Installing a Dimmer Switch

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.

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.

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.

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).

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.

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.