Would you please explain phantom voltage.

Thank You
Edward

edward.i think this link may help you.
http://www.nema.org/engineering/papers/PhanBull88.html

Edward,
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.

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.

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).]

Trumpy;
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??

I carry an old Square D "Wiggy" in addition to my high Z Fluke T5.
The "ghost" goes away with just a tiny load.

"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: http://www.tegam.com/datasheet/handtest/safety/sftyvolt.PDF



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

Trumpy,
Please define static induction.
Chris

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.

Along with the Xl/Xc coupled interference and the stored Capacitive charges from Xl/Xc coupling - already covered by members in this thread, there is another item which carries the term "Phantom" in it's description.

"Phantom Power" (may also be mistakenly reffered to as "Phantom Voltage", or "Phantom Current").

This is an intentionally designed scenario, which "carries" power to a certain device, via the "Signal" or "Data" wires that carry the devices data/signal to some type of processing device.

In a simple example, a Microphone and Audio Power Amplifier for the lead singer of a Rock Band make a great scenario!

The singer uses a 600 Ohm "Active" Microphone. The Microphone's internal Transducer will drive a signal out which is "Hotter" than a normal passive signal.
The Amplifier places a low power DC current on the Signal Line cable used to connect the Mic to the Amp.
The output sound signal from the Mic to the Amp is, of course, an envelope of AC frequencies.
The DC "Phantom Power" drives the "Active Pickup" (so to say) in the Microphone - thus delivering a much hotter signal to the Amp.

Some other examples include Active Guitar Pickups, "Carrier-Current" control / interfacing, some LAN hubs, various control equipment, not to mention POTS (Plain Old Telephone Systems).

Just wanted to point this out!

Scott s.e.t.

Scott35;
I noticed some different types of microphones, 57z, 58z and so forth. Do you know if this z is impedence? Does it have something to do with the internal transducer. I seen some mics for $50 and others for over $1000. Also I noticed a switch on a 16 channel sound board that said phantom on or off.

[This message has been edited by Wirenuttt (edited 01-10-2003).]

Have to throw my 2 cents in.

This “phantom voltage” and “phantom current” also I’ve heard it called “residual current” although can be innocuous in some cases but in other cases it can be very real and very deadly.
The voltage detector probe (“tic tracer” is one brand) mentioned in a previous post may indicates a voltage present on a conductor or cable assembly that is not connected to anything if that cable assembly is running along side energized conductors . In a 120v application the capacitive coupling places a very small voltage on the cable assembly which is not connected and as pointed out in other posts this very small voltage will be “swamped” if loaded by an analog meter, wiggy or other load. On the other hand if this same cable assembly or conductor is running alongside of some higher voltage cable for some significant length then the voltage now induced on the disconnected cable / wire can be significant enough to injure or kill. As scott35 pointed out due to XL and XC . Primarily capacitive coupling (I wouldn’t call or characterize it as “static induction”).

Real world example: I have had some qualified persons suggest that the voltage measured from the phase leg to ground of an ungrounded delta system is a “phantom voltage” and that they further believe that since the system is an ungrounded system (not connected to surrounding / earth via grounding electrode) that touching the phase leg (with that “phantom voltage” will not have any adverse effects since the ungrounded system is not grounded (connected to surrounding / earth) and there is no path back to the voltage source for current to flow. WRONG !! The capacitive coupling of all the motor windings and conductors running through the facility along side conduits (which are connected to surroundings / earth) as well as the transformer itself will create a capacitor effect (conductors separated by a dielectric / insulator) and will pass current. Anyone touching that phase leg in that ungrounded delta system will be touching an energized conductor WITH a REAL VOLTAGE on it and be electrocuted. Phantom Voltage my A*# !

Another real world accident I had the misfortune to investigate: Electrical workers (alleged qualified persons) replacing a feeder which was 13.8kv as I recall. Before they cut the cable a worker in the vault measured the current and said there was about 2 amps on the feeder circuit to which the foreman replied “That’s Just RESIDUAL CURRENT, go ahead and cut the wire”! Guess what happened –major arc flash. Thank goodness the worker did not loose his life but sustained injuries. HELLO! 2 amps at 13.8kv is equal to 27.6 kva that’s REAL POWER ! RESIDUAL CURRENT my A*# !

Voltage is voltage and current is current! Voltage is real and current is real! Voltage is the pressure that will cause current to flow if a path is provided and current at as low as about 30ma / .03 amps will electrocute a human adult,
Please Please gentlemen as professionals, lets stop perpetuating these misleading and inaccurate terms, at least for the benefit of the new folks were training and teaching in this profession.

Thank you for your indulgence and be safe out there !

OSHA Professor - Grizzy

Wirenutt:

"I seen some mics for $50 and others for over $1000. Also I noticed a switch on a 16 channel sound board that said phantom on or off."

phantom power is 48volts supplied by the soundboard to power some microphones(called condensing mics) these are more expensive but have much better frequency response also more fragile.

Cheaper but more robust mics are called dynamic mics. These don't need the phantom power to operate.

"different types of microphones, 57z, 58z and so forth."

?? Company called Shure makes mics with these model numbers if thats what your looking at.


Glenn

As OSHA Professor stated, these voltages are anything but phantom when it comes to medium and high voltage. I used to due regular PM and repair work on some large xfmrs, 26.4KV/600V feeding large DC drives(2 x 2500 hp). Full HV PPE is required to ground the primary side conductors even after LOTO of the line disconnect. You connect the ground clamp first, then swing the line clamp at the feeder connection and ZAP! There is enough stored energy due to the capacitance in the cable and xfmr to kill you. It's sobering to see a cable (open on both ends) crack an arc.