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#94116 - 07/07/05 07:20 PM 3-way switch legs  
gserve  Offline
Joined: Mar 2003
Posts: 92
I have a customer that wants to switch there paddle fan/light combo with 2 switches at each entrance to the room(so that the fan or light can be switched separately at each entrance)I have never seen this done.If I use a 14/2 and 14/3 for travelers and neutral between switch boxes and feed 1 end and take a 14/3 to the fan/light combo does this meet code? The 14/3 will be used for travelers and neutral and the 14/2 for the other set of travelers.What do you think? Any other way to do this?

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#94117 - 07/07/05 07:54 PM Re: 3-way switch legs  
Larry Fine  Offline
Joined: Feb 2005
Posts: 693
Richmond, VA
I'd start by asking what there is now. Fan box already installed? Is it fed always hot? Or are you starting from a wall switch?

If this is a new installation, the best method is to feed the first switch via a 14-2, run a 14-3 between switches, and a 14-2 from the second switch and the fan.

There are several other ways to wire 3-ways, too. Again, it depends on the present conditions and the wire-routing pathway. Tell us more.

Larry Fine
Fine Electric Co.

#94118 - 07/07/05 08:23 PM Re: 3-way switch legs  
MI Sparky  Offline
Joined: Jul 2005
Posts: 14
Fenton, MI
nothing wrong with that at MUST mark the white in your 14-2 traveler as a hot.

I thought that was off!!!!

#94119 - 07/08/05 01:15 PM Re: 3-way switch legs  
John Crighton  Offline
Joined: May 2005
Posts: 177
Southern California
MI, are you sure about that? The end result is that the hot and neutral for one of the circuits are in different cables.

So, how close together would those cables have to be? Would it be OK for them to run around opposite sides of the room? I don't think so.

The problem is that the fan has only one neutral connection for both the fan and the light. Therefore you'd have to start with the 14-2 branch circuit to the fan box to make the neutral connection. Then run ONE 14-3 from the fan box to the first switch box (hot, fan, and light), and continue with TWO 14-3 to the second switch box (each having a hot and two legs).

Make sense?

#94120 - 07/08/05 02:51 PM Re: 3-way switch legs  
gfretwell  Offline

Joined: Jul 2004
Posts: 9,057
I think the easy answer is to run the 4 travellers in a piece of Smurf tube between the switching locations. Then wire count is not an issue. 14-2 into the first one, 6 wires (5 current carrying plus ground) in the smurf to the second switch location and 14-3 out to the fan/light.

Greg Fretwell

#94121 - 07/08/05 05:53 PM Re: 3-way switch legs  
MI Sparky  Offline
Joined: Jul 2005
Posts: 14
Fenton, MI
You know John that is correct, I never thought of it that way, our company had wired a certain model of a house in the same way....not for fan though, and the inspector never said a word. He could just run twin 14-3's and tie the neutrals in at both ends!

I thought that was off!!!!

#94122 - 07/08/05 08:41 PM Re: 3-way switch legs  
poorboy  Offline
Joined: Jun 2005
Posts: 124
Central Maine
John, why is that an issue? A switch leg has no neutral either.

#94123 - 07/08/05 09:00 PM Re: 3-way switch legs  
John Crighton  Offline
Joined: May 2005
Posts: 177
Southern California
MI, you can't just tie the two neutrals, either, because the current will be divided between them, and only half of the current will return in the same cable as the hot leg.

poorboy, you're correct that a 3-wire cable with 2 switch legs and a hot (or load) wire has no neutral, but there is still an equal current in both directions -- "out and back".

We're all familiar with the requirement for the hot and neutral to be carried in the same conduit to prevent inductive heating of the metal. A more general statement of that requirement is that any current-carrying conductor has to be closely paired with another conductor carrying an equal and opposite current. The intent is to produce a net magnetic field of zero, whether the conductors are in conduit or in open space.

#94124 - 07/09/05 08:10 AM Re: 3-way switch legs  
dmattox  Offline
Joined: Oct 2004
Posts: 265
Anaheim, CA
The code doesnt require a neutral in romex if I remember right. But I don't do residental.

#94125 - 07/09/05 08:45 AM Re: 3-way switch legs  
winnie  Offline
Joined: Sep 2003
Posts: 649
boston, ma
For _non-metallic_ wiring systems, I do not belive that there is a _requirement_ that all conductors travel in the same raceway/cable assembly. At some point one hits performance requirements, such as having a low impedance fault current path...but you would have to have a pretty extreme situation for the inductive impedance of the loop to make a difference.

IMHO it is a very good idea to minimize loop area, for example to minimize 'emf' (no proven dangers here, but why go out of ones way to make a potential threat worse when doing things right essentially eliminates the issue). But I see no significant difference between running a _non metallic_ 14-2 and 14-3 side by side, versus running a single 14-5. The junction boxes would either need to be non-metallic, or both cables would need to enter through the same cable clamp (using a clamp suitable for two cables).

I am in total agreement that for metallic wiring systems, the inductive coupling to the conduit or cable armor is a significant problem, and that this would be a code violation.


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