3-way switch question (sw-light-sw)

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Old 08-24-15, 02:52 PM
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3-way switch question (sw-light-sw)

When you look at a drawing of two 3-way switches with the light fixture in between, there doesn't seem to be a return wire from the second switch. The white from switch one ends at the light fixture and the white from switch two becomes a white-painted-black and wirenuts back to the red wire that connects to switch one.

Am I correct? Is this the best way to do this?

Is it correct that you cannot do sw-light-sw beginning with the 2011 NEC if there is no neutral wire in the switch boxes? If so, what do you do?

Gary
 
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Old 08-24-15, 03:25 PM
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You can use 4-condubtor cable (black, red, blue, white) instead of 3-conductor cable. Please post the diagram you are referring to so we can better help you.
 
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Old 08-24-15, 05:06 PM
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There are many ways to wire a three way circuit. In my diagram is the ideal way. Power comes in at one switch and the lights connect at the other switch. There is neutral at both boxes.

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Old 08-24-15, 08:05 PM
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I now see that my first description was wrong.

Here is my configuration. The white from the panel ends at the light fixture and the white from switch two becomes a white-painted-black and wirenuts back to the black wire that connects to the corresponding screw on switch one. Is this out of code as of NEC 2011?

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Last edited by GaryMN; 08-24-15 at 08:51 PM.
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Old 08-24-15, 08:49 PM
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Why do you want the light between the switches. The way PJ shows meets code and is easier.
except on another drawing the white from switch one ends at the light fixture and the white from switch two becomes a white-painted-black and wirenuts back to the red wire that connects to switch one.
Three thoughts on that:
  • The NEC does not specify colors used on 3-way. It is Installers option.
  • The NEC requires a white not used as a neutral be remarked any color but green or gray.
  • As to "white from switch two becomes a white-painted-black and wirenuts back to the red " Not sure I understand. I'd need to see the diagram but it may have to do with where the power comes in.

The diagram you posted would meet 2011 code if you used a 4-conductor cable instead of a 3-conductor cable to the second switch.

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Last edited by ray2047; 08-24-15 at 09:17 PM.
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Old 08-24-15, 09:13 PM
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The first switch is original with the house. It is 3-wire, run inside a sheetrock wall, located near the house entrance from the garage. It leads to a ceiling-mount light fixture, I'm trying to locate a second 3-way switch near the other door at the opposite side of the garage.

Thanks for the markup showing 4 wires. In box two, what do you do with the white wire?
 
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Old 08-24-15, 09:19 PM
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You already have the three wire cable from your original switch to the light. You are converting that cable to operate a three way switch system.

That begs the question...... what is that three wire cable doing now ? Why was three cable run if all three conductors weren't in use.... a spare ?
 
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Old 08-24-15, 09:50 PM
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good question

Pete, the red was just wire-nutted inside the ceiling box. I am the third owner of this house and wasn't around when it was done. I assume the electrician needed to go get more wire, a switch and a handy box, but it was Friday afternoon and Miller Time and ... now it is 25 years later and I just discovered the situation. I would like to add the second switch.
 
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Old 08-24-15, 10:01 PM
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A spare..... that was lucky on your part.
 
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Old 08-24-15, 10:10 PM
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what do you do with the white wire?
Nothing unless you install an electronic switch that needs it. Look close at the picture and you will see I put a wire nut on it at the switch. Also note I did connect it to the neutral at the light. (The red dot indicates a connection.)
I assume the electrician needed to go get more wire, a switch and a handy box, but it was Friday afternoon and Miller Time and
Or it was set up so at a later date a fan with light on two separate switches could be installed later.
It is 3-wire, run inside a sheetrock wall, located near the house entrance from the garage.
If you have an unfinished space above or below it is easy to fish a cable without disturbing the wall. Even with the 3-conductor cable I'd probably go ahead and use PJ's method. 4-conductor cable is more 3-phase commercial than residential and may be hard to find in less than a whole roll length.
 
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Old 08-24-15, 10:18 PM
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So the white wire in the second box is for future use?

In my case would there be an easier way than what is shown in the diagram?
 
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Old 08-24-15, 10:22 PM
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So the white wire in the second box is for future use?

In my case would there be an easier way than what is shown in the diagram?
Yes and yes. See the edits I made to my previous post while you were replying.
 
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Old 08-24-15, 10:26 PM
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In my case would there be an easier way than what is shown in the diagram?
In which diagram ?

If you want to be code compliant..... you need to use four wire cable and follow Ray's diagram.
If you don't want to be code compliant you would use three wire cable and follow your diagram.

That's it.
 
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Old 08-24-15, 10:59 PM
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Or use PJ's diagram. As I wrote in my edit of post #8 that is what I'd do if there was an unfinished space above or below.
 
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Old 08-25-15, 04:53 AM
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Great advice. Many thanks for all your help.
 
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Old 08-27-15, 12:26 PM
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One rule is that the wire coming back to bring power to the light fixture (to its black lead or hot terminal) may not be white.

It is best to run the 3 conductor cable nonstop from one switch box to the other. If the best route goes to the light fixture then this cable can pass by the outside. Then run a 2 conductor cable from the second switch to the light. The result is topologically the same as PJMax' diagram above. This method avoids having to scrounge around for 4 conductor Romex.
 

Last edited by AllanJ; 08-27-15 at 12:56 PM.
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