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Re: Fan Wiring

A potentiometer IS NOT the same thing as a "dimmer switch" sold for dimming 
AC electric lighting. A "dimmer switch" is actually a combination of a 
potentiometer (pot) or rheostat and an electronic device known as a triac 
along with a few other components to make the circuit work. You absolutely 
do NOT want to use a pot to control the speed of an AC fan!!! VERY 
DANGEROUS! The small electronic potentiometers have ratings around 1/2 watt 
and are intended to control less than 10 volts or so. The rheostats you can 
buy at Radio shack are NOT POWER RHEOSTATS but are rather for low-voltage 
applications. They work fine for 12v DC fans but DO NOT use them with AC 
line voltage! And an important thing to remember about pots and rheostats: 
they work by putting some of the power into heat rather than the load (fan) 
to slow it down. They need some ventilation.

Someone else posted an idea to use a dimmer switch in a box with a cord to 
control your fan. This can work well. I suggest using a METAL box with 
cable clamps (probably sold as 1/2" NM cable clamps that fit into the 
knockouts in the box). The clamps will keep the wire from pulling loose. Be 
sure to connect the GREEN wire to the box with a screw so that it will be 
grounded. Some fans will not work properly when connected to a dimmer 
switch so if your fan acts strangely (loud humming, excessive heat, etc.) 
then don't try to slow it down with a dimmer.

You can use one of the snap-on plugs for "zip cord" with your fan's power 
lead if you are using one of the usual fan cords. Zip cord looks like two 
wires bonded together with a little seam in the middle. It's safer to use a 
plug than to try to properly seal the electrical connections..

BTW, you'll find it much easier to control the speed of a DC fan. There are 
also more DC fans that are built to run quietly to choose from, including 
the so-called "smart" fans that speed up automatically when the temperature 
increases. I posted some sources for these a little earlier this month on 
the list.


>My fan is a straight 120 AC fan you could plug into the wall, but it
>come with a plug.  It comes with bare wire ends and is intended to be
>included in a project.  I wired it into my hood before the ballast.
>However, the advice about using a dimmer switch from Home Depot may
>still be valid.  I wonder if a dimmer switch is really different from a
>potentiometer?  Does anyone know?