Phantom Voltages Phenomenon

Originally Posted By: jtedesco
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Quote:
Available for $15.00

National Electrical
Manufacturers Association
1300 North 17th Street, Suite 1847
Rosslyn, VA 22209
Tel: (703) 841-3200
FAX (703) 841-5900

www.nema.org



--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: dbozek
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Thanx for the info Joe. I ran across that very same problem the other day. Threw me for a loop at first because the circuit I was measuring was off icon_eek.gif I read a full 120 volts but I convinced myself that the circuit was dead when I read it to the other phase. For a minute there though I thought I was going bonkers


Originally Posted By: bhendry
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Never heard of a listed low impedance measuring device before.


I should be glad I still have a Simpson 260?

Anyone have the details on the low impedance meter?

Seems like a feature for a multimeter manufacturer - press this button - place 100k resistance or so across the probes and see what happens with the ghost.


Originally Posted By: jfarsetta
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In the context of what we do in the typical inspection, how does this pertain to us?


We follow a Standard of Practice.


--
Joe Farsetta

Illigitimi Non Carborundum
"Dont let the bastards grind you down..."

Originally Posted By: Guest
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old analog meters are much more likely to be low impedance. Digital meters are largely designed for electronic circuits and must have very high impedance to prevent damage to the circuit. To separate the two styles of meter like this is a broad rule of thumb as both styles exist both formats. A wiggy tester is a nice crude unit that works well for our purposes. That said, pretty much none of this has anything to do with what we do as home inspectors. I use my Sure Test to check voltage and even that’s stretching the job description.


Originally Posted By: dbozek
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There is always the two finger hot chassis check…umm nevermind…don’t even ask! icon_eek.gif


Originally Posted By: Mike Parks
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While this is not a HI problem, some here do look at commercial work.


I will let those who know more that me explain a "high" leg to those who add commercial inspections to their work. ![icon_eek.gif](upload://yuxgmvDDEGIQPAyP9sRnK0D0CCY.gif)

Mike P.


Originally Posted By: jbehling
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This would explain why my volt stick goes off sometimes when touching “dead” knob and tube wiring. eusa_think.gif


Originally Posted By: jpeck
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jbehling wrote:
This would explain why my volt stick goes off sometimes when touching "dead" knob and tube wiring. ![eusa_think.gif](upload://lNFeGuTetUAtwNVgUSOuUzgrGGK.gif)


Or maybe that leg is not really dead.

NEVER ASSUME it is not real.

ALWAYS ASSUME it is real.

PROVE to yourself that it is not real before thinking of it as anything but real.


--
Jerry Peck
South Florida

Originally Posted By: Ryan Jackson
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jpeck wrote:

Or maybe that leg is not really dead.

NEVER ASSUME it is not real.

ALWAYS ASSUME it is real.

PROVE to yourself that it is not real before thinking of it as anything but real.


Jerry....Have you been watching the matrix again?


--
Ryan Jackson, Salt Lake City

Originally Posted By: jfarsetta
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I’m waiting for Joe T’s reply…



Joe Farsetta


Illigitimi Non Carborundum
"Dont let the bastards grind you down..."

Originally Posted By: dbozek
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The high leg…not to be confused with high chair. As to not get tooooo technical here…typically it is found on a 3 phase system and it’s voltage is higher than the other two phases. On the outside, the power company typically marks the high leg with yellow tape. Depending on how high that leg or phase of voltage is, it may or may not be used to power any branch circuits. I have seen panels set up where every phase C space was blanked off due to the fact that phase C to neutral was 140 volts. Typically it is the phase C that makes the “high leg” voltage. It has to do with the type of transformer used and the configuration of such. Don’t quote me on this for I am a bit rusty with this theory but I do believe that a wye delta transformer will create one leg of ac voltage that is typically higher than the others. When reading the voltage across A to B, B to C and C to A, all readings seem to be normal. But when reading the high leg to neutral it is higher in potential than the other two phases.



You cannot help men permanently by doing for them what they should and could do for themselves. Abraham Lincoln

Originally Posted By: jtedesco
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icon_rolleyes.gif



Joe Tedesco, NEC Consultant


www.nachi.org/tedescobook.htm

Originally Posted By: jbehling
This post was automatically imported from our archived forum.



jpeck wrote:
jbehling wrote:
This would explain why my volt stick goes off sometimes when touching "dead" knob and tube wiring. ![eusa_think.gif](upload://lNFeGuTetUAtwNVgUSOuUzgrGGK.gif)


Or maybe that leg is not really dead.

NEVER ASSUME it is not real.

ALWAYS ASSUME it is real.

PROVE to yourself that it is not real before thinking of it as anything but real.


I had a situation recently where I tested some old knob and tube in a basement of a house, my volt stick said there was power. I advised my client to have a sparky come in to confirm, long story short, sparky says wires are dead..... wondered why my volt stick would go off then?


Originally Posted By: jtedesco
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jfarsetta wrote:
I'm waiting for Joe T's reply...


http://www.nachi.org/bbsystem/viewtopic.php?t=5323

![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)


--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: jfarsetta
This post was automatically imported from our archived forum.



Joe,


You opened the discussion and this thread by posting about phantom voltages. I am curious why you think we, as HIs, may run into this, how to check for it, and why you think its relevent to any inspector's COE.

Jerry, I know you want to jump in, and realize that your inspections are far and above the norm. Please refrain. I'd like to hear Joe T's answer, and not in the form of an invitation to his board.


--
Joe Farsetta

Illigitimi Non Carborundum
"Dont let the bastards grind you down..."

Originally Posted By: dbozek
This post was automatically imported from our archived forum.



In Joe’s defense, I’d like to say that perhaps he feels it is necessary for a HI to know this for safety reasons, especially if a HI uses a volt meter…umm like some here do. I don’t think, in my opinion, that Joe is throwing a lot of info out there to confuse anyone or to cause any harm. Most of what I read from Joe is professional, accurate and more importantly…it is related to safety. I think safety in your job as a HI as well as my job as a sparky is of the utmost importance when dealing with electrical circuits. The voltmeter thread is important to me as a sparky and to those HI’s that use a voltmeter. The graphic pics Joe tends to display here is in my mind a scare tactic to get everyone here to be extremely careful when dealing with live electrical circuits…anywhere. I know you would prefer that Joe, himself, answers this but you know me…I just had to stick my 2 cents in.



You cannot help men permanently by doing for them what they should and could do for themselves. Abraham Lincoln

Originally Posted By: jtedesco
This post was automatically imported from our archived forum.



jfarsetta wrote:
Joe,

You opened the discussion and this thread by posting about phantom voltages. I am curious why you think we, as HIs, may run into this, how to check for it, and why you think its relevant to any inspector's COE.

Jerry, I know you want to jump in, and realize that your inspections are far and above the norm. Please refrain. I'd like to hear Joe T's answer, and not in the form of an invitation to his board.


Joe F.

Dennis said it better than I, but so that you will understand why I posted the subject, first there were questions elsewhere on this forum that indicated the presence of voltages, and I remembered this NEMA bulletin.

I also searched and found the following discussion and believe that it will answer your questions too. It was too long to reproduce. I think the replies are genuine and I learned something too.

http://forum.doityourself.com/showthread.php?t=171224


--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: Mike Parks
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Jason


"wondered why my volt stick would go off then?"

Induction. The wire you chose to test was 'picking up' the wave from somewhere else.

You will get these false reading on three way switches (the travelers) also.

Take your ticker tester and walk under some of the big towers. It will buzz.

The tester should be used as a last test before 'working' on electrical not for testing. It tells you that there 'might' be electricity present not that it is present.

Mike P.


Originally Posted By: Mike Parks
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I got this same “Phantom” reading while replacing a service this week (the one with the Wadsworth 'sub’panel).


I installed a Square D disconnect outside and was checking the connections for 'crosses'.

In the disconnect my wiggy showed some voltage from a mount screw to where I was going to install the 'bonding' screw. When the bonding screw was installed the voltage went away and I read continuity only. No electrical connects to the exsisting electrical system were made. I showed this to the inspector and a friend of mine, another master, and we are still trying to figure this one out.

Mike P.