction box I have the 8-2 coming in through the conduit, The converter is connected using 8-4MC (metalic cable) the black and white wires to the black and white wires of the 8-2 line voltage, the green is the ground wire. Also connected to the junction box and going to the machines is 10-4SO cable. The white and black wires are connected to the line voltage and the 8-4MC. Green is ground, and the red wire is used as the T-3 manufactured three phase. This is connected to the red wire coming out of the converter. This wire provides the third phase to the machinery.

Once the converter is properly wired operation is very simple. Power up the converter by flipping the lever of the quick disconnect to “on” , the converter powers up is less than two seconds. It runs at idle, producing very little noise. Starting your machinery is as always, just push the start button. It powers up instantly.

This probably doesn’t cover all aspects of a converter installation. If anyone reading this has any other questions on what I did to install the three phase power please feel free to E-mail me or ask on the Forum.

John Renzetti - 10/5/98