Project Guide

How to Install a Dimmer Switch

1
Choose a Dimmer Switch
A dimmer switch on a wall next to a door.

The first step in learning how to install a dimmer switch is choosing the best type for your needs. Allowing you to select just the right amount of lighting, as well as save on energy, dimmer switches come in a variety of styles and colors.


When choosing a dimmer switch for your home, you will want to determine three things: the type of light used with the dimmer, number of switches that control the light fixture and amount of lights connected to a single dimmer switch. 


  • Type of light: Dimmers are rated for specific types of lights. Selecting the wrong dimmer could mean the lights would flicker, stay on or simply not work. If you plan to use an LED bulb, you need to make sure you are selecting a LED dimmer, as LED run on a DC current. LED bulbs are also compatible  with smart dimmer switches. While LED will work with CFL switches, CFL dimmers are still recommended for these bulbs. Typically, incandescent and halogen bulbs work well with most dimmer switches, but it’s best to choose either halogen dimmers or incandescent dimmers according to the bulbs you’re using. Dimmer switches are not compatible with all fluorescent lights, so be sure to always double check the dimmer switch is rated for the specific bulb you choose.  
  • Number of switches: Dimmers come in two basic wiring configurations: standard single-pole dimmers and three-way dimmers. With a standard single-pole dimmer, a single switch controls the light. With a three-way dimmer, you can control a light with two switches. You will need a three-way dimmer and a three-way switch. This lets you dim from one location and turn the lights on and off from another. If only one switch controls the light, purchase a single-pole dimmer. If two switches control a single light or a group of lights, you will need a three-way dimmer. 
  • Amount of bulbs: Consider how many lights you will be connecting to the dimmer switch and add up their wattage. Check the rating on the dimmer switch you chose to ensure it can withstand the wattage you need. 


Tip: There are times when dimmer switches cannot replace basic switches. For instance, ordinary dimmer switches are not intended for use with most fluorescent lights or with most ceiling fans. The current fluctuations can burn out the motor. Consider these factors when wiring a dimmer switch.

2
Turn Off Power & Remove Old Switch
A person removing an old switch.
  • Turn off the power at the circuit breaker box. Confirm power is off by flipping the current switch on and off or test the circuit with a known working voltage tester, to ensure power isn’t reaching the circuit. 
  • Use a screwdriver to remove your existing wall plate and the screws mounting the switch to the wall box.
  • Gently pull the switch away from the wall. If you see a bundle of white wires in the back of the wall box, you can leave them in place.
  • If you are replacing a three-way switch, one wire will be connected to a screw that is colored differently or labeled “COMMON.” Note that this is different from the wire connected to the green screw, which is the ground wire. Tag the common wire with a piece of electrical tape to identify it when wiring the new dimmer.
  • Disconnect all wires from the old switch. If you are replacing an existing dimmer, you would need to unscrew the wire nuts around the switch wires and house wires.
3
Connect the New Dimmer Switch
A man connects the new dimmer switch to the outlet.

Here are the steps for wiring a single-pole dimmer switch:


  • If the house wires are bent, use a wire stripper to cut off the twisted ends. Remove 3/4 inch of casing from the end of the house wires if needed.
  • Connect the ground wire from your dimmer to a green or bare copper wire in the wall box. Twist the ends together clockwise and cap them using a wire connector nut.
  • Connect each dimmer wire to a house wire by gripping the wire ends with a pair of pliers and twisting them together. The wires from the dimmer will typically be black. The two house wires may be black, red or white with black marking. Tighten a wire nut over each pair of wire ends. If there is bare wire exposed, unscrew the wire connector, remove the wires, trim the ends of the wires with a wire cutter and then re-cap the wires.


Here are the steps for wiring a three-way dimmer switch:


  • If the house wires are bent, use a wire stripper to cut off the twisted ends. Remove 3/4 inch of casing from the end of the house wires and the dimmer switch wires, if needed.
  • Connect the ground wire from your dimmer to a green or bare copper wire in the wall box. Twist the ends together clockwise and cap them using a wire connector nut.
  • Connect the black dimmer wire to your tagged common wire and remove the electrical tape.
  • Connect the two remaining dimmer wires, called traveler wires, separately to each remaining wire in your wall box.
  • Use a screwdriver to mount your dimmer to the wall with the provided screws.
4
Replace the Wall Plate
A person is mounting their new dimmer switch wall plate.
  • Carefully tuck the wires back into the electrical outlet box.
  • Tighten the screws holding the dimmer to the electrical box.
  • If you are installing a dimmer that has a removable knob, remove the knob from the dimmer by gently pulling outward before attaching the wall plate.
  • If the dimmer has a separate wall plate, tighten the mounting screws that hold the wall plate to the switch. If you are using a wall plate with a screwless design, screw the wall plate adapter to the dimmer, and carefully snap the wall plate onto the adapter.
5
Turn Power Back On
A person touches the dimmer switch to test the power.
  • Once the wall plate has been successfully installed, return to your circuit breaker and turn the power back on. 
  • Test the dimmer to make sure it is working correctly.

Learning how to install a dimmer switch doesn't need to be complicated. Ready to start your project? The Home Depot delivers online orders when and where you need them.