Phantom voltage

Phantom voltage (sometimes referred to as "ghost voltage") is voltage that appears in an electrical conductor such as a wire, even though the wire is disconnected from an electrical circuit. The term is often used by electricians, and might be seen, eg, when measuring the voltage at a lighting fixture after removing the bulb. It's not unusual to measure "phantom voltages" of 50-90 volts when testing the wiring of ordinary 120V circuits.


Causes of phantom voltage may include:

*Capacitive coupling in which there is capacitance (a build up of opposing electric charges) between the conductor in which the phantom voltage is detected and nearby circuitry.
*Inductive coupling in which the magnetic field produced by current flowing in a nearby circuit induces current flow in the conductor where phantom voltage is detected.

Capacitive phantom voltage

Two parallel wires, insulated from each other but running side-by-side, effectively form the plates of a capacitor. If an alternating current (AC) is applied to one of the wires while the other wire is not connected, then AC voltage will tend to be capacitively coupled to the disconnected wire. If there are no other wires nearby this coupling will be nearly complete, and the voltage measured on the disconnected wire will be nearly the same as on the "live" wire. However, if there are other wires nearby (such as a ground wire in the same cable) then in effect a capacitor voltage divider may be created, and the voltage on the disconnected wire will measure somewhere between the "live" wire and the other wires.

While the voltage produced by capactive coupling may be startlingly high the amount of capacitance between the wires is typically quite low and incapable of supplying significant amounts of current. [cite web
title = Phantom Voltages
accessdate = 2008-01-08
] As this term is used by electricians and engineers, "Phantom Voltage" refers to inductive coupling.

Inductive phantom voltage

In these cases, magnetic fields from an adjacent wire or other voltage source (such as a high tension tower) induce current and therefore voltage on the tested wire. This inductive coupling is enough to cause a fluorescent tube to glow when placed within the magnetic field of a high tension tower.

Other meanings

"Phantom voltage" is also a term used in audio engineering where a voltage is applied between the ground wire and both wires of a balanced audio line, in order to provide power for a microphone or other device. This concept is more properly referred to as "phantom power".)

"Phantom voltage" is also sometimes used to describe a situation where a voltage develops between the grounding conductor of an electrical installation and the "true" earth ground. This phenomenon is more properly referred to as "stray voltage". [cite paper
author = Reinemann, Douglas J
title = What Do We Know About Stray Voltage?
publisher = University of Wisconsin—Madison
date = 28 March 2003
url =
format = PDF
accessdate = 2008-01-08

Finally, the term "stray voltage" is sometimes used to denote the controversial concept of high-voltage power lines causing injury to people and animals in the buildings nearby. This is a completely different topic from the "phantom voltage" discussed above.


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Voltage — Potential difference redirects here. For other uses, see Potential. Working on high voltage power lines, Pearl Harbor …   Wikipedia

  • Phantom power — (labeled as +48 V on some audio equipment) is a method that sends a DC electrical voltage through microphone cables. It is best known as a common power source for condenser microphones, though many active DI boxes also use it. Phantom power… …   Wikipedia

  • Phantom Power (disambiguation) — Phantom power refers to a method of sending DC electrical voltage through microphone cables. Phantom power refers to power consumed by any device while it is switched off.Phantom Power is also the name of three albums:* Phantom Power (Rick… …   Wikipedia

  • Phantom circuit — In telecommunication and electrical engineering, a phantom circuit is an electrical circuit derived from suitably arranged wires with one or more conductive paths being a circuit in itself and at the same time acting as one conductor of another… …   Wikipedia

  • Phantom Power — F/A/V A method of remotely powering the preamplifier or impedance converter which is buitlt into many microphones by sending a voltage along the audio cable. (Audio) PP A technology for powering microphones directly through the camera to save the …   Audio and video glossary

  • Steep Slope Sliders — Infobox VG| title = Steep Slope Sliders developer = Cave publisher = Sega designer = engine = released = 1996 genre = Sports modes = Single player, multiplayer ratings = platforms = Saturn media = requirements = input = Steep Slope Sliders is a… …   Wikipedia

  • Microphone — For the indie film, see Microphone (film). Microphones redirects here. For the indie band, see The Microphones. A …   Wikipedia

  • Список игр на Sony PlayStation Portable — Sony PlayStation Portable Ниже представлен список игр для консоли Sony PlayStation Portable. Обозначения игр, вышедших в разных регионах: NA  Северная Америка; …   Википедия

  • Ground (electricity) — In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth. A typical earthing… …   Wikipedia

  • List of Power Rangers in Space monsters — This guide covers the monsters that have appeared in Power Rangers in Space . To make a monster grow, on Astronema s command, laser beams called Sattelasers would be fired onto the monster to make them grow big.List of Monstersphinx Ship* First… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”