How-To Geek

How to Replace a Light Switch with a Dimmer Switch

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If you want better control over how bright or dim your lights get, installing a dimmer switch is a great way to make that happen, especially if you want to adjust them regularly. Here’s how to replace a regular light switch with a dimmer switch.

Warning: This is a project for a confident DIYer. There’s no shame in getting someone else to do the actual wiring for you if you lack the skill or knowledge to do so. If you read the beginning of this article and immediately visualized how to do it based on past experience wiring switches and outlets, you’re probably good. If you opened the article not sure how exactly we were going to pull this trick off, it’s time to call in that wiring-savvy friend or electrician. Also note that it may be against the law, code, or regulations to do this without a permit, or it might void your insurance or warranty. Check your local regulations before continuing.

What You’ll Need

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There’s actually not a whole lot you need for this project. The absolute must-have tools include a pair of needle-nose pliers, a flat-head screwdriver, and a Phillips-head screwdriver.

Some optional—but very handy—tools include some combination pliers, a wire stripper tool (in case you need to cut wire or strip off wire housings), a voltage tester, and a power drill.

Also make sure that the light bulb you’re using with the dimmer switch is dimmable. Most CFL bulbs and cheaper LED bulbs are non-dimmable, meaning that if you use a dimmer switch with them, they’ll just flicker until you give them full power. So when you’re shopping for light bulbs, make sure that they can be used with dimmer switches—it should say on the packaging.

Lastly, you’ll need a dimmer switch, and there are many different styles to choose from. Personally, I like this one from Lutron, and it’s the one I’m using in this tutorial. Don’t forget the new faceplate either.

Step One: Turn Off the Power

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This is one of the most important steps and it should be done before anything else. Go to your breaker box and cut off the power to the room where you’ll be changing out the light switch.

A great way to know if you turned off the correct breaker is to turn on the light switch before cutting the power. If the light that’s controlled by the light switch turns off, then you know you’ve switched off the correct breaker.

Step Two: Remove the Existing Light Switch

Start by taking your flat-head screwdriver and remove the two screws holding the faceplate on.

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You can then pull the faceplate right off. At this point, use a voltage tester to see if the power is truly off to the light switch before you go any further.

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Next, take your Phillips-head screwdriver or power drill and remove the two screws that hold the light switch onto the junction box. There will be one on top and one on the bottom.

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Once those screws are removed, take your fingers and grab hold of the the tabs on the top and bottom of the switch to pull it out of the junction box. This exposes more of the wires and makes it easier to work on.

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Take a look at the wiring configuration of the light switch. You’ll notice that there are two black wires connected to the switch, as well as a bare copper wire, which is the ground wire. Further back in the box, you’ll also notice two white wires that are tied together with a wire nut. (If the colors in your wall are different, make note of which are which, to ensure you connect everything properly.)

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As briefly explained above, the black wires are the power (or “hot”) wires and the white wires are the neutral (or “return”) wires. Electricity flows through the hot wire, entering the switch and then into the light fixture, and then returns back through the neutral wire. Turning off the switch simply disconnects the power wire from the light fixture, cutting off power from your lights.

Start off by taking your screwdriver and removing the two black wires attached to the light switch. Don’t worry about which black wire goes where, because they’re interchangeable.

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Lastly, remove the ground wire from the green screw.

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Step Three: Prepare Your Wires for the Dimmer Switch

Now that the light switch is completely removed, you’ll need to prepare for the installation of the dimmer switch.

Grab your needle-nose pliers and straighten out the black and ground wires. Since they’re bent like hooks from the old switch, they’ll need to be straightened out so that you can attach wire nuts to them when you hook up the dimmer switch.

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And that’s all the preparation we need for this. We’re now ready to install the dimmer switch.

Step Four: Install the Dimmer Switch

Your dimmer switch will come with wire nuts and a couple of screws. The switch itself will have two black wires and one green (ground) wire. At this point, it’s just a matter of matching the wires between the switch and the junction box and wiring it up.

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Start by taking the green wire and connect it to the bare copper wire. Do this by placing the two wires together side-by-side with the ends matching and screw the wire nut on clockwise like you’re turning a small knob. You’ll want to crank it until it’s very snug to prevent the wires from popping back out.

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Next, do the same thing with the two black wires. Again, it doesn’t matter which black wire goes with which, since they’re interchangeable. This is what it will look like when it’s all wired up:

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Next, you’ll need to stuff all those wires back into the junction box while still making room for the dimmer switch, which can be tricky since the dimmer switch is a lot thicker than a traditional light switch. Don’t be afraid to get rough with the wires and bend them back into the box as far as they’ll go.

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Place the dimmer switch completely into the junction box and use the two included screws to secure the switch to the box.

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Once the switch is secured, take the faceplate and place it over the switch. Use your flat-head screwdriver and screw the faceplate in with the two included screws.

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The dimmer switch is now installed and ready to go. Be sure to turn the power back on and test it out to make sure it fully works.

Craig Lloyd is TIME Magazine's 2006 Person of the Year, as well as a mediocre gamer, aviation geek, baseball fan, motorcyclist, and a proud introvert. He began his career as a young, naive teenager tinkering around with the family computer and has since blossomed into the beautiful geek he is today.

  • Published 01/5/17

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