Ask Jon Eakes

Last Updated: Wednesday, September 15th, 1999, Created: Wednesday, September 15th, 1999

Power Tool speed controls: do's and don'ts

In this segment on my TV show, I demonstrated that a light dimmer switch should not be used as a speed control for a motor. Light dimmers drop the voltage and that drops the power supplied as well. Motor speed controls drop the amperage not the voltage, which gives much more power to the slower running motor. In fact, if you run a motor at less than 90 volts, especially if it is under load, you will probably burn it out. That is precisely what happens on the end of a very long extension cord. If your saw or drill is running slow or under powered on a long or undersized extension cord, you are asking for motor burnout.

If you look carefully at the hardware store there are dimmer switches for incandescent lights, different dimmer switches for some fluorescent lights with electronic ballast, different dimmer switches for halogen lights and totally different speed control switches for ceiling fan controls -- and they all look alike. Read the packages carefully!

Keywords: Controls, Electrical, Power Tools

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