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How to Install a 3 Way Dimmer Switch

February 7, 2008

This tutorial is on how to install a 3-way dimmer switch. Now I’ve learned that a lot of people call these two way switches, but this is incorrect. They are three way switches. A 3-way switch is used when you want to switch an electrical device (lights, lamps, receptacles, etc…) from 2 or more locations.

Now this circuit is already using 3-way switches, but the homeowner wants to be able to dim their lighting. So I am going to install a Lutron Ariadni AY-603P, 600 watt, preset, incandescent dimmer switch.

The first thing that you need to do is determine what size dimmer switch you need. To do this add up the maximum fixture wattage(s) this switch will control. So let’s say that you have 6 recessed cans all using 65 watt lamps (bulbs) that this switch will control. However, the maximum wattage lamp that you may use in most recessed cans is 75 watts. You need to size your dimmer switch according to the fixture’s maximum wattage rating and not the existing lamp inside of the fixture. So, you need a dimmer switch with a minimum wattage rating of 450 watts (6 x 75 = 450 watts).

There is a label on the fixture that states the maximum wattage lamp allowed for that fixture. If you have a 100 watt lamp in a fixture that is rated for 60 watts maximum, then now is the perfect time to correct this. The extra 40 watts puts off just enough extra heat to make this a fire hazard. This is one of the most common mistakes that I see.

If you want to be able to dim the circuit from either light switch, then you need a master and slave combination similar to a Lutron Maestro. However, in this application the homeowner would prefer the dimmer switch installed in one location. Depending upon your location, this is approximately $50.00 (labor + materials) cheaper than buying and installing the master and slave combination.

Step # 1 – Locate your breaker box and turn off the power to this circuit.

Step # 2 – Remove the switch cover plate. Remove the switch cover plate - Click to enlarge
Step # 3 – Remove the 3-way switch Remove the 3-way switch - Click to enlarge
Step # 4 – Disconnect the wires from the old switch. Note the wire that’s on the common terminal (odd colored screw), as this will need to connect to the common terminal on the new switch. In this installation there are 2 black wires. So, I need to identify the common wire. I usually disconnect this wire last, hold it, grab the new switch and connect it to the common terminal on the new switch first. The placement of the common wire is important. If it is not placed on the common terminal, then the 3-way switching will not work properly. Please see the image to the right. I apolgize for the image quality. It is a little blury, but I believe it still shows what I’m referring to. Note the common terminal - Click to enlarge
Step # 5 – Connect the wires to the 3-way dimmer switch, ensuring the common wire is connected to the common terminal. Grounding is also very important when installing dimmer switches. Ensure you connect the ground wire to your dimmer switch. 3-way dimmer switch right view - Click to enlarge   3-way dimmer switch left view - Click to enlarge
Step # 6 – Install the 3-way dimmer switch Install the 3-way dimmer switch - Click to enlarge
Step # 7 – Install the switch cover plate Install the switch cover plate - Click to enlarge

Step # 8 – Turn on the power and test. When testing 3-way switching, I like to turn on the light from one switch. Go to the other switch and turn off the light. Then go back to the first switch and turn on the light again. If everything works, then you wired it correct. If it does not work, the you probably did not place the common wire on the common terminal.


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18 Responses to “How to Install a 3 Way Dimmer Switch”

  1. Pam Hoffman on February 7th, 2008 10:02 pm

    Hey Wayne!

    It would be very useful to see the schematic drawing for these things – I thought it WAS a two-way switch and I drew what I THOUGHT it would look like for my boyfriend the other day.

    I drew the lamp with the wires coming from it and then the two switches in parallel also connected up with it – really simple. The discussion was about why the light won’t go on if one of the switches is somewhere between totally one way or the other.

    Now, you’ve got me wondering!!

    Pam Hoffman

  2. J.R. on August 3rd, 2008 9:49 am

    Is there a transformer inside the lutron light switch.
    Such as a ballast.
    Do the lutron dimmers constantly use voltage to run this tranformer.?

    need to know because my house is vacant most of the time and i try to shut everything down when iI leave,

    Thanks J.R.

  3. Jerry Sugg on October 7th, 2008 11:18 pm

    Recently installed 3 way dimmer. Replaced each wire as I took off. Now the dimmer works but , if you turn it off you can’t turn it on from the other switch without going back and turning on the switch you first turned off.

  4. Cedric on November 13th, 2008 5:55 pm

    Same problem here – these Lutron Switches came with poor instructions. There is NO marking on the switch to tell you which is the common.
    If you test it with an ohm-meter it does nothing.
    Totally useless. It may be a good product but they maake it crap by providing no proper instructions that work!

  5. Jerry Sugg on November 14th, 2008 2:12 am

    After switching the runners in every position and getting same results, I decided to switch the black wires on the 3-way IT WORKED. You are right about the instruction sheet,it sucks, good luck.


  6. Cedric on November 15th, 2008 7:55 pm

    Thanks Jerry – I finally got it going. I had to get the red and black figured out – these were the two possible paths through the switches.

    Once I realized that the Lutron 3-way had a different colored screw dfor the common terminal it made more sense and I finally got this thing working.

    The result is WELL worth the effort! Just had to trake the time to suss it out!

  7. Eric on March 16th, 2009 10:33 pm

    Regarding a 3-way dimmer on a four-way cicuit, I have a similar issues. My mechanical (standard) switches work perfectly but I can’t get a 3-way dimmer (to replace one of the 3-way switches) to work right. That is, it will not work in all switch positions. According to the vague user information published by the manufacturer (Lutron), it seems you need to use an accessory dimmer with a “Multi-location” 3-way dimmer. This seems completely ridiculous…but it has to be the case. The circuit works perfectly…but not with a dimmer. The dimmer only seems to work with power on the common. When on the runner – no go. Using the same exact wiring with the mechanical 3-way – no problem!
    This is very frustrating…I guess I’ll have to buy an overpriced “assessory dimmer”. Unbelievable!!! What a scam.

  8. JaneRadriges on June 13th, 2009 9:41 am

    The article is usefull for me. I’ll be coming back to your blog.

  9. Jim on June 22nd, 2009 2:18 pm

    Glad I stumbled across this blog. I’ve had the same problem with my Lutron 3-way switch. I can’t wait to keep home to try reversing the wires to see if the common is incorrectly wired. Thanks for the advice. I agree that Lutron’s directions are terrible.

  10. ken snyder on August 2nd, 2009 12:44 pm

    Hi everyone. My problem is I have 6 pendant ceiling fixtures all on the same 3 way switch. Problem is that when I turn on the lights sometimes light 3 doesn’t turn on. I then replace the bulb and light 3 turns on but light 4 doesn’t. I repeat and light 4 now goes on but not light 3 doesn’t. I”ve checked the wiring and it appears right and the work was performed by a licensed electrician several years ago. I don’t remember when this first started but I have ignored it for some time. I am completely baffled and the licensed electrician who installed it has retired and moved away. Any suggestions?


  11. dave remmert on August 15th, 2009 8:14 am

    I have replaced a conventional 3-way switch with a leviton 3-way dimmer switch. The light works properly from both switches (on-off) but the light does not dim from the new dimmer switch. I suspect that the dimmer mechanism in the switch is damaged either from the factory or by me when installing the switch and i need to get another dimmer switch. Is this a correct assumption?

  12. mike crawford on January 1st, 2010 8:35 am

    Can I use extra 3 way dimmer switches in place of 1 way dimmers which I do not have?

  13. James Miller on January 1st, 2010 2:44 pm

    Light come on but getting no power to light switches.

  14. jim williams on May 17th, 2010 7:24 pm

    I have just installed a new 3-way circuit in my unfinished basement. When I use conventional 3-way switches, everything works perfectly, but when I replace one of the switches with a 3-way dimmer switch, the lights do not dim. Do I need to wire this differently when I place one dimmer in the circuit. Or, is it possible that I have a defective dimmer switch. If so, is there an easy way to test a 3-way dimmer switch to see if it is defective. Thanks in advance for any help you can provide.

  15. Thomas Jesberger on August 19th, 2010 6:23 pm

    can I use two three way dimmer switches to control a light from both locations

  16. MATTHEW THORNE on March 14th, 2011 4:06 am


  17. Paul on May 12th, 2011 1:11 pm

    Here’s a Q. I have 2 three way switches that power my dining room chandelier. A toggle and a dimmer. The toggle needs to be in the “on” position for the dimmer switch to work. Any clue what the issue is? I opened the box covers and there are two black wires, a white wire and a bare ground. (The house is only 20 years old and has no red wires?). I replaced both switches and neither was the cause. I tried swapping the black wires and still no result other than funky combinations of off is on and on is off etc… The toggle operates as a single pole switch and I have no idea why. Please give me some thoughts as to how to correct this.

  18. Lou on December 16th, 2011 6:05 am

    If you have multiple switches at both sites of a 3 way switch with many common wires, is it still possible to install a dimmer switch on the 3 way light?
    I have tried but either the dimmer doesn’t work or one of the switches will not turn the lights on or both.
    Any solution or will dimmer not work?