Dimmer Switch Is a Mood-Changer
By T. Jeff Williams
One of the easiest ways to change the mood of a room is to vary the brightness, and that's easily done by installing a dimmer switch.
There are several different types of dimmer switches, including toggle-type, a dial-type, slide-action and touch-control. Regardless which one you choose, the switches all are installed in the same manner.
Be aware, however, that some dimmer switch bodies are larger than standard switches, and your existing switch box in the wall may be too cramped to fit it in. If that's the case, look around for a smaller dimmer switch.
Make Sure Power is Off
In starting this project, the first thing is to ensure there is no power to the switch you plan to change. At the service panel, turn off the breaker or remove the fuse that controls that switch circuit. You still need to double check that the power is off at the switch.
To check that power is off, first remove the switch plate by removing the two screws holding the plate to the switch. Next remove the two screws above and below the switch. Grasp the toggle without touching any bare wires or metal and pull the switch slightly out of the box.
Now use a circuit tester to ensure there is no power at the switch. The easiest way to test for power is with a no-contact tester. Simply touch one end of the tester to a wire, even if insulated, and the tester will buzz if power exists. If you are using a neon circuit tester, touch one bare lead to the copper grounding wire and the other lead to each screw on the switch. If the tester glows, there is still power at the switch. Go back to the service panel and turn off the correct breaker or fuse.
Remove the Old Switch
With power off, pull the switch completely out of the box. You will see two white wires joined by a wire nut. Leave them as they are. There will also be two black wires coming from the wall that are attached to two screws on the side of the switch. In some cases, one of the wires may be white with black tape or ink on it. This indicates it is a "hot" wire, meaning it carries power. Treat it just like a black wire. Turn the screws on the switch counter-clockwise to loosen them, and pull the wires free.
If the wires are pushed into the back of the old switch, use a small screw driver to push down in the slot next to the wires and pull the wires out at the same time. Or better, simply cut the wires next to the switch and throw that switch away. Those old push-in type switches are not reliable.
The ends of the wires that you removed from the old switch will be bent and crooked, so clip them off and then use your wire stripper to remove 3/8-inches of the insulation (see box below on wire strippers and other tools you will need).
Install Dimmer Switch
The new dimmer switch will have two black wires coming from the back. Twist the stranded dimmer switch wire around the end of a black wire coming from the wall and then screw on a wire nut. Yellow wire nuts are best for joining two 12-gauge or 14-gauge wires, standard sizes in residences. Connect the other dimmer switch wire to the other black wire in the same manner. It does not matter which wire from the switch goes to which wire from the wall.
If there is a green grounding wire on the dimmer switch, attach it to the green screw in the metal switch box. If you have plastic switch box, attach the green grounding wire to the bare copper grounding wires in the box with a yellow or tan wire nut.
Before you screw the dimmer switch to the electrical box, double check that all the wire nuts, including those on the white neutral wires, are screwed on tight.
Fold the wires in a Z-pattern and push them back into the electrical box. Attach the dimmer switch to the box with the two screws and then replace the wall plate.
A note on wall plates: If you installed a toggle or dial-type dimmer switch, your old switch plate will work. If you installed a slide-type or touch control dimmer, with rectangular faces, you will need a special wall plate, which are routinely available at any OSH store.
Turn the breaker or fuse back on and give your new dimmer switch a test run. If by any chance it does not work, turn the power back off and take it all apart so you can check that each wire connection is properly made.
Tools You Will Need:
Screwdrivers: You need two flathead and two Phillips screwdrivers, one large and one small, to cover most needs. The handles should be rubber, wood or plastic to provide insulation if a live wire is accidentally touched.
Circuit tester: There are two primary types for home use, the neon tester and the non-contact tester. With the neon tester, you touch one lead to either the metal switch box or a bare copper grounding wire, and the other lead to the screws on the side of the switch. If the neon light glows, there is power to the switch. Do not touch anything more until you return to the service entrance and turn off the correct breaker or fuse. The non-contact tester is very simple to use. Just touch one end to the side of the switch after you remove the cover plate and activate the tester. If it buzzes, there is power there.
Wire stripper: Similar to a pair of pliers, the stripper quickly and accurately strips insulation from the ends of electrical wires. Just put the wire in the hole according to the wire size you are using, usually 14-gauge or 12-gauge, clamp down with a little twist, and slide the insulation off.
Check your state and local codes before starting any project. Read product instructions carefully. Follow all safety precautions. Neither the contributor, OSH, nor any retailer can be held responsible for damages or injuries resulting from the use of this information.