Travelers in separate conduit?

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Ron,
Good research.

Just as a comment:
This "Switch loops do not require a grounded conductor" quote
does not catch the idea that the returning 'switch leg'
is the current balancing conductor.

Just commenting, as I am sure you know this.
 
glene77is said:
Pierre,

I agree that a two pole circuit may not require a neutral.
OTOH, a switch loop and two returning switch legs would balance current flow.
I am trying now to imagine a 3-way circuit where there would be NO balancing current flow.
Oh, yeh, the infamous 'California 3-way' (which is not code any more).

Just to show how friendly these comments are meant to be,
let me remind you of the old country 3-way made with several strings
tied between a pull-chain fixture and each door-jamb. My grand-daddy's favorite!
Of course, there was no return wiring there, ha.

To be more serious, though:
From my calculations, which I did for my boss after a similiar comment,
the difference between D.C. resistance and 60Hz A.C. Impedance
is about .017 percent.
That makes me think that impedance is not an issue.

I have heard your comment before, but still don't understand where it would apply.
In a Radio frequency circuit, I would buy it in a New York Minute.

Your comments always catch my ear. Try me.
Click to expand...


Glenn thanks for the comments

I should have said, maybe I did don't really remember.

But there needs to be a grounded conductor of that light circuit or the switch leg returning with it in the opposite direction one or the other.

And I only think the impedance would be a problem in the worse case which would be a extremely long circuit and loaded to the gilles. :)
 
glene77is said:
Pierre,



To be more serious, though:
From my calculations, which I did for my boss after a similiar comment,
the difference between D.C. resistance and 60Hz A.C. Impedance
is about .017 percent.
That makes me think that impedance is not an issue.

Your comments always catch my ear. Try me.
Click to expand...




Impedance issue:
Separating the switch leg from the travelers creates more impedance in the circuit. Add length of circuit conductors and there may be enough impedance in the fault return circuit to impede the operating efficiency of the overcurrent device.
 
Michael

I know pierre, Glenn and myself would like to know the results of your test.
Every one knows where we stand.

I'm standing by, Thanks :)
 
Glenn

Was this your Grand-dads switch?
21.gif



Click here please give a minute to download
 
The problem is not with the switch it is with the basic understanding of electrical theory from 1 amp to 1000 amps you are asked by the nec to run the Hot side conductors with the return line (neutral)conductors along with any grounding conductors for one simple reason.
Equal and opposite magnetic fields will cancel each other. When you run a circuit out in different conduits or metalic raceways you will create a single turn transformer which will heat up accordingly to the severity of the current flow.
Who here is qualified to make a safe determination?? Just install it to the code. That is why it is there to take the guess work out of the equation by untrained persons.
 
ronaldrc said:
... worse case ... extremely long circuit and loaded to the gilles. :)
Click to expand...

I like that "Gillies", you must be a poet on the side!

Anyway, say E(applied)=120V, I=20A, and R=2ohm per 1000 ft,
and the return path is another 1000 ft.
I calc the available voltage at the load would be 40 V.
E(vd) = 20 Amp * 2 Ohms (per thousand) * 2 (thousand feet) .
I used the 'coated conductor' column
which is 2.01 to 2.05 Ohm per thousand feet.

I would say that in a long circuit, say 5000 ft out&back,
which totaled 5 Ohms, there could be a total current flow of less than 20 Amps,
and the OCPD would not trip.
That means that a hot to neutral fault would not trip the CB.

Is that the way you would figure Voltage Drop,
and is that the effect you expected ?
 
Glene,
Does that include the increased impedance from the inductive reactance that results from the current flowing on conductors that are physically separate from each other? There is a table in the IEEE green book that says the impedance doubles when you take the separation of the supply and return conductors from 2" to 30" (note from memory, and the numbers may not be exactly correct). I would expect that if the two paths are separate and in ferrous raceways the increase in impedance would be even greater.
 
Glene, I should have said loaded to the gills

I know I have a problem when I feel a hot conduit. I wonder what is the cause of this, is it wired wrong or just gotten overloaded from additions through the years.

Or maybe someone has run a switch leg by itself ?

If they'd done it to code it wouldn't be running hot. I know the NEC is not perfect but this one about eddy current makes sense.
 
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I had a situation similar to this in an office building in Nashville, TN. The Electrician ran the travelers for a three way switch that controlled the lighting for a half of a floor of an office building separately, from switch to switch in MC cable.

Our client called and said that he was having problems with Monitors flickering and office staff not wanting to sit in certain areas of the office.

I had purchased Karl Riley's Book "Tracing EMF's in Building Wiring & Grounding" and a Gauss meter about five months prior to this call so I flew down to the jobsite to try out the new information.

After meeting with the tennant and walking through the office with the Gauss meter I could tell exactly where the elevated magnetic field was (reading of 15mG to 25mG at desk level up to 72mG at floor level).

We then went down to the tenant on the floor below and checked his levels and noticed that the readings where higher the closer we got to the ceiling. Turns out the Lawyer on the floor below used a different electrical contractor to complete their tennant finish and they rand the travelers from switch to switch separately. This caused a very large magnetic field on the floor above which was corrected.

Not sure this is exactly relevant but it is an interesting aspect of what problems can arise when you run two wire travelers.

-Ed
 
Ron,
Michael still has a good comment.
We don't always answer each others question, directly with good numbers,
but we all can think twice about these important issues.
I alway try to err on the safe side.

BTW, I have been unable to download your picture.
Seeing your art work avatar, I am confident that it's good.
 
just getting ready to ask if maybe you all knew something I didn't,
like maybe it was in Canada.

Anyway I found this I knew it was a violation and had to find it.

so this says that its not a viotation
 
Shaw

No it is a violation

NEC_300.20(A).jpg


Glene

Michael made very good point, I agree with him it is a NEC violation to run the switch return without the neutral or the reverse return switch leg one or the other.

Rather its dangerous or not I will install it according to NEC requirements.
 
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