Before shopping for a replacement switch, determine the exact location where you’re planning to install it. If it’s the only switch for that light, you’ll need to purchase a single pole switch. If there are two switches controlling it, you’ll need a 3-way. You can install the 3-way dimmer on either of the switches, but not both. Most dimmer switches are a little boxier and have the wires already built in. So make sure the new switch will properly fit where the old one was. There are several different types of dimmers such as sliders and rotary and many different styles and colors. So choose the one that best fits your needs and matches your decor. * Please note that LED and dimmable CFL bulbs will require a dimmer that’s made for those types of bulbs.
Before doing any electrical work, always turn off the power at the breaker box and clearly mark it out of service so no one else will turn the breaker back on while you’re working. Test the switch to make sure you’ve located the correct circuit for the light.
Now, take off the cover plate with a screwdriver and use a non-contact voltage detector to confirm that the power is off to all of the switches in the box. If no current is detected, remove the screws attaching the switch to the electrical box, then pull it out. Unscrew the wires from the terminals and mark if needed. If you need more room on the wires to make the connections, trim back about a half inch of insulation with a pair of wire strippers. For the single pole house wires, you should have one black wire and the other is usually red or has black markings. You’ll also have a bare copper ground wire. Connect the ground wire to the green ground on the dimmer switch by twisting the two together and screwing on a wire nut. Now connect the red wire from the house to one of the black wires on the dimmer switch. It doesn’t matter which black wire you choose. Finally, connect the black house wire to the other black wire, screwing on a wire nut to secure the connection.
Now wrap some electrical tape around each of the wire nuts to keep them from coming off as you finish the job. For 3-way switches, there should be three house wires not including the ground wire in the electrical box. The hot wire is connected to the black screw. It carries the power to the switch and should be labeled before disconnecting. The other two wires are called traveler wires because they travel between the two switches. These are interchangeable. Start by wiring the bare ground wire from the house to the green ground wire on the 3-way switch.
Screw on a wire nut and tighten it down. Then attach the two traveler wires from the switch, which are often red, to the two traveler wires from the house and add wire nuts. Now connect the black wire from the three-way switch to the black wire from the house. Finally, wrap electrical tape around all of the wire nuts to keep the connections from coming loose. Once all the connections are made, carefully push the wires back into the box. Since dimmer switches have more bulk, you may need to move things around to create space. In some cases, you may need to install a larger box to accommodate the additional wiring. Attach the switch to the electrical box with a screwdriver.
Now, turn the power back on and test out the dimmer switch to make sure everything’s working properly. As long as it functions correctly, replace the cover plate but be careful not to tighten the small screws too tightly or the pressure could crack the plate. Your dimmer switch will help set the mood and save energy at the same time.
As found on Youtube