3-way switch question

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  #1  
Old 08-08-14, 03:57 PM
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3-way switch question

I tried replacing a 3-way switch that seems to be faulty. The light does not always come on, but you can pound on the wall near the switch and then it will usually work.

Looking at the new switch, it is a mirror image of the old one--two screws on the left and "common" on the lower right, rather than two screws on the right and "common" on the lower left. So I attached the wires to look the same except on opposite sides. But the bulb did not light when switched. So I reinstalled the old one for now. I assume the new one is not really the problem.

I am wondering if maybe because of the way the circuit is wired, or the nature of the switch, I cannot just follow the same connection pattern.

I do not know if this circuit is panel-switch-switch-light or panel-switch-light-switch. Or if that would matter.

I am not sure how to proceed.

All help greatly appreciated.

Gary
 
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  #2  
Old 08-08-14, 04:03 PM
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It's panel switch switch light. Do you have a multimeter to determine the hot wire coming from the terminal?
 
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Old 08-08-14, 04:26 PM
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Ensure the hot and load wires are connected to the black or anodized screws of the switches. Usually a black wire, but you should make sure. The other two, usually red and white connect to the other screws, but in no particular order. Not all switches are the same, so mirroring may not work.
 

Last edited by pcboss; 08-08-14 at 04:48 PM.
  #4  
Old 08-08-14, 04:28 PM
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The wire that came off the dark color screw on the old switch MUST go to the dark color screw on the new switch. Order or side is of no concern.
 
  #5  
Old 08-08-14, 05:16 PM
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Looking at this switch, I have common on the upper left; in the "off" position, this terminal reads 15, the upper right white wire reads 120 and the lower right black wire reads 0. In the "on" position, the common reads 15, upper right white wire reads 120, and lower right black wire reads 120.
 
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Old 08-08-14, 05:28 PM
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I'm not quite sure what you are trying to measure but you should have one traveler that stays hot in either position. You should have another traveler that stays at 0v. The common should read 0v in one position and 120v in the other position.
 
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Old 08-08-14, 05:32 PM
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I have common on the upper left
A 3-way switch has not top or bottom or left or right. Only the common wire is important. At one switch power in goes to the common at the other switch power out goes to the common.
in the "off" position
Thre is no "off position on a 3-way switch.
the common reads 15, upper right white wire reads 120, and lower right black wire reads 120.
Voltage readings aren't that meaningful but the common should read 120 volts to ground if is the common power in is connected to.
 
  #8  
Old 08-08-14, 05:45 PM
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OK. I can see that I am all wet here.

Looking at it again, the lower right screw is darkened and says "common." This reads 0 when the light is not on and reads 120 when the light is on.

The upper left screw is silver and reads 15 when the light is on and 15 when the light is off.

The upper right screw is silver and reads 120 when the light is off and 120 when the light is on.

This is a staircase switch. It has worked consistently until recently. Now when you flip it on, the light might turn on, or it might just flash and then turn off, or never turn on. If you flip it to "on" and the bulb does not light, or just flashes then turns off, you can try again and again, or sometimes pound near the switch, and the light will usually come on.
 
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Old 08-08-14, 06:01 PM
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Remove the switches and lay them on a table. Separate the wires from the switch, red, white, black and ground. Test the wires to ground for voltage. Black should be 120v on one switch and 0 on the other one. The one with 120v will be LINE. Connect that black to the anodized screw and the other wires to the other screws, ground to green screw. Do the same at the other switch, black to anodized screw, etc. Test to see if the light works. You'll go crazy with phantom voltage and a digital meter.
 
  #10  
Old 08-08-14, 06:35 PM
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OK. Let me try again. I have been mis-describing the problem.

With the old switch, you could turn the light on from upstairs or downstairs. With a new switch, you lose this feature. You cannot turn on the light from either end. One switch has to be in a particular position. The new switch looks like the old (3 contacts, one says "common" and has a dark screw, and there is no ground). But it doesn't work like the old.

The shorting problem seems to have disappeared, but now you cannot turn the light on from either switch. If the downstairs switch is in one position, the upstairs switch will not turn on the light.
 
  #11  
Old 08-08-14, 06:49 PM
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What color wire do you have connected to the "common" screw of each switch?
 
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Old 08-08-14, 06:52 PM
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Silver screw? You should have two brass and a dark gray.
 
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Old 08-08-14, 06:56 PM
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Downstairs, the wire connected to the "common" screw is red. Upstairs, it is black. The only red wire in the upstairs box is wirenutted at the back of the box. It doesn't terminate in that box.

Yes, I guess the other screws are brass colored. And, I guess the new switch that I bought does have a green screw; the old one does not.
 
  #14  
Old 08-08-14, 07:01 PM
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does the new switch say off and on on the handle.
 
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Old 08-08-14, 07:02 PM
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The only red wire in the upstairs box is wirenutted at the back of the box.
Wire nutted to what? What color wire on the common in the upstairs box? Does one of the boxes have a 2-conductor cable (black and white)?
 
  #16  
Old 08-08-14, 07:15 PM
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The new switch doesn't say "off" or "on."

In the upstairs box you can see a red wire coming out of a 3-wire black sheath; it is wirenutted to 2 blacks and then goes back down the wall. The black and white from that 3-wire were connected to the brass terminals of my switch.

The wire that was connected to the "common" screw comes from another Romex in the box, a black wire coming out of a 2-wire cable.
 
  #17  
Old 08-08-14, 07:19 PM
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did you change the downstairs switch
 
  #18  
Old 08-08-14, 07:20 PM
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I haven't done anything to the downstairs switch.
 
  #19  
Old 08-08-14, 07:27 PM
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did you change the upstairs switch.
did you take the wirenut apart in the upstairs switch.
 
  #20  
Old 08-08-14, 08:04 PM
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if you did not open up any wire nuts ........the wiring sounds correct.

the downstairs switch could be bad....install the new switch downstairs keeping the red wire on the common screw.

does the downstairs switch box have one cable only with the red to the common and the black and white to the 2 brass screws.
 
  #21  
Old 08-08-14, 09:00 PM
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I'm trying to figure out your description of the switch at the top. How can this diagram be changed to be correct. (Cable sheath colors are only for identification and may not match yours.)

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  #22  
Old 08-09-14, 09:22 AM
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The upstairs box is crowded, (three 2-wire cables, one 3-wire cable, two wire nuts joining multiple wires from these cables, and multiple ground wires neither attached to anything nor bound together).

ray2047's diagram would be changed this way: the black and white from the 3-wire cable go to the brass screws. The black from the 2-wire cable goes to the dark screw (marked "common").

The white from the 2-wire goes to a wire nut. So does the red. There are 2 big wirenuts; I'm not sure if these go to the same wirenut or different ones.

The only thing in the downstairs box is a 3-wire cable with an unused ground. The red goes to the dark screw on that switch and the white and black go to the brass screws.

For johnsc: yes, the downstairs box has only the 3-wire cable, attached as you described.

I have not opened any of the wirenuts or done anything else. I have only tried to replace the upstairs switch with one that appeared identical and when I did this I could no longer turn on the light from either switch regardless of the position of the other switch.
 
  #23  
Old 08-09-14, 10:11 AM
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and multiple ground wires neither attached to anything nor bound together).
For now forget the ground wires. They are not relevant to this discussion.
ray2047's diagram would be changed this way: the black and white from the 3-wire cable go to the brass screws.
That is their location on the diagram. I will label the screws to make it clearer.
The white from the 2-wire goes to a wire nut. So does the red. There are 2 big wirenuts; I'm not sure if these go to the same wirenut or different ones.
I need to know the color of all the wires in the wire nuts.
 
  #24  
Old 08-09-14, 10:23 AM
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After you reexamine the upstairs box is this what you see.

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  #25  
Old 08-09-14, 10:24 AM
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One wirenut holds the red and 2 blacks. The other wirenut holds 3 whites.

I tried replacing the lower switch and got the same result. The light will not go on from either switch.
 
  #26  
Old 08-09-14, 10:33 AM
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The switch in your diagrams is different from mine. Mine has the two brass screws across from each other, rather than on the same side. So I am not sure which is the traveler on mine. But otherwise this is correct--the black and white from the 3-conductor go to the brass screws and the black from a 2-conductor goes to the "common;" the white from that 2-conductor wire goes into the wirenut containing 3 white conductors.

I don't know if this matters, but the screws on my replacement switch are silver rather than brass.
 
  #27  
Old 08-09-14, 10:47 AM
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Common always goes to the odd colored screw switch regardless of position.
but the screws on my replacement switch are silver rather than brass.
That is unusual. I would wonder if it was a 3-way switch.
the white from that 2-conductor wire goes into the wirenut containing 3 white conductors.
Looking at my diagram where does the third white come from?

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Is this the wiring for the downstairs switch?

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  #28  
Old 08-09-14, 12:05 PM
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Common always goes to the odd colored screw switch regardless of position.
I have assumed the red in the downstairs box, connected to common, is the same red appearing in the upstairs box; but that red does not connect to the common on the upstairs switch; it is wirenutted to the other black wires coming into that box.

That is unusual. I would wonder if it was a 3-way switch.
If true, that could be a complete answer, I would think. If the old switch really is bad but I don't have the right replacement. I will attach photos.

Looking at my diagram where does the third white come from?
This circuit serves other ceiling lights around the house. There are 4 white conductors coming into the upstairs box. Three come from three 2-conductor cables coming into the box and one comes from the 3-conductor cable. All the whites from the 2-conductor cables go into a wirenut. The white and black from the 3-conductor cable go to the upstairs switch; the red connects with the remaining black conductors in a wirenut.

Looking at your diagrams, I see your switch is different from my existing switches and my replacement switches. Your diagram has the brass screws on one side and the dark screw on the other. On mine, the "brass" screws are across from each other; this is true of my replacement switch and both existing switches.

Is this the wiring for the downstairs switch?
The downstairs switch has the "common" at one end and the two brass screws at the other end, across from each other. The box contains a single 3-conductor wire. The red is on the "common" and the black is on the brass screw located on the same side as the red. The white is on the other brass screw, which is located on the opposite side of the switch, across from the brass screw containing the black.
 
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  #29  
Old 08-09-14, 12:56 PM
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Please stop concerning yourself with the position of the screws on the switch. That doesn't matter. What matters is the common wherever it is. The screws look brass to me.

I don't believe Larry's diagram represents what you have. The screws on your new switch look brass to me. Try replacing the upstairs switch with a new one also. Your connections do look correct in bot boxes. Revised diagram:

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  #30  
Old 08-09-14, 01:22 PM
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The revised diagram does look correct to me.

When I replace both with new switches, I get the same result: you cannot just turn on the light from either switch. I have not tried moving the black and white wires to the other brass screw on either switch.
 
  #31  
Old 08-09-14, 04:14 PM
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Well, I bought a new 3-way switch and installed it upstairs, and everything seems to be working ok. Thank you for all the terrific guidance.

I put an ohmmeter on the two other "new" ones I was using. They don't work the same. When you connect common with one of the brass screws and flip the switch, the ohms moves from 1 to 0; connect common with the other brass screw and it does the same. On the second "new" switch, when you connect common with one of the brass screws and flip the switch, the ohms moves from 1 to 0; connect common with the other brass screw and flip the switch and it stays on 1.

Would you agree this is probably what was happening? Bad replacement switch?
 
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Old 08-09-14, 04:30 PM
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Your test results confuse me a bit. but the good thing is it works.
 
  #33  
Old 08-09-14, 04:34 PM
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Many, many thanks! This is very helpful. Gary
 
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