3 way switch wiring


Old 05-27-06, 12:04 PM
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Join Date: Dec 2005
Location: USA
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3 way switch wiring

What started as a simple project has me a little confused. I was installing a new outlet in a long hallway. The hall has two, 3 way switches controlling a ceiling light. My plan was to tap into the light circuit at a switch and install the outlet in the same bay as one of the switches.

I got a little confused when I pulled the switches. One has just one cable a 14-3 connected as expected. The other switch has a 14-3 cable and a 14-2 (coming from the light). The hot wire is a white (marked black) from the 14-2 cable connected to the common. The travelers are the 14-3 red and white wires. The black wires from both cables are tied together.

I'm sure this is a switch loop with the light at the beginning of the run, but I don't know why the W/B wire is used as the hot instead of the black. I suspect the 14-2 wires are backwards but of no consequence since the circuit is correct. If I was wiring this I probably would have used the 14-2 black as the hot feeding the first switch and returned the 14-2 white (marked as hot) to the light.

Never having run into this before, I thought I would take a coffee break and ask for guidance.
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Old 05-27-06, 05:06 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Without looking at the light or taking measurements (with a meter or a circuit tester) , you don't know which wire of the 14-2 is always hot and which is switched hot. The white wire should be always hot (remarked as black.

Anyway, you cannot tap this for a receptacle, just as you cannot tap any switch loop for a receptacle. It you want to be able to get a receptacle here, replace the 14-2 from the light to the switch with a 14-3 and then you can add in a receptacle.
Old 05-28-06, 09:36 PM
Join Date: Mar 2006
Location: Fort Collins, Colorado
Posts: 159
I agree with Bob. There is no neutral at either switch. If you were to take the light down, you'd (hopefully) discover that there is full-time power at the box for the light fixture. The neutral is way up there.

The power travels down the white wire to the common of the 1st switch,
goes through the travellers,
comes out the common of the far switch (the one with only the three-wire in the box),
returns to the first switchbox (on the black wire with the travellers),
and then is tied to the black wire running to the light fixture.

With no neutral at either switch, there's no way to power a receptacle from either.
Old 05-29-06, 06:18 AM
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Join Date: Dec 2005
Location: USA
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I knew that I couldn't tap the switch loop for power. I ended up going to the ceiling box for the light. My confusion was from the way the switch loop was wired. I didn't expect the cable from the light to use a W/B as the hot when the black wire was available.
After thinking about it a bit, IMO the wires in the 14-2 cable leading to the first 3 way switch in the loop were reversed from how I would have connected them but it made no difference since the hot white wire was correctly identified with black paint.
Old 05-29-06, 08:19 AM
Join Date: Nov 2005
Posts: 249
My guess is that instead of running the 3 wire cable to the light the light terminals were brought down to the switch. I did this where I had five rooms coming into a den and needed to expand the single switch circuit that was there. If this is correct both wires to the light should be black and the existing wiring is correct.
Old 05-29-06, 09:17 AM
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Join Date: Dec 2005
Location: USA
Posts: 3,188
That's how it's wired. Once I opened up the ceiling box it I figured it out. The light is over a stairwell and I was too lazy to break out the ladder.

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