How to Install a Dimmer Switch

A man turns a dimmer switch.
What You'll Need
Phillips and slotted screwdrivers
Wire stripper
Wire cutter
Electrical tape
Voltage tester
Dimmer switch
Dimmer wall plate
Wire connectors

A good dimmer switch can be a real game-changer in any room. But installing a dimmer switch is a little more involved than simply swapping out a few wires. From removing the old light switch to correctly wiring the new unit, here is a quick guide on how to install a dimmer switch in your home.

Step 1 - Turn Off Power

You always want to turn off the power at the main breaker whenever you do electrical work around the house. After you switch off the breaker, make sure the power is off by flipping on the old light switch. Do not proceed until the power is off.

Step 2 - Remove Old Unit

With the power off, use your screwdriver to take off the old switch cover. Two screws typically hold the switch in place. Once the plate is off, remove the two screws connecting the switch to the electrical box. At this point, you should be able to pull the switch out of the wall. Use your voltage tester to double check that the power is off before moving forward.

Step 3 - Disconnect Wires

A man works on a dimmer switch.

Make a note of the color of wires and where each one is attached — this will tell you which wires are power, ground, and neutral. Use the Phillips screwdriver to loosen the screws on the side of the switch that hold the wires in place. Once the screws are loose, the wires should come out easily. To help keep the wires organized, bend them off to the side of the outlet box. If there is a ground wire attached to the switch, it should be removed last. If you cannot remove the wires from the screw, use a pair of pliers to pull them free.

Step 4 - Prepare Old Wires

Properly prepare the old wires for the new device by using a wire cutter to trim off the old twisted ends. Then cut ¾ inch worth of insulation from the end using the wire stripper. This should expose the copper wire. Repeat this process with all of the wires that were connected to the old switch.

Step 5 - Connect Stranded-Wire Dimmer

A stranded-wire dimmer is a model that already has wires coming out of the unit. Referencing your notes from earlier, connect each wire to its corresponding wire via a plastic wire connector. Before you tighten down the connector, twist the correct wires together using pliers. You should twist them in a clockwise direction so that they do not come under when you tighten down the connector.

When using the wire connectors, you want to make sure that you cannot see any exposed wire after you tighten down the connector. If copper is visible, simply remove the connector, trim off some of the wire, and tighten it back down. You also may need to trim the old wire more if you cannot fit all of the wires back in the box.

Step 6 - Connect Traditional Dimmer

A row of dimmer switches.

Some dimmers do not feature any stranded wires and come equipped with screw terminals, like most light switches. For these dimmers, follow the instructions that came with the dimmer when attaching the wires to the correct terminal. In most cases, three wires are needed to complete the setup: power, neutral, and ground. Double check that you connected the wires correctly before proceeding to the next step. When attaching the wires, bend them with the pliers to create a loop. Then place the loop on the screw in a clockwise direction and tighten them up.

Step 7 - Finish Dimmer Install

With the wires connected, push the dimmer unit inside the receptacle box and screw it in place. Make sure all of the wires are still firmly in place before tightening the screws. If you need to, gently fold some of the wires to get the dimmer switch in place. Once the dimmer switch is securely connected to the box, install the switch plate that came with the unit. You may need to tighten or loosen the screws to get the best fit.

Step 8 - Test The Dimmer Switch

Once the new dimmer switch is installed, you can turn on the power at the breaker. With power restored, test the dimmer switch and make sure all of the lights are functioning properly. If the switch does not work, it is possible that you do not have the right bulbs for dimming. Not every light bulb is capable of dimming, so make sure you purchase one that is rated for this purpose before installing the dimmer switch.

Dimmer Switch Tips

A dimmer switch and regular light switches.

There are several things you should know before you buy a dimmer switch. If the light only has one switch controlling it, then purchase a single-pole dimmer. If there are multiple switches for the same light, then you need a three-way dimmer. The downside to a three-way switch is that not all switches will be able to dim the lights, unless you purchase a specialty set. Further, dimmers are typically made to take up to 600 watts. Make sure your dimmer can handle that load by adding up the wattage of the lights hooked up to the dimmer. If the total wattage is over 600, then you should purchase a dimmer that is rated for heavier loads.