Three Way Switch Conundrum


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Old 10-26-18, 08:57 AM
J
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Three Way Switch Conundrum

Five years ago, I installed a three-way switch. I ran two three-stranded cables from each switch box, and then in my attic, I connected those in a junction box to a cable carrying power and to one running to the light. For the last five years, the switches have worked properly. Then they stopped working correctly, and I've run a bunch of tests trying to figure out what broke. I've replaced both switches and that didn't help.

The attached picture shows the box in the attic: There are three wires running into the left side and one into the right side. The one on the right side goes to the light. The one on the bottom of the left side is the power. The black strand from the light goes to the black strand from the switch wire that runs to the top left. The black strand from the power runs to the black strand from the other switch (middle left). The white from the light connects to the white from the power. The two travelers connect to their corresponding traveler from the other switch.

Hereís the clearest indication of the problem Iíve discovered: With the power on, I turn one switch on, and the light illuminates. I then flip the other switch, and the light stays on. I then turn off the power and go to the attic. If I take both black wires from the two switches out of their nuts and test them, there is no continuity. This is bizarre. If thereís no continuity, it means the switches are working properly together and should cause the light to turn off. But how is the power still flowing to the light?? If I manually disconnect the black wires and turn the power back on, then the light doesnít work. But the light does work if the black wires are connected (one to the power source and one to the load) even though the black wires themselves donít register continuity.

Another way to explain this is through the grid below. This is how it behaves (if, in the attic, the reds are connected and the whites are connected):

Switch A black and red continuous + Switch B black and white continuous = ON (This is the weird one. It should be off.)
Switch A black and red continuous + Switch B black and red continuous = ON
Switch A black and white continuous + Switch B black and white continuous = ON
Switch A black and white continuous + Switch B black and red continuous = OFF

Any guidance or ideas for further tests I can do to isolate the problem would be greatly appreciated!
 
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Old 10-26-18, 03:05 PM
B
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Hi jeff and welcome to the forum.
I see you are still waiting for some help so I'll just add my thinking to see if it helps. Note, I'm a contractor and not an electrical pro.

I read part of your post but did not try to resolve based upon what i read. Reason is, what is in that junction box should be all you need.

Think about this.
The black and red travelers entering from the two switches get tied together, bk to bk and red to red.
The white from one of the 3-wire pairs goes to the black of the power.
And the white of the other 3-wire goes to the black of the light.
The two whites from the light and power just get tied together.

Looks good on my paper.

Think it through.
Bud
 
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Old 10-26-18, 03:11 PM
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Since you are using red and white as travelers...... they should be on the brass screws of both the switches. One black wire to one switch common should be power and the other black common wire goes to the light.
 
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Old 10-29-18, 04:37 AM
J
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Thanks for your guidance. I ended up taking a short length of three-stranded cable, attaching it to a three-way switch, and connecting it directly to the box in my attic in lieu of the other switch cables. It turns out that one of the cables has a short in it, so I'm going to have to re-run that cable, if I can find a way to push it through the wall down to the switch box.
 
 

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