How To Install a Dimmer Switch

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Estimated Time: 
30 minutes (for single pole switches)
Add Ambiance with a Light Dimmer


If you've never had a dimmer switch on any of your lighting, you're in for a treat. This easy-to-install device will add ambiance to every room in your house. Romantic dinners and soothing spa-like bubble baths can become an everyday event! Plus, dimmers are inexpensive—usually $12 to $20. The one we installed in Ellen's new condo was around $15.

SAFETY TIP!: Dimmers cannot be used on fluorescent lighting! They should also not be used on ceiling fans unless you specifically get a dimmer made for a fan/light combo.

And finally, before you remove your old switch, you first need to know what type of switch you are dealing with.

Here's a rundown:

Single-Pole Switch: This is a switch in which the electrical wires only affect one (1) light and do not continue on to other switches or receptacles.

Three-Way Switch: This type of switch works in pairs to control a light from two different locations. For example, you can turn on one light fixture from both ends of your hallway. We don't recommend installing a dimmer switch here, but if you do, don't install more than one dimmer—the other needs to be a toggle switch (the basic "on-off" switch we're all used to).

Four-Way Switches: These are rare, but are sometimes found in very large rooms. They are used in combination with a pair of 3 way switches to control lights from three or more locations.

How do I know what Type of Switch I Have?

Identifying your switch type is easy—just count the screws! Single-pole switches have two screw terminals, Three-way switches have three screw terminals, four-ways have four screw terminals. (Don't confuse the terminals with the ground screw-which will be located off by itself, not paired with a terminal)

SAFETY TIP!: Okay, another safety tip. A rule of thumb is not to install a dimmer switch that is connected to a receptacle (plug, or electrical outlet) as you can blow out certain things like a vacuum if you don't have the switch up to maximum power.

Before we get started, make sure the new dimmer switch is rated for the total wattage of the fixture. A good example would be a chandelier with five 100-watt bulbs would be too much for a 400-watt dimmer. This information is generally found on the packaging of the dimmer switch. If this is for a ceiling fan, then don't use a standard dimmer or you can burn out the motor of the fan. As we mentioned above, there is a special dimmer switch for ceiling fans. In fact, there are many choices in the arena of dimmers, so take your time and don't be afraid to ask questions. Also, be aware that most dimmers do not come with the matching face plates. So make sure you pick these up too, to avoid another trip to the hardware store.

Project Steps

Now we're ready!

Our first rule before doing anything electrical is turning the power off. First thing's first-make sure to turn off the circuit breaker that feeds that switch. If your circuit breakers aren't labeled, you'll have flip these on and off one at a time to see which one goes to which switch (or set of switches). It's best to do this with someone else in the other room who will call out when the light goes off. Turn it off (and label it now that you know which one it is). If you're working alone, be sure to either lock the breaker box, or put a note telling anyone who might come home and inadvertently turn the power back on that you're currently working on the electrical.

Step 1

Start by removing the face plate. Then, use an electrical tester (like a penlight tester) to make 100% certain there is no power coming to the line. Once you're sure, remove the screws from the top and bottom of the old toggle switch. Now pull the entire existing switch unit out of the junction box (the junction box is the plastic or metal box installed inside the wall that holds the switch in place. You'll see the wires from the switch box connected to wires coming from the wall. Unscrew the plastic wire caps and untwist the wires. Remove the old switch and discard.

Step 2

If the ends of the house wires are corroded, you can trim the wire a little and then use a wire stripper to strip off about 3/8" of the insulation. This will give you a clean piece of wire for the new connection to the dimmer. If the wire looks okay, you can leave it as is.

Step 3


Next we'll connect the wires from the new switch to the house wiring. Review the instructions that came with your new switch again. Often, it's as simple as matching like-colored wires (e.g. black to black and white to white) together. Unfortunately, in some homes, there is no universal code for the color of the wiring. Hot wires are usually black but can be red (ours was) and neutral wires are usually white, but can be blue, or as in our case yellow. We used a tester to verify which was which, i.e. that our home's hot wire was red and the neutral yellow.

Connect the tips of the wires by twisting them together and screwing on a plastic wire cap (most dimmer switches will include these in the package). Make sure that the bare wires are completely encased in the wire nut and don't slide off easily.

Jane Tip: In some older homes, there is no color variation of the electrical wires. So, you may want to begin by studying how your current toggle switch is connected and use that as your guide. If you've already removed the old switch and can't remember how it was connected, use your electrical tester to help guide you toward the "hot" wire (or load). If you happen to put the wrong wires together, there is a good chance you will blow out the dimmer switch and need to buy a new one, so we suggest getting it right the first time.

Step 4

The neutral wires should be connected next (in our case it was a blue wire from the switch to a yellow, neutral wire from the house). Cap with a wire nut as well. Use electrical tape to wrap around the base of the connection if you notice that there is any copper wire still exposed.

Step 5

If your house wiring has ground wires (usually green, found in newer houses), tie them together too. Ground wires are there mainly in case your house is ever struck by lightning, providing a safe alternate path so the strike doesn't blow the entire house's electrical system.


With all the wiring connected (caps tight, no bare wires exposed), you need to push the switch into place. Often, excess wiring will require you to gently bend and bunch the wires to fold up inside the box. Do this gingerly to avoid pulling any wires loose. Push the switch into position.

Step 6

dimmer6Reinsert the mounting screws to attach the dimmer switch to the junction box. Before putting the face plate back on, go back to your circuit breaker and turn your power back on and test your work. If the switch is working just fine, finish attaching the face plate to the wall and you're done! If it doesn't work, make sure power is coming to the dimmer with the electrical tester. If it is, turn off the power and re-check the wiring to make sure you've attached the correct wires together.

Finally, you're ready for a little ambiance. Take that bubble bath, have a date-or show off your dimmer installation skills to your best friend and show her how to do it!

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I just went out and bought a $10 dimmer at Walmart and installed it in about 10 minutes. The hardest part was unscrewing the screws from the faceplate. I will definitely be installing dimmer switches in all of my rooms!

In the article about installing dimmer switches, you said that the color of the wires isn't always the same so use a tester to find out which is the ground wire...what kind of tester, and how do you do that?

I don't think you really would ned a tester. Every time I've replaced a switch, the ground wire is pretty easy to spot: it's almost always green, or, it's an uncoated bare copper one. Also, if you're working with older wiring (say 1960s or before), you may not even have a ground wire. If there are only two wires going into the old switch, you have no ground to deal with. In general, if you're replacing a switch, just follow the scheme of how it was hooked up before--replace everything on the new one the way ot was configured on the old one and it should work fine.

As one of the banking commercial says: Evan a neanderthol man could do it!!!!

OK Please help.... PS I LOVE THIS SITE!!!

I am putting in a dimmer switch for a ceiling fan. Yes I did spend the $$ for a good one, and Its throwing me off...I have out my electrical book, and have visited the ceiling fan company site a few times.. ugh

do we have anything up re: this topic Yet? if not I can give ya'll the details...

Please let me know if I missed the memo LOLOL



What if you are wanting to add a dimmer switch for recessed lights, eight of them, does the watts for the dimmer have to match the total watts of the lights? loloa

YES - the total load must not exceed the rated capacity of the switch. The electronic dimmers you get at the home stores are typically rated at 600watts. If you ONLY put 75 watt bulbs in the recessed lights, AND this is the only dimmer in the junction box, you could get by with a 600watt dimmer. But I'd recommend using a 1000watt rated switch, just to be safe. Otherwise you risk someone else installing 100watt bulbs and overloading the switch. Also, if you have multiple dimmers in a single junction box, the instructions will tell you to reduce the maximum capacity of each dimmer based on the total number of dimmers grouped together. This is because of heat. Dimming a circuit generates heat, and multiple dimmers mean more heat in the junction box. Normally, the expected load is well below the capacity of the switch and this isn't an issue. But with your eight light circuit, you're pushing the max, so you have to take "derating" into consideration.

We've recently moved into a new house. The wall switch that controls the dining room light is a rotary dimmer... but it didn't work. So, thinking it was broken/old I bought a new one and went to install it. No luck. The lutron dimmer I bought isn't even turning the power on - but the old dimmer still does. I did notice that there's no ground wire available. The currently install (broken) dimmer doesn't use on. The lutron dimmer says it isn't needed but I wasn't sure if that might be my problem. Is there some way to test why the new dimmer switch isn't working or why the dimming function of the old switch isn't working? Thanks so much.

I am having trouble installing the switch. My new switch has 3 wires(2 black and 1 green). The old switch has only 2 black wires. How do I know which black wires to connect to the other black wires and where does the green (grounding wire) go?