How to Install a Dimmer Switch (page 2 of 2)

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How to Install a Dimmer Switch-Installation

Test Your Ground Before You Connect It
New dimmers have either a green grounding wire or a green ground screw that you’ll have to connect to a grounding source if one is available. Houses wired with plastic-sheathed cable almost always have bare copper ground wires that you’ll connect to the dimmer. But test first using the procedure shown in Photo 3 to verify that the wire is connected to a ground.

Some wiring systems, like ours, rely on metal conduit for the ground. If you have one of these systems, Photo 3 shows how to test the metal box to verify that it’s grounded. If it is, attach a short ground wire to the metal box with either a metal grounding clip or a green grounding screw screwed into the threaded hole in the back of the box. Then connect it to the dimmer.

If testing reveals your box isn’t grounded, you can still install the dimmer, but you must use a plastic cover plate and make sure no bare metal parts are exposed.

Caution: if you have aluminum wiring, don’t mess with it! Call in a licensed pro who’s certified to work with it. This wiring is dull gray, not the dull orange that’s characteristic of copper.

The Easy Part Is Installing the Dimmer
Some dimmers, like the one we’re installing, have stranded wires attached. Photos 7 and 8 show how to install this type of dimmer. Others have screw terminals instead. For these, strip 3/4 in. of the insulated covering from the “common” wires in the box and bend a loop in each with a needle-nose pliers. Place the loop clockwise around the screw terminals and close the loop around the screws with the needle-nose pliers. Then tighten the screws.

It doesn’t matter if you reverse the two switch wires to a single-pole dimmer. But if you’re replacing a three-way switch with a three-way dimmer, label the “common” wire (it’ll be labeled on the old switch) when you remove the old switch so you can connect it to the “common” terminal on the dimmer.

In most cases, the two switch wires will be some color other than green or white, usually black. But one of the wires may be white if your house is wired with non-metallic sheathed cable (one brand is Romex). Put a wrap of black tape around the white conductor to label it as a hot wire.

Caution : call an electrician if the original switch is connected to two white wires. This may indicate a dangerous switched neutral.

Buying Dimmers
If the switch you’re replacing is the only switch controlling the light, buy a standard single-pole dimmer ($5 to $30). If the light can be switched on and off from two or more switches, buy a three-way dimmer switch. But you won’t be able to dim the lights from every switch location unless you buy a set of special dimmers (about $70 per pair) with advanced electronics and install one at each switch location.

Most dimmers are designed to handle 600 watts. Add up the wattage of all the light bulbs you’ll be dimming. Then read the dimmer package to make sure it can handle the load. Heavy-duty 1,000- and 1,500-watt dimmers are also readily available. Read the package if you’ll be installing dimmers side by side in the same electrical box because the wattage rating is reduced to compensate for extra heat buildup.

Finally, you have to use a special device, not a dimmer, to control the speed of ceiling fans and motors. Most fluorescent lights can’t be dimmed without altering the fixture.