Talk:Phantom voltage

Justification: The topic of phantom voltage comes up frequently in web discussion groups. People working on electrical stuff measure the voltage on a disconnected wire and are confused because they get a reading. Some web reference is needed to point them to to explain this.

I'm actively seeking some better references.

drh 15:11, 24 January 2007 (UTC)

Agreed. Especially the confusion with `phantom power` in professional audio. These two concepts crop up all the time. Perhaps tagging this article with the proper electronics category would gain it some more exposure, and hence a contributor to clean it up. 65.112.197.16 21:32, 17 July 2007 (UTC)

Undo
I manually undid the changes by woodturner9, and in the process probably lost some other edits. There's no scientific basis for attributing ordinary phantom voltage in electrical power wiring to inductive coupling.

Inductive coupling IS a factor in signal wiring, but that's a different topic. If someone wishes to start a page on that topic and link it to this one that's fine.drh (talk) 12:31, 5 December 2007 (UTC)

Response
To the contrary, inductive coupling is the PRIMARY source of so called "phantom voltage" at low (AC line) frequencies. It's factually incorrect to refer to this as capacitive coupling. Engineers have been fighting this misinterpretation for decades, and we shouldn't be adding to the misunderstanding. There simply is not enough capacitive coupling at frequencies less than 1 KHz or so for any significant capacitive coupling to occur.

The page as changed refers to capacitance of a cable, citing numbers for NM-B cable. However, this is the capacitance per unit length, which has nothing to due with the capacitave coupling between two conductors.

Perhaps the best resolution of this dispute is to find some real, definitive references, rather than relying on web pages that may perpetuate the misinformation. I'll see what I can find. Woodturner9 (talk) 11:34, 6 December 2007 (UTC)

Inductive coupling would only occur if there were current flowing, and there is none to speak of in the most common phantom voltage scenarios. Either it's capacitive coupling or magic, and my EE degree says capacitive coupling.24.159.203.105 (talk) 19:36, 13 January 2008 (UTC)

By that logic, it couldn't be capacitive coupling either, since both would require current flow. In fact, there is and must be current flow for both capacitive and inductive coupling. There HAS to be current flow for the meter to register ANYTHING, it's just a small current.

If your EE degree says it's capactive coupling, I'd stop listening to your EE degree :-) I have taught these subjects at university for many years (my BS, MS, and PhD are in EE), and it is clearly inductive coupling.  I probably should add some of the textbook references, so folks can look it up if they want to learn more.  —Preceding unsigned comment added by Decolores9 (talk • contribs) 20:55, 21 February 2008 (UTC)

For the inductive scenario there has to be a load on one circuit, but with the capacitance scenario there does not. It is worth mentioning that you can buy low impedance meter designed to not measure phantom voltages. Also, the impedance of those outlet testers with the 3 lights is remarkably high. I have one that claims 0.3 watts but measures over 20 mega-ohms on two good multimeters. I assume it uses neon lights. I imagine that inductive coupling might give a small voltage with rather low impedance, whereas the classic phantom voltage is a big voltage with high impedance (disappears when you try to draw current, unless it's using a 3 light tester, and even that will appear dim). Physicsjock (talk) 18:31, 6 February 2009 (UTC)

Current flow (or "a load") is required to induce voltage either inductively or capacitively. Low impedance meters require greater current flow to measure the voltage, and this higher current flow discharges the field of the inductor (or capacitor) to dissipate the phantom voltage. Both inductive and capacitive coupling induce relatively large voltage with high impedance. Woodturner9 (talk) 16:47, 28 September 2010 (UTC)

Suggest merge
I suggest this article should be merged to Stray voltage which discusses these phenomena at length. --Wtshymanski (talk) 18:38, 9 September 2010 (UTC)

Stray voltage as discussed in that page is a different phenomena. I don't think the pages should be merged. Woodturner9 (talk) 16:44, 28 September 2010 (UTC)