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Old 03-03-2011, 11:17 AM   #1
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Adding a light to a three way switch


I would like to add a light to our stairway to the basement. It is a U shaped staircase with the only lights at the bottom, so the centre part is very dark. The lights are controlled with a three way switch at the top and one at the bottom. Here is a diagram of the wiring.

What I had in mind, was to add a sconce to the wall, and I have open access behind the stairs to do the wiring. I want to add the light by adding a 14 x2 wire and pigtailing into the hot that goes to the downstairs switch and then the neutral with the other two neutrals. I did a test with a fixture that I have and it worked with the two switches. The second diagram shows what I plan to do. I was just wondering if anyone knows of any reason that I should not do it this way.

Oh yes, I am from Canada, if that helps.
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Last edited by lovetobuild; 03-03-2011 at 11:25 AM. Reason: add information
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Old 03-03-2011, 11:51 AM   #2
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Adding a light to a three way switch


If you tie the second light hot to the (switched) hot from the switch common screw to the first light, then you are okay. The lower left picture is fundamentally correct.

If you tie the second light hot to the (raw; source) hot going back to the panel (may look the same) or tie anything to one of the travelers then it will not work.

You cannot hook the second light to a 3 way switch that has only three wires coming in and all attached to the switch (center right picture).

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Old 03-03-2011, 12:37 PM   #3
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Adding a light to a three way switch


Hi Allen. I was just working on my diagrams again. The diagram I show with the new connection is not exactly as I did it in the test.

The original wiring to the basement switch (the one in the top diagram) has the hot source going into the back of the common spot on the switch. They inserted the wire directly, not using the screw head.

In my test....I attached the hot wire for the light to the common screw head...and then the neutral piggy-tailed with the other neutrals.

That way, the switch works for the new light. If I piggy-tailed the new hot the way I have it in the boxed diagram...I realize that the switch would not affect the current for the new light.

So....Can I wire it to the common screw head even though there is a wire coming into the back of that common spot...in essence, having two wires connected to the common screw? Or would that over heat the switch?
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Old 03-03-2011, 12:46 PM   #4
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Adding a light to a three way switch


As long as your box is at least 344ml (21 cubic inch) you will be fine. Otherwise the box is over filled and needs to be changed to a larger one.
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Old 03-03-2011, 01:17 PM   #5
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Adding a light to a three way switch


Thanks Allen and Joed:

The good news is, it is a 3 gang box and there is lots of room. Thank you for your help.
It certainly made it easier since the original wiring was direct to the back of the switch, otherwise I don't know how I could connect after the switch.
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Old 03-03-2011, 04:56 PM   #6
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Adding a light to a three way switch


I think that if possible it would be much easier to go from one of the lights to the new light
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Old 03-03-2011, 06:31 PM   #7
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Adding a light to a three way switch


Quote:
Originally Posted by lovetobuild View Post
So....Can I wire it to the common screw head even though there is a wire coming into the back of that common spot...in essence, having two wires connected to the common screw? Or would that over heat the switch?
Yes. Two wires connected to that spot will not overheat the switch.

But two wires may not be held under the same screw head unless there are ridges or a small cover plate that hold the wires in place without curving them around the screw and the wires can't slip out sideways before you tighten the screw fully

The preferred way to connect two wires to the same spot with one screw is to cut a short length of wire of the same color and put just that wire under the screw. Then wire nut the other end to the other two wires.
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Last edited by AllanJ; 03-03-2011 at 08:24 PM.
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Old 03-03-2011, 07:42 PM   #8
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Adding a light to a three way switch


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Originally Posted by Saturday Cowboy View Post
I think that if possible it would be much easier to go from one of the lights to the new light
I wanted to avoid going from one of the lights because it involved so much cutting into the dry wall and going around corners etc.

After doing the diagrams and getting suggestions from all of you, I have finally figured out that my first diagram was labeled wrong as far as the source was concerned. The source is from the bottom of the basement switch box and the second diagram in the boxed portion, for adding the light is exactly what I need to do.
Thank you all for your help and suggestions. I really appreciate them. As it turns out, I will probably have to cut a few holes in the drywall in order to get the wiring up to the sconce, (since there are at least two horizontal 2X4s between the switch and the sconce) but at least it is only in one wall and then it will be done with.

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