How to wire a dimmer on a 3-way switch?
December 21, 2014 4:09 PM   Subscribe

Need help wiring a dimmer on a 3-way switch circuit.

I have a 3-way switch circuit in my house with 8 65w BR-30 fixtures attached. I have LED lights installed in the fixtures. The switches are Lutron regular rocker switches, nothing fancy. I want to install a dimmer. I bought a Maestro C-L Lutron switch.

When I install the dimmer, the 3-way switch does not work properly. I can't turn the light on and off independently from both switches. The non-dimmer switch needs to be in an "on" position to turn the lights on with the dimmer switch. If the non-dimmer is in "off" position, the dimmer can't turn the lights on. If the non-dimmer is in the "on" position, I can turn the lights on and off with the dimmer.

What is really confounding is that the 3-way switch works fine when I have the simple Lutron rocker switches installed on both ends. That is - both switches can turn the lights on and off independently. It's only when I switch one out for the dimmer switch that I have the issue where the switches no longer work independently.

I am 99% sure I have the "common" correctly identified, because the simple switches work fine when I hook them up. When I use exactly the same wiring (the same "common") with the dimmer, the switch no longer works independently.

I bought two of the dimmer switches and have tried them both - same results (i.e., it isn't the switch).

Any ideas? Thanks.
posted by Mid to Technology (13 answers total) 1 user marked this as a favorite
Did you complete all of the installation steps? In the instructions for the Maestro CL, there's a Step 9, titled "Additional Setup" that requires an additional step for 3 way switches. Step 9 will point you to additional instructions on the other side of the page.

I just installed this same dimmer a few weeks ago on a 3-way switch and completely missed Step 9 the first time around.
posted by jal0021 at 4:33 PM on December 21, 2014

Response by poster: No, did not see that at all - trying now.
posted by Mid at 4:37 PM on December 21, 2014

Response by poster: Sadly, that does not do it. When the non-dimmer switch is off, it's like there is no power going to the dimmer switch at all - the little green light is off.
posted by Mid at 5:07 PM on December 21, 2014

Response by poster: If it matters, when I use my voltage detector, with the non-dimmer off I get voltage in two wires (one red one which I am pretty sure is the common and one blue one which I think is a runner) but no voltage in a 3rd wire (another blue one). When I turn the non-dimmer on, there is voltage in all 3 wires.
posted by Mid at 5:11 PM on December 21, 2014

Perhaps a stupid question, but are your LED bulbs "dimmable?" To the right of the switch, the web page lists the LED "Load Types" as "Dimmable Light Emitting Diodes (LED)." Perhaps you have non-dimmable LED bulbs?
posted by InsertNiftyNameHere at 6:04 PM on December 21, 2014

I'm 99% sure your LED bulbs aren't dimable, or are called such but aren't really. I've run into all qualities of dimmability in CFL and LED bulbs.

The give-away, IMO is that the 3-way works fine with two rocker switches.

Also, you really want to be careful about that 1% when working with electricity.
posted by humboldt32 at 7:19 PM on December 21, 2014

Do your bulbs dim when the non-dimmer switch is on? That's an easy check to make sure everything is OK with the bulbs.

From your description, I have some suspicion that your non-dimmer switch is miswired. Did you check that? Is your common wire definitely on the common terminal in that switch? The two travelers are on the traveler terminals? Nothing weird like a traveler wired to the ground terminal?

If you've double (and triple) checked the wiring on both of your switches, the next thing I'd check is to make sure that your wiring isn't miscoded. For example, I hope that one of your blue wires isn't a common wire.
posted by Betelgeuse at 8:31 PM on December 21, 2014

Did you turn off the breaker? Or just turn off the switch?
A three way switch has one leg that is always hot - and it is easy to burn up a new dimmer at installation.
posted by Flood at 4:15 AM on December 22, 2014

Best answer: I'm surprised no one has asked this yet. Is your dimmer a 3 way dimmer? you can't put a normal dimmer switch in a 3way configuration. The specification document from Lutron says specifically that in a configuration where you have one dimmer amongst 3 way switches, you need a 3way dimmer. According to the spec for the model you bought (the maestro CL), it is "multi-location", which following the guide means that it works as a 3way type switch only in conjunction with other multi-location "companion" dimmers, but not with other normal or 3way switches.
posted by postergeist at 5:56 AM on December 22, 2014

Response by poster: Thanks everyone. I think postergeist may have it or be the closest.

1. The problem does not seem to be related to dimming the bulbs (or a particular type of bulb) because, when I can get the dimmer working, the bulbs dim fine. This happens when the non-dimmer switch is on. The problem is that when the non-dimmer switch is off, there is no way to turn the lights on from the dimmer switch. In other words, the product works fine so long as I don't mind walking across the room to turn the lights on and off at switch #1 (the rocker) and them dimming the lights at switch #2 (the dimmer). In fact, if I leave switch #1 on all the time, I could use switch #2 to do everything.

2. I am pretty sure I have the common wire figured out, because when I wire up the old rocker switches, they work fine and independently. I don't pretend to understand 3-way wiring, but I don't think the rockers would work correctly if my common was wired into one of the runner posts. (?)

3. I'm pretty annoyed that they make this switch for 3-way applications but fail to give it whatever 2-cent feature it needs to act like a dumb rocker switch made by the same company.
posted by Mid at 6:45 AM on December 22, 2014

A simple check to see if your dimmer is set up for a three way switch: are there four terminals (common, two travelers, ground) or three terminals (common, load, ground)? If the former, it's a three way switch. If the latter, it's not.
posted by Betelgeuse at 9:26 AM on December 22, 2014

Response by poster: That's what's so confusing - the dimmer has four terminals, just as you say, but it seems like the switch is not designed to work with a regular 3-way switch at the other end. Instead, you need something called a "companion dimmer" at the other end.
posted by Mid at 2:49 PM on December 22, 2014

Response by poster: Postergeist had it - I finally got around to installing the "companion" switch and it all works fine. So strange they don't just say on the box "This won't work as a 3-way unless you buy the companion switch."
posted by Mid at 12:37 PM on February 22, 2015

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