View Full Version : 3 Way Switch power fails at Light

07-09-2008, 09:05 PM
Gentlemen...I've installed a new light. Poorly. The chain looks like this:

Power source (14/2) -> 3 way dimmer -> 14/3 romex to standard 3 way switch -> 14/2 romex out to light fixture.

The electricity runs through the chain fine until I screw in the light, which disrupts the power. I've checked the connection at the power source, the dimmer, and the 3 way switch. Somewhere, I've completely botched something on either the dimmer or the switch or both. Followed the directions to a T, but can't get it to jive. Power even comes through the light receptacle, until I screw in the bulb.

Here's the "schematics" I used. http://www.homeimprovementweb.com/information/how-to/three-way-switch-option1.htm.

I'm completely stumped. What did I do wrong? Holler if a diagram will help out. I can get nasty with photos of my "craftmanship".


07-10-2008, 06:03 AM
Not sure if this helps, but some electronic dimmers will show voltage with a high-impedance DMM, but no current. WHen you throw in the lamp, the voltage drops. This is normal until you trigger the dimmer circuit to pass current. Also, many electronic dimmers won't work unless the actual load is greater than (in the order of 25W). Make sure the bulb is big enough (a CFL won't work with many dimmers, even if it is rated as being dimmable).

07-10-2008, 06:07 AM
The wiring diagram you are using is for two regular 3-way switches.

Might want to replace the dimmer with a regular 3-way switch as a test just to check your wiring.

Then to get the dimmer to work, *very* important to follow the directions and wiring diagram which came with the 3-way dimmer. Does it say you can use the dimmer with a regular 3-way switch? Or do you need a "special" switch at the other end?

I assume you have turned the dial on the dimmer back and forth and are using a regular light bulb? I seem to recall reading something about compact fluorescents and dimmers having problems???? Anyway might want to try a regular light bulb for testing.

07-10-2008, 07:23 AM
IF you have described the wiring entirely, then where is the neutral to the light? If the power comes to the switch and then to the light you need 4 wires, not three. And do not use the bare ground for the neutral the way I have seen some handymen do it.

07-10-2008, 08:03 AM
Thanks for the help so far...maybe a little more explanation will help.

I re-checked this AM before heading to work, and I'm 90% certain I've got the dimmer and 3way switch wired correctly. When I check the volts with a 120v tester, it works fine when i toggle either the dimmer or switch. Both switches behave appropriately.

When I screw the bulb in, the power at the 3 way switch starts acting funky. The wires that were previously hot no longer are. It's as if when I make that connection with the bulb to the wires, the power gets reversed/inverted/i don't what.

The lights are recessed lights. 4 in total. We've got them installed on other dimmers in the house that work fine. The bulbs look like this.


Could something in my daisy chain of additional lights be causing the issue?

07-10-2008, 08:10 AM
IF you have described the wiring entirely, then where is the neutral to the light? If the power comes to the switch and then to the light you need 4 wires, not three. And do not use the bare ground for the neutral the way I have seen some handymen do it.

for my neutrals -

Power source 14-2 neutral passes to 14-3 neutral at first location (dimmer). At 3 way switch location, the 14/3 neutral then passes to the 14/2 neutral, which runs up to the lights. Make sense?

07-10-2008, 12:16 PM
It sounds like you have a back circuit and as long as the hot and neutral are separated you indicate proper voltage, but once you insert the bulbs, which complete a circuit that makes the hot wires neutrals because the actual "hot" source is elsewhere. The dimmer circuity could do it if the switch does not activate the hot wire to the lighting. In which case you would have 120v across the switch terminals when the light should be on.

07-10-2008, 01:45 PM
Are you certain you've wired the switches properly? Different 3-way switches might not have their traveller and common terminals in identical locations, and I imagine the dimmer could be different as well. The common terminal is the most important of the 3, and must be wired as shown in your diagram. The other two terminals can be wired in either of the 2 possible ways and things will work.

07-10-2008, 01:48 PM
thanks guys. I've got a few more ideas now to test and test some more, so if i can't figure it out i'll bring in the pros!

07-10-2008, 05:37 PM
Just a general comment....some of your measurements are possibly across an open, and putting a bulb in changes the circuit.

07-10-2008, 06:05 PM
Thanks again, especially for the comment from Billy Bob. I changed out the dimmer with a standard 3 way and the lights functioned perfectly. Problem isolated - bad dimmer - most likely from me frying it from having it poorly wired initially. Replaced with a new dimmer and it worked again.

Problem solved!