two-wire travellers and emf

[pierre]

Re: two-wire travellers and emf

Delfa
Education has a cost involved with it. If you or your men made the mistake of running the wrong wiring, the cost of replacement is an "educational" cost and hopefully a lesson learned and not to be repeated again. If you permit your men and yourself to 'stretch' the rules for monetary gain - well I think you should think about it again, as the lesson learned is wrong and will be perpetuated over and over again.

One thing about the cost of education... it will reap many future rewards that will be hard to see ($$$$), but will put the balance sheet in the POSITIVE for you and your company.

Pierre

 

[roger]

Re: two-wire travellers and emf

Jim, no it doesn't affect the NM, it produces EMF which is "suspect" of being a health risk (possibly causing leukemia in children) as well as causing noise on the system.

Roger

 

[a.wayne3@verizon.net]

Re: two-wire travellers and emf

Roger what about all those sub divisions throughout the U.S.A. that are right under buzzing high voltage systems.Does a 2 wire traveller pose the same risk ?????

 

[roger]

Re: two-wire travellers and emf

Allen, yes these areas are also in question. Whether it is the same risk I'm not sure, but proximity to the interior wiring EMF could be close to, or exceed the EMF from these exterior sources.

Karl Riley has a lot more information and a world more knowledge in this area than I do. I do know the theory behind the causes.

Concerning the health risks, I only know what I have read, some obviously biased and some just reporting the research.

Roger

[ January 18, 2004, 05:56 PM: Message edited by: roger ]

 

[jimwalker]

Re: two-wire travellers and emf

Just how close could one live to a sub station without any risk? Would 60 feet be too close

 

[roger]

Re: two-wire travellers and emf

At 60' I'd borrow (or buy, probably my next investment anyways) a Gaussmeter and take some readings.

After that you'd have to do some research and use personal judgement to decide if you considered yourself to be in a bad situation.

The bottom line is, the jury is still out on the absolute verdict.

Roger

 

[jimwalker]

Re: two-wire travellers and emf

A recent townhouse job 40 units was built so that about 4 units ended up so close that the noise from there cooling fans forced you to keep windows closed.The average unit was selling around $130,000 ,but these few went for about $100,000.Other than the noise i would be worried about long term.What happens should it be proved they are a health problem?

 

[hurk27]

Re: two-wire travellers and emf

Roger
Not to take the thread side ways but I few years ago I had a Greenlee tic-tracer the one with a sensitivity adjustment on it. one day I was at a house to find a covered up receptacle box and the thing would go off no matter where I held it. thinking that maybe week battery's were the cause I went out to my truck and installed a fresh 9 volt. then I turned it on and it still went nuts. just then I looked up and saw the HV transmission lines over head. I had to go back to looking for the bulge in the dry wall to find the plug as the tic-tracer was useless. I would hate to see what a gauss meter would show on that house or several other one in the same block.
These were line that ran from the generator plant on Lake Michigan to the south of us but why they allowed the subdivision to be built underneath them I have no clue.

 

[jxofaltrds]

Re: two-wire travellers and emf

Wayne

My ticker tester will not buzz until 20-22mg (this is under the towers).

The first time this happened I was walking my dog and I heard this beeping. I thought it was my cell phone. Sorry some of us are slow learners.

High voltage lines at the front of my property. 22-24mg under the lines. 600-900' away 1-1.5mg.

Do not ask me to go out in this cold and measure at 100'.

Mike P.

 

[hurk27]

Re: two-wire travellers and emf

Darn I guess I'll have to. Double darn I don't have my tic-tracer here LOL

 

[roger]

Re: two-wire travellers and emf

Mike and Wayne, don't go back out tonight, wait till tomorrow.

Roger

 

[hurk27]

Re: two-wire travellers and emf

This is the tracer I was talking about it is very sensitive. and will trace 24 volt circuits too.
Thank's Roger I won't

[ January 19, 2004, 09:25 PM: Message edited by: hurk27 ]

 

[karl riley]

Re: two-wire travellers and emf

Since I was away I just read this thread. Seems the 3-way situation has been well discussed. However you interpret the NEC, is the problem that of saving some pennies by using 2-conductor instead of 3-conductor for the travelers? The magnetic field can be huge with 2-conductor, depending on the load. Every wiring manual I checked shows using 3-conductor. Why not do it and not be called back later for whatever reason?

hbiss urges you all not to use a gaussmeter. This makes me feel like I am back in the middle ages. Imagine being told not to walk around with a voltmeter. And those weird clamp-on ammeters. Why do you know they are actually measuring the magnetic field and transposing it to an amp reading. Weird!!!

But to address some of the other questions. Power lines were assumed to be the main source of elevated magnetic fields in buildings until some of my colleagues and I found that misconnected neutrals and some water pipe grounding situations were by far - over 70% - the cause of elevated fields in buildings.

Of course a power line very near a building can give it a high field. Interestingly, net current comes into this also, since if a significant amount of the power line neutral is traveling in the earth there will be net current, which weakens much more slowly than a balanced 3-phase line.

About substations: the intrnal facilities do not generate much of a field outside the fencing; it is the lines coming in or out which are carrying the main field.

About gaussmeters: since a very accurate one now costs about $250, they are not such an exotic instrument any more. Some utilities use the $2,000 Emdex, but it is not more accurate, it just has a data-logging capacity. I use mine to make useful graphs of either time or distance.

Without a gaussmeter-refering to 3-way travelers - just clamp an ammeter around the travelers. The magnetic field at any distance will be twice the amps divided by howmany meters you are distant from the travelers. So 4 amps on the ammeter means 8 mG at 1 meter away.

I guess that's all for now.

Karl

 

[karl riley]

Re: two-wire travellers and emf

This thread is such a thorough discussion of 3-way wiring that I am reluctant to leave it before finishing the discussion.

Hbiss posted that 300-3(b) says that the grounded conductor must be run with the other conductors "where used". And he prefers not to use it. All 120V circuits use a grounded conductor. 240V may not. The question with the 3-way circuit is where you run the neutral, not whether you run it.

Do you run it with the hot or do you run it separately through the wall between switches or the receptacles feeding the switches?

Before the 1999 NEC NM was not excepted from 300.3(b). Why it was excepted in '99 I would be interested to know, as it seems to be a step backward. However, if you use this exception and run your neutral away from the hots (travelers) you also have to comply with 300.20(B). This requires you to cut a slot in any ferrous metal between the separated conductor and it's accompanying conductor/s, to reduce the heat buildup.

So if your traveler hot enters any ferrous junction box or fluorescent fixture without it's neutral you have to start cutting. But how do you do this if the neutral is 10 feet away in the wall. Any ferrous box the neutral goes into will also need a slot between it and the hot, so you have the same situation. The heat buildup that 300.3(B) is trying to avoid will occur, since the other conductor is far away. So how can this be Code compliant? Obviously they were not considering the possibility that one conductor would be run in an entirely separate path.

It was mentioned in this thread that if hot and neutral are derived from a single circuit maybe 2-conductor travelers are OK. But this means you have a circuit running through the wall with only one conductor carrying current, either the hot or the neutral. The traveler carries one current-carrying conductor and the circuit in the wall between the switches carries the other current-carrying conductor.

This sets up a large loop. The magnetic field inside a loop is large and very uniform, so the calculation of the magnetic field I mentioned in my preceding post has to be modified, since the field does not continue to weaken, but builds up again as it approaches the other side of the loop.

About liability, mentioned as a red flag by hbiss: no electrician is going to be sued for following the NEC. There may be liability issues in the future based on having knowledge of possible or probable health effects and then failing to use this knowledge in electrical installations, just as in the cigarette industry, but the electrician is protected by following Code. Many electricians create high fields by not following Code. Someday there will be a landmark lawsuit.

Meanwhile, Code allows you to use 3-conductor travelers in 3-way switching; the wiring manuals show it as the correct way, so why not do it?

That's it for me! As they say, thank you for your attention....

Karl

 

[ronson]

Re: two-wire travellers and emf

are all of you trying to tell me that i will still to need to rip out the 14/2 travelers & replace them with 14/3 in this 40 year old house i'm rewiring? that may be difficult on a couple of lighting ckts for a back room & the back porch. these ckts are behind some 3' ductwork that runs almost from one end of house to the other and is against where rafters & joists come together at back of house. will be hard to crawl back there. what makes matters worse, is that whoever ran hot to 3 ways, ran only the black from a receptacle, cutting off the neutral at source & in 3 ways box. this box is under where roof & joist meet. this house also has blocking. reference my "how does neutral work?" in "contracting & estimating" section for more info.

[ February 29, 2004, 12:40 AM: Message edited by: ronson ]

 

[jimwalker]

Re: two-wire travellers and emf

Ronson ,i don't believe this pertains to romex.My understanding is it causes a problem in EMT.

 

[roger]

Re: two-wire travellers and emf

Jim, EMF (as in part of the title of this thread) can be a problem in all wiring methods.

Inductive heating would not be a problem in NM.

Roger

 

[a.wayne3@verizon.net]

Re: two-wire travellers and emf

OK I have used 2 wire travellers allot over the years and have never had bad feedback,works fine.I agree that the neutral has to be from the same circuit.But all this about EMF causing problems health wise....If you are talking about high tension grids yes,but a 3way for a light ??
I won`t go there

 

[roger]

Re: two-wire travellers and emf

Allen, the EMF problem is not only a possible health problem, it also creates noise, interference, and other nuisances in electronic equipment.

Roger

 

[ronson]

Re: two-wire travellers and emf

roger, using 14/2 as travelers could very well be the source of the noise, interference, etc. that owners of 40 year old house told me they have been hearing on their cordless phone.