Using 12-2 for travellers between two 3-way switches

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kwired said:
in the switch loop current on one conductor is flowing the opposite direction of the other and equal amount thus they cancel. Same with three wire cable to a end of line three way switch. two conductors are carrying current when the load is energized, current is in opposite direction on each conductor and equal amount.

Add: with the two wire traveler you have current flowing only on one conductor at a time and no other carrying equal and opposite current within the cable or raceway.
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So what you are saying is that the switch leg is affecting the hot in exactly the same manner a neutral would?
 
K8MHZ said:
So what you are saying is that the switch leg is affecting the hot in exactly the same manner a neutral would?
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Yes. Clamping an ammeter around the cable you will read a net of zero. If you do have a net current by clamping a meter around the cable then not all current entering the cable returns through same cable, and you will have a net magnetic field around the cable.

I do believe that this is part of the reason for the requirements of 300.3(B)
 
K8MHZ said:
Then this is bad, too, then?

View attachment 5714
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The switch loop, in your diagram, has zero net magnetic field when you measure it for electromagnetic field a few inches away from the cable.
K8MHZ said:
How is running a two wire traveler any different than only running the hot and the switch leg to the switch? Neither have a neutral to cancel them out.
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Look at the current path in the switch loop in my diagram below:

TwoConductorNM3-wayfeedatlight_web.jpg


The current, to run the lamp, goes in a big loop around a room, or space, that can easily include people within it. The current loop is a single winding of wire around and air core inductor. The magnetic field created is concentrated in the center of the loop, that is, of the room, of the space.

Edit to add: I like to think, even though there is EMF between the two conductors inside a cable, it is hard for a person to get into that little space of unbalanced field. The EMF problem occurs when a person can place themselves inside an inductor.
 
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al hildenbrand said:
Looking at the diagram that I just posted, just cut in a 4-way switch anywhere along the travelers, as many times as you want.

Each 4-way then has 2-conductor NM in and 2-conductor NM out.
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That was my point, if you can use the 12-2 here why couldn't you use it without the 4-way?
 
Little Bill said:
That was my point, if you can use the 12-2 here why couldn't you use it without the 4-way?
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Ahh. :dunce:

I missed your thrust in #22. I agree that simple white conductor re-identification is all that is needed. 2011 NEC 200.7(C)(1)
 
Little Bill said:
That was my point, if you can use the 12-2 here why couldn't you use it without the 4-way?
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If you run two conductor cables between the 3 ways you would have one weird circuit. The feed would be at the light and you would run hot conductor down to one switch and the return down to the other switch with 2 way between them--- I am not sure if that would create emf's every other way I can think of will cause emf's.
 
Dennis Alwon said:
If you run two conductor cables between the 3 ways you would have one weird circuit. The feed would be at the light and you would run hot conductor down to one switch and the return down to the other switch with 2 way between them--- I am not sure if that would create emf's every other way I can think of will cause emf's.
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That's not how I would wire one. Just saying I didn't see any difference in cutting in a 4-way and using 12-2 or just having 12-2 as travelers without the 4-way. Have you always run 3-wire for 4-ways, even before a neutral was required (2011) at switches?
 
Dennis Alwon said:
If you run two conductor cables between the 3 ways you would have one weird circuit. The feed would be at the light and you would run hot conductor down to one switch and the return down to the other switch with 2 way between them--- I am not sure if that would create emf's every other way I can think of will cause emf's.
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If you can clamp a meter around a cable and not read zero while loaded you have emf"s
 
roger said:
As Dennis said you should use a three conductor cable (if using a metalic cable or raceway you have to use three conductors) see Ronald Colemans interactive fourway by clicking the link below which is wired as Dennis pointed out.

http://home.comcast.net/~ronaldrc/wsb/a4.htm



Roger
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If using I am using romex or MC I always run three wire between switches, but in conduit I usually only have the travelers in the pipe going to the 4-way. I always understood this to be okay.
 
ActionDave said:
If using I am using romex or MC I always run three wire between switches, but in conduit I usually only have the travelers in the pipe going to the 4-way. I always understood this to be okay.
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It depends how the rest of the circuit is wired. If you run 4 wires in a conduit t the 4 way switch you may be okay. How is the circuit wired that you are talking about.
 
Dennis Alwon said:
It depends how the rest of the circuit is wired. If you run 4 wires in a conduit t the 4 way switch you may be okay. How is the circuit wired that you are talking about.
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I agree. Dave, you would have to have the travelers going and coming in this conduit, IOW's as Dennis says, four conductors total.

Roger
 
al hildenbrand said:
The switch loop, in your diagram, has zero net magnetic field when you measure it for electromagnetic field a few inches away from the cable.
Look at the current path in the switch loop in my diagram below:

TwoConductorNM3-wayfeedatlight_web.jpg


The current, to run the lamp, goes in a big loop around a room, or space, that can easily include people within it. The current loop is a single winding of wire around and air core inductor. The magnetic field created is concentrated in the center of the loop, that is, of the room, of the space.

Edit to add: I like to think, even though there is EMF between the two conductors inside a cable, it is hard for a person to get into that little space of unbalanced field. The EMF problem occurs when a person can place themselves inside an inductor.
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Wouldn't the net sum inside the loop be zero? And highest at the outside of the loop? (Adjacent rooms, for instance.)
 
It depends how the rest of the circuit is wired. If you run 4 wires in a conduit t the 4 way switch you may be okay. How is the circuit wired that you are talking about.
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Last time I did this it was a green house that had four entrances.
Row of lights across the ceiling, one 1/2" emt dropped down to each switch.
Hot and Neutral stay at the ceiling, drop a common and two travelers at each end, travelers only at the 4-ways.
 
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OK, so hoping you can make out my drawing, more questions.

View attachment 5717


The sketch shows a total of 4 pieces of 2 wire Romex. (Not counting grounding wire)

1) From panel to box that the light is in.

2) From the box that the light is in to a 3/way on the north wall.

3) A traveler from the box on the north wall to a box on the west wall.

4) From the box on the west wall to the light.

#4 is circled at each end. The circles labeled A and B are two, two wire cables run next to each other.

Question 1: If the installation in the drawing has the cables that run next to each other close, but not bundled, how does that affect the EMF to the exposed beings?

Question 2: If the cables indicated at point A and point B were replaced with 4 conductor cables, would that make the EMF go away? After all, if you clamped that 4 wire cable, you would get net zero.

Question 3: If you were to separate any two cables and clamp just one and see a reading, then at the same point not separated them and clamp the two cables at the same time, which reading would be the best indication of the actual EMF received by the beings inside the structure?

Question 4: If you were to bundle the cables together to well that the only way you could clamp them would include both cables and got a reading of zero, would that mean that the circuit was EMF generation free, even though made entirely of 12 conductor NM?
 
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K8MHZ said:
Wouldn't the net sum inside the loop be zero? And highest at the outside of the loop? (Adjacent rooms, for instance.)
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To imagine the answer, consider the loop in my diagram to be a circle of radius R.

On the out side of the circle, at a distance of R, there is a circle that will have some of the magnetic field. The circle has a length of Pi x 4R = C. C is a much larger region than the point in the center of the current loop.

Now to be clear, all the magnetic field on the outside of the current loop stretches, theoretically, all the way to infinity, while all the magnetic field inside the current loop goes through the cross sectional area of only the circle's area A = Pi x R squared.

The amount inside area A is equal to the amount of magnetic field outside the circle, an area that is inifinite.

The magnetic field is denser inside the loop than outside.
 
K8MHZ said:
Question 4: If you were to bundle the cables together to well that the only way you could clamp them would include both cables and got a reading of zero, would that mean that the circuit was EMF generation free, even though made entirely of 12 conductor NM?
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If all conductors read a current of zero when measured together you have no EMF and no net currents flowing.

This is the method I use when trouble shooting EMI issues. I start at the panel and using a flexible clamp I read all the branch circuit and feeder conductors together, (zero sequencing) if I read current I start looking at circuits one at a time using the same method until I find the one(s) that do not read zero.

Roger
 
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