Installing a Dimmer Switch

Intro

You can replace a switch for any incandescent light with a dimmer. Fans and fluorescent lights use special dimmers.

You can replace one of the three-way switches in a circuit with a three-way dimmer.

A dimmer can control line-voltage halogen lights, but a dimmer won't work with low-voltage halogens.

A dimmer switch rated for 600 watts can handle most ceiling lights. For a chandelier, add up the wattage of all the bulbs; you may need a dimmer with a higher rating.

Checklist

Time
About 20 minutes to replace an on-off switch with a dimmer

Tools
Screwdriver, side cutters, voltage tester, lineman's pliers, strippers

Skills
Stripping and splicing wire

Prep
Lay a towel or small drop cloth on the surface below the switch.

Materials
Dimmer switch, wire for pigtails, wire nuts (they may come with the switch), electrician's tape

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Step 1

Shut off power to the circuit. Remove the cover plate, pull the switch out, and test to make sure there is no power. Loosen the terminal screws and remove the wires. Cut and restrip the wires.

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Step 2

If two cables enter the box, splice the white wires together. Splice each black lead to a black wire on the dimmer. Connect the grounds.

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Step 3

Fold the wires back as you push the dimmer into the box. The dimmer is bulkier than a regular switch, so the box may be crowded.

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What If There's Only One Cable?

If only one cable enters the box, splice one lead to the black wire and one lead to the white wire (which should be marked with black).

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Installing a Dimmer in a One-Switch Circuit

On a one-switch circuit, if the dimmer is the only switch controlling the light, the dimmer has one green and two black wires or a green, a black, and a red. Connect the green wire to a pigtail that grounds the box and to the green or bare wire entering the box. If both wires are black, connect each to one of the remaining unconnected wires. If the wires are red and black, check the directions for the dimmer switch. One needs to connect to the hot wire, the other to the light.

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Installing a Dimmer in a Two-Switch Circuit

If the dimmer and a three-way switch control the circuit, the dimmer has a common wire that is most likely black. The two travelers are the same color as each other, usually red. If there's any confusion check the directions that come with the dimmer. Then check to see which wire in the switch box is hot. Connect the hot wire to the common wire. Connect the ground to ground and connect the remaining two dimmer wires to the remaining unconnected wires.

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