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How to Install a Dimmer Switch

February 22, 2007

This is a simple project that most homeowners can tackle themselves and complete in less than 30 minutes.

The first thing you need to do is determine which size and type of dimmer switch you need to install.

Sizing your dimmer switch is very easy. Dimmer switches are rated according to the lighting load they will dim. Let’s say you want to dim your dining room chandelier. This chandelier has 8 – 100 watt light bulbs in it. This means that the total lighting load you want to dim is 800 watts. You can reduce this load by changing the light bulbs to 60 watts each. This would give you a total lighting load of 480 watts.

The smallest dimmer switch you can get is 600 watts. From here the next size is 1000 watts, 1500 watts, 2000 watts, etc… The 600 watt and 1000 watt dimmers are the most common. Anything above 1000 watts will no longer fit into your standard single gang switch box. These larger switches typically require their own 2-gang switch box.

Now let’s talk about type; I would like to discourage you from getting those cheap rotary style dimmers. These control the light level through a variable resistor. Less resistance increases the light level and more resistance decreases the light level.

The problem with this solution is that you end up using a lot of energy to heat the resistor, which doesn’t help you light up the room but still costs you. In addition to be being inefficient, these switches tend to be cumbersome and potentially dangerous, since the variable resistor releases a substantial amount of heat.

The newer style resistors rapidly turn the light circuit off and on to reduce the total amount of energy flowing through the circuit. This results in better efficiency and less energy loss through heat. To learn more about this style, I recommend reading “How Dimmer Switches Work“.

You also need to determine if you need a single pole or 3-way dimmer switch. A single pole switch will only turn on or off the light from 1 switch. A 3-way switch will turn on or off the light from 2 or more switches.

With 3-way switches you only need to replace 1 of the 3-way switches with a dimmer. If you want to dim your light from multiple switches in a 3-way circuit, you will need a master and slave(s) combination. The Lutron Maestro series is one I recommend here.

To replace your switch, you first need to turn off the power supplying this circuit. Now go remove the cover plate and use a voltage tester to ensure that the power is indeed off. Never assume the power is off. I have seen some very scary stuff over the years, resulting in me getting shocked by assuming the power is off. Never assume the power is off and always test before touching any wires or devices.

Loosen the screws on your old switch and pull it out of the box. Now, before you disconnect the wires, make a note of how they are connected to your existing switch. This is very important to make your 3-way switches work porperly. I recommend writing this information down or taking a picture with a digital camera.

When reconnecting your dimmer switch, it is very important to ensure the ground wire is connected to the new dimmer. If the dimmer switch has screw terminals to connect your wires to, be sure you wrap the wires clockwise around the screw terminals. This will allow the loop in the wire to close with the final turn of the screw resulting in a better electrical connection.

If you have questions or need further clarification on this matter, please submit your questions in the comment section of this post.

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11 Responses to “How to Install a Dimmer Switch”

  1. Paul Reilly on March 5th, 2007 9:57 pm

    I am trying to install a dimmer switch in a three switch panel. One switch is paired to an upstairs switch as well, but seems to be a separate circuit because it stays live when the power is off to the other two. I used a single pole 600 w.slide dimmer, but nothing happens when turned on. I just want to control the one circuit,four ceiling lights 60 w each, but do I need a 3 pole switch because I’m hooking into a three switch panel? The house wires are red, black and white, I’ve connected the switch wires (2 black,one green) as follows, black to red, black to black, and green to white. seems to be what the instructions suggest. (why can’t the industry make colours match?!)I’ve also tried grounding the green on the adjacent switch. Nothing happens. Whats wrong?

  2. Administrator on March 6th, 2007 6:30 am

    Hey Paul,

    Thank you for your electrical question.

    It sounds like you are trying to use a single pole switch where you need a 3-way.

    Were all three wires connected to the old switch?
    Are these 4 ceiling lights switched from another location?

    If you answered yes to these questions, you need a 3-way switch.

    To install your 3-way switch, connect the green to ground. The black is probably the common and this will connect to the odd colored screw or wire. The red and white are probably your travelers and these connect to the other 2 screws or wires.

    Be sure to turn off both circuits before changing your switch and verify that the power is off using a voltage tester.  

  3. richard lesnew on March 6th, 2007 3:38 pm

    I am in a large office building with many private offices. Each office has 4 to 6 2′ X 4″ florescent fixtures with the new energy saving bulbs. We have a gentlemen in our company that shuts your office lights off every time you leave the building, even if it’s only going to be for half an hour. It was my understanding that it takes more energy to start a ballast then to leave it on. Is this correct and it so is there a general amount of time where it does become important to shut the lights off.


  4. Administrator on March 7th, 2007 3:39 am

    Hey Richard,

    Thank you for your electrical question.

    The general rule-of-thumb for when to turn off a fluorescent light is if you leave a room for more than 15 minutes.

    Click here for a good article that explains this well on the U.S. Department of Energy’s website.

  5. Cleiver Varillas on April 15th, 2007 4:11 pm

    I want to install 4 lights (50 watts each) with two 3 ways Dimmer swtches, one in each end of the room, how should I do it?

  6. Administrator on April 15th, 2007 7:40 pm

    Hello Cleiver,

    Thank you for your electrical question.

    One of the easiest way to wire for 3-way switching is to supply power to one switch box with a 2 conductor cable with a ground. Then install a 3 conductor cable with a ground between the 2 switch boxes. Next run a 2 conductor cable with a ground from the opposite switch box that you supplied power to and connect it to the closest light. Now just run a 2 consuctor cable with a ground from light to light. Be sure to match the existing cable size (eg. 14/2 or 12/2) if you tap power from the closest power source.

    I have some 3-way switch wiring diagrams that may help you located at:

    As for the 3-way dimmer switches. If you want to dim this light from both switch locations, then you need a master and slave combination of switches. I recommend the Lutron Maestro dimmers.

    If you do not wish to dim the lights from both switch locations, then you may install a regular 3-way switch in one end and a 3-way dimmer in the other end. This is a little cheaper to do.

  7. jared on June 5th, 2007 3:22 pm

    i want to install under cabinet lighting and i want to use an existing outlet, turning the outlet into the dimmer switch for the lights. this outlet is wired to another outlet and these 2 are on a seperate breaker, is this ok??
    many thanks….

  8. Ty Stinson on June 28th, 2007 11:34 am

    I purchased a 16-light chandelier and started getting it ready to hang. I noticed that in the hub, where all the individual black and white wires are, someone had had started to bundle black wires to white.

    I thought that all white should be joined using pigtails and that all black should be treated in the same way so that all white hook up to one of the leads and all of the black hook up to the other lead in the two wire cord.

    Is this correct?

    Thank you.

  9. steve on August 26th, 2007 1:04 pm

    i replaced light switch with dimmer,and outside the box it works fine.A soon as i tuck the wires into box,and put cap on, i flick the breaker back on and the breaker above it sparkes,and lights doesn’t work.Is there a proper way of putting wires in electrical box?

  10. steve on July 12th, 2009 5:51 pm

    I recently replaced my kitchen cabinets and i am no longer able to use the light switch due to the cabinets covering the switch. It was on a 3 way outlet (2 switches could control the light) but now I only use 1. I would like to install a dimmer switch. Can I use a single pole dimmer and cap off the traveler wire? Any help and diagram would help!! Thanks!

  11. Edwin on April 15th, 2010 6:57 am

    I had a power surge the other day in my house that fried all of my dimmers. As I’ve begun replacing them I noticed that the old dimmers were not grounded to the green wire. Shouldn’t my electrician that initially installed the dimmers have grounded the dimmers? I noticed that the dimmer ground wire was simply cut off. If these dimmers were grounded, would this have prevented the power surge from ruining the dimmers.