# Phantom voltage



## partimer31 (Jun 9, 2009)

How do you explain Phantom voltage measurements of an electrical wire?

And is what is the must likely cause of it?


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## brian john (Mar 11, 2007)

From a letter I wrote.

SUBJECT: Voltage Anomalies Phantom/Ghost Voltages
Job No. 6880


Dear Mr.:


On February 6, 2009 technicians from Mid-Atlantic Power Specialist were called to the above reference project to investigate possible stray voltage issues. In discussions with Colonial Electrical personnel it was determined the possible stray voltage issues were occurring with 120 VAC 15 amp switched receptacles. These receptacles are fed with a 14-3 with an equipment ground conductor NM cable. The only time there is an issue of concern is when the three way switch controlling the top Unit and were checked for this possible 
stray voltage issue. This issue was first noted per Colonial Electric personnel when the Prince Georges County electrical inspector (Authority Having Jurisdiction- AHJ) was performing an inspection of the receptacles in the individual units.


Voltage reading were taken on the receptacles with the top (switched portion) on and off, nominal voltages were noted with the receptacle energized (top and bottom). With only the bottom of the receptacle energized and the top half off from the 3-way switches voltage readings were noted in the 42 VAC - 84 VAC range.
These readings were verified with a calibrated Fluke 187 True RMS Multimeter, a Fluke 435 Power Quality Analyzer and a Simpson Model 260 (analog meter). In addition an Ideal 61-501 Receptacle tester was utilized to try and achieve the anomaly that brought this issue to the attention of the AHJ. With the Ideal 61-501 inserted in the outlet the center light dimly lights. When a Wiggy style tester (solenoid tester) is utilized there is no indication of voltage and the neon light (if present) does not illuminate. In this instance a Knopp k60 solenoid tester was utilized.

Voltage Anomalies
Page II


During these test with the Ideal 61-501 center light dimly illuminated a 12 VDC resistive element lamp was connected to the receptacle under test (with the receptacle de-energized) the 12 VDC lamp did not light and the Ideal 61-501 was no longer illuminated. With the Fluke 187 Multimeter measuring voltage and the lamp connected the voltage reading dropped to 41 millivolts AC (this result was the same for the Simpson 260 and Fluke 435). In addition with the Ideal 61-501 dimly illuminated jumpers were installed that permitted shorting the grounded conductor (neutral) to the opposite polarity of the receptacle together and through the technician’s hands, no shock was felt and in both cases the Ideal 61-501 lamp was extinguished.


This condition, reading voltage on a de-energized conductor to neutral or ground that is part of a multiwire cable or feeder in conduit where another conductor is energized is referred to by several terms in electrical literature Fluke refers to this as “stray or “Ghost” voltages, NEMA (National Electrical Manufactures Association) utilizes the term “phantom” voltages. *See attached documentation from Fluke and NEMA*


Stray, Ghost or Phantom voltages are a result of the test equipment utilized to perform the test. These instruments are high impedance measuring devices and the conductors in the cables are by nature of the design capacitively coupled. This issue is common and unavoidable by nature of the cables and is necessary as all conductors of a common multiwire circuit need to be routed tighter to avoid inductive heating. This issue has been known for years but seldom comes to light till such time as cases as this arise.

Ideal Industry was contacted regarding this issue and they are aware of the phenomena and its effect on their Model 61-501 receptacle and while Ideal has no documentation at present regarding this issue they do note in their application notes (attached) that this instrument is not for diagnostic work. From the application notes for the 61-501 Colum 1 Note- item 2.

NOTE: 

2_. Not a comprehensive diagnostic instrument, but a simple instrument to detect nearly all common_
_improper wiring conditions._


The Ideal applications engineer did inform me if there were any concerns we could not alleviate with our letter he would be happy to discuss this issue with Colonial Electric personnel or the AHJ regarding this issue.


To check the Ideal tester center light operation issue a test circuit was set up in our shop the results of this test is detailed in the table below. The test circuit was comprised of 50’ of 10-3 NM (the only available NM in our shop). The conductors were meggered at 1000 VDC prior to the test. The NM cable was laid in a straight line on the floor and the Black and Red conductors were connected to two separate single pole circuit breakers at 
208/120 VAC in a 3 phase 4 wire wye panel), the white/neutral/grounded conductor was connected to neutral termination bar in the panel and the bare grounding conductor was terminated on the grounding termination bar.
Voltage were measured and recorded and then the red conductor was removed from its circuit breaker and left in free air at both ends.
February 10, 2009
Colonial Electric Company Inc
Voltage Anomalies
Page III












In the Voltage Test Black Red Energized the Ideal 61-501 was connected with alligator jumpers to the black, white and bare conductor with correct polarity and the unit indicated CORRECT. The Ideal 61-501 was then connected with jumpers to the red, white and bare conductor with correct polarity and the unit indicated CORRECT. In the voltage test Voltage Test Black Energized, Red De-energized the Ideal 61-501 was connected with alligator jumpers to the black, white and bare conductor with correct polarity and the unit indicated CORRECT. The Ideal 61-501 was then connected with jumpers to the red (red was de-energized), white and bare conductor with correct polarity and the unit indicated center light dimly illuminated. When the red conductor was shorted to ground the center light on the Ideal 61-501 went out. This is what we expected and is what is consistent with the attached literature. The above test can be recreated with consistent results
at any location of your choosing


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## wiremanz (Aug 26, 2009)

Nice post.

Over the years I have found voltage on "supposedly" de energized conductors are often a result of inductance. This seems to happen more often on a multi conductor cable if the ground conductor physical connection to an actual ground becomes compromised. I've also witnessed the shields of twisted shielded pair wiring used for discrete digital control at 120Volts can carry nearly 100Volts if shield at either end is not grounded. Have seen this often in Pump Station control panels where someone forgot a shield at either end needs to be grounded.

Jeff Z.


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## RePhase277 (Feb 5, 2008)

Good answers above. I will also add that the atmosphere is responsible for at least some stray voltage. There is a huge potential between the sky and the Earth, and long conductors can become polarized by it, and have a small voltage at the ends. As in Brian's post, these voltages will drop to nothing if a load is applied. If a phantom voltage can actually light a test load, like a 12 V light, then it isn't phantom, and there is a problem somewhere.


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## partimer31 (Jun 9, 2009)

InPhase 277

"I will also add the atmosphere is responisble for at least some stray 
voltage"

I would agree, walk across a rug in the winter, then touch a metal
door knob. (humor)

But if I may ask, your atmosphere point, I find very interesting, do you
have a link, were I could read up this?

Thanks for you Post /S/ Robert


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## RePhase277 (Feb 5, 2008)

partimer31 said:


> InPhase 277
> 
> "I will also add the atmosphere is responisble for at least some stray
> voltage"
> ...


Start here: http://en.wikipedia.org/wiki/Sky_voltage


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## goose134 (Nov 12, 2007)

First, I'm glad to see that someone took the time to mention what they thought might be a problem. It warms my heart to think that the AHJ took the time to see if the switch actually made the outlet work, and then noticed when the light on his tester was dimly lit in the off condition. 

But Brian, great reply. Concise, thorough, and definitive. Nice.


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## JohnJ0906 (Jan 22, 2007)

Great post Brian. :thumbsup:


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## partimer31 (Jun 9, 2009)

*Is this you byline*

JohnJ0906

Quote: "it not my fault, it's no my problem, I'm not you solution". :laughing:

Is this your byline. 

(duck, typo overhead)


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## electricalperson (Jan 11, 2008)

brian. i want to do your job someday


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## JohnJ0906 (Jan 22, 2007)

partimer31 said:


> JohnJ0906
> 
> Quote: "it's not my fault, it's not my problem, I'm not your solution". :laughing:
> 
> ...


I really should give credit where credit is due - I stole that line from Celtic.... :whistling2: :laughing:


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## partimer31 (Jun 9, 2009)

*Avatars*

JohnJ0906 How many times have you change yours?


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## JohnJ0906 (Jan 22, 2007)

partimer31 said:


> JohnJ0906 How many times have you change yours?


Usually football season (something Ravens) and baseball season (Cal Ripken), with occasional variety in between.


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## psherrill (Jan 14, 2011)

*Phantom Voltages compromising control lines?*



brian john said:


> From a letter I wrote.
> 
> SUBJECT: Voltage Anomalies Phantom/Ghost Voltages
> Job No. 6880
> ...


Could capacitive coupling like this impact vdc control lines? I have a 48kw generator install with these types of anomalies on the control lines. The voltages appeared after several months of operations, now we are seeing some transfer issues (i.e. won't transfer to standby) The control line that is switched to ground when utility is lost shows 43vac when disconnected from both ends and at least one line energized.


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## Big John (May 23, 2010)

psherrill said:


> Could capacitive coupling like this impact vdc control lines? I have a 48kw generator install with these types of anomalies on the control lines. The voltages appeared after several months of operations, now we are seeing some transfer issues (i.e. won't transfer to standby) The control line that is switched to ground when utility is lost shows 43vac when disconnected from both ends and at least one line energized.


 That could absolutely explain the problem. The induced voltage doesn't care whether the conductor is supposed to carry AC or DC. If you put a conductor in close proximity to an AC source for a long enough distance, you'll get an induced voltage.

Had one just yesterday working on a 120VAC circuit where I read a solid 119 volts on an open conductor in a piece of tray cable. Cable was probably 100' long and there was another circuit in it powering some lights. Even when I put a load on the open conductor with a GFCI tester it only dropped down to 117 volts, but because it dropped at all, I knew it was induced.

-John


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