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#20100 - 01/08/03 10:46 PM phantom voltage??  
Edward  Offline
Joined: Dec 2002
Posts: 308
Would you please explain phantom voltage.

Thank You


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#20101 - 01/09/03 12:47 AM Re: phantom voltage??  
lighthouse  Offline
Joined: Jan 2003
Posts: 134
philadelphia pa 19125
edward.i think this link may help you.

#20102 - 01/09/03 01:30 AM Re: phantom voltage??  
Trumpy  Offline

Joined: Jul 2002
Posts: 8,217
SI,New Zealand
This phenomenom,could also be called an Induced Voltage, it is common with long cable runs and where cables are bunched together in an installation.
I have seen up to 98V AC, induced into cables,by static induction.
But it is at extremely low current, it is nothing that should be feared from a safety perspective. [Linked Image]

Let's face it, these days if you're not young, you're old - Red Green grin

#20103 - 01/09/03 08:15 AM Re: phantom voltage??  
tsolanto  Offline
Joined: Sep 2002
Posts: 131
Long Island NY
Any time a current is induced into a wire a magnetic field gets built up around the wire. If the magnetic field is in close proximty to another wire it can couple to that wire, thats how a transformer works. If you use a proximity tester (tick tracer) you can pick up these trace voltages. Sometimes ballasts and transformers can induce pretty high voltages on ungrounded metal conductors, enclosures, conduit etc. although the load carying capibilities is very small. You can read the voltage with a meter because of its high impedance. Just ground it and it disapates.

#20104 - 01/09/03 09:43 AM Re: phantom voltage??  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Another thing you'll notice is that the voltage you read depends upon the type of meter. As noted above, the high input impedance (typically 10 meg) of a digital meter results in a high reading.

If you swap over and measure using a traditional analog meter with a lower input impedance, you'll find that the reading drops substantially. In fact, because the input impedance of the meter varies from range to range, you'll find that the apparent voltage drops each time you switch to a lower range.

Where the voltage is caused by capacitive coupling due to proximity to an energized conductor, you're effectively forming a potential divider with that capacitance and the resistance of your meter.

[This message has been edited by pauluk (edited 01-09-2003).]

#20105 - 01/09/03 10:37 AM Re: phantom voltage??  
Wirenuttt  Offline
Joined: Nov 2002
Posts: 267
You mentioned static induction. I was at a manufacturing food processing plant about 10 years ago. All their machines had a static ground attached from the conduit to the machines. Do you know if that eliminates phantom voltages to zero or was this just because of a hazordous location with flying combustables in the air or both??

#20106 - 01/09/03 11:36 AM Re: phantom voltage??  
electure  Offline

Joined: Dec 2000
Posts: 4,260
Fullerton, CA USA
I carry an old Square D "Wiggy" in addition to my high Z Fluke T5.
The "ghost" goes away with just a tiny load.

#20107 - 01/09/03 12:41 PM Re: phantom voltage??  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
"Tegam" makes a family of single function, digital voltage meters.
The Voltman Model 125 is a low impedance meter designed to eliminate "phantom voltages".

try here:

[This message has been edited by Redsy (edited 01-09-2003).]

#20108 - 01/09/03 04:03 PM Re: phantom voltage??  
Chris Rudolph  Offline
Joined: May 2001
Posts: 160
Winter Park,Fl USA
Please define static induction.

#20109 - 01/09/03 08:50 PM Re: phantom voltage??  
Gwz  Offline
Joined: Apr 2002
Posts: 197
Many a lineman has died from this "static" voltage on high-lines. Conductors that are run parallel ( for miles ) with energized circuits on the same poles or towers or even close-by structures build-up a lethal voltage.
These conductors must be grounded, near-by the person working on those lines.

Grounding the conductors being 'worked on' a mile or so away from the work site can have lethal voltages.

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