Three way switch layout

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  #1  
Old 07-11-06, 07:07 AM
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Three way switch layout

This is a remodel, I need unswitched power at both SW1 and SW2.

Anything wrong with wiring it like this?


SW2 (20 cu in)

12/2 power in
12/2 power out
12/2 travelers out

SW1 (3-gang)

12/2 travelers in
12/2 switched power and neutral to light
12/2 power in (for other switches)

Light

12/2 switched power and neutral from SW1

Basically, power is coming from SW2, travelers to SW1, SW1 provides switched power and neutral to the light.
 
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  #2  
Old 07-11-06, 07:42 AM
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Yes and no.

If the boxes are metal then there is a problem. If the plastic then this okay, but not desirable.

Do the right thing.

Go to the store and buy 12-2-2 and use it instead of two runs of 12-2 between the switches.

OR

Use 12-2 to carry unswitched power between the switches for the other switches and use 12-3 to carry the two travelers and the neutral between the switches for the switched circuit.
 
  #3  
Old 07-11-06, 07:59 AM
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Bob,

thanks for the response, I still don't quite understand when its approriate to use 12-2-2 vs 2 12-2.

I didn't choose the 2nd option because of box fill at SW2.

Currently, unswitched power for both switches come from different JBs (same circuit). I couls switch this though. This is under permit and will be inspected so I wanted to get it right.

All boxes are plastic.
 
  #4  
Old 07-11-06, 08:12 AM
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The current in each direction in a cable or raceway needs to balance.

In your situation, when the light is ON you will have unbalanced current in both cables. The 12-2 with the travelers will have current in one direction only, and the cable with the unswitched hot and neutral will have additional current on the neutral (from the light). When the light is off there is no issue.

The underlying problem is the em field caused by the current. With metal junction boxes this is an issue. With plastic boxes this is less of an issue, as long the two cables run together.

However, an inspector seeing that you cut this corner may dig deeper and look for places where you may have cut a corner a little too much.


*****

I have re-read your original post. I am now confused. in the first 12-2 you have the two travelers. What do you have in the second 12-2 other than the neutral?
 
  #5  
Old 07-11-06, 08:19 AM
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This is what I have

SW2 (20 cu in)

12/2 power in from JB1
12/2 power out to JB 3
12/2 travelers out SW1

SW1 (3-gang)

12/2 travelers in from SW2
12/2 switched power and neutral to light
12/2 power in (for other switches) from JB2

Light

12/2 switched power and neutral from SW1

Currently, the way it is planned only 1 12-2 runs between the switches.
 
  #6  
Old 07-11-06, 08:27 AM
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There is no way what you have is safe or will pass inspection.

Change that piece of 12-2 between the switches to be 12-3, wire it properly (so that the 12-3 carries the travelers and the neutral) and be done with it.
 
  #7  
Old 07-11-06, 08:40 AM
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Thanks for the explanation, I understand the need to balance current in a cable/raceway now.

Suppose I use 12-2-2 to provide unswitched power and travelers from SW1 to SW2 (your option 1) isn't this unbalanced, since you have no neutral returning also?

Would the simplest way to run this be 12-2 from SW1 to SW2 for unswitched power/neutral and 12-3 for the travelers and neutral.
 
  #8  
Old 07-11-06, 08:46 AM
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All of my solutions are balanced.

Using 12-2-2 would allow you to eliminate the separate power feed from JB2 to SW1. Two of the wires are the travelers; one is the neutral and the other is the unswitched hot wire.

Using 12-3 would require that you keep the feed from JB2 to SW1, for the other switches and their loads. Two wires would be the travelers; one would be the neutral. As SW1 you must keep loads separate.
 
  #9  
Old 07-11-06, 09:01 AM
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Alright, thanks again, I learned something useful today. I was making the assumption that the unswithched power and neutral balanced eachother. After thinking about it, I understand how this was an incorrect assumption and you are correct.

Keep sharing the knowledge.
 
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