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simonb 09-06-2007 09:20 PM

IS this right?
 
Stumbled upon another little problem that im not sure if it should be this way.

I have a double wall switch fed by 14-2. From that point they feed 2 lights close by using a 14-3. The red 120 for one light and the black 120 for another, using white for neutral. I notice when i turn one of the lights on, lets say the one using the red wire, the black wire gets energized. Now i know this is induced voltage, but what when both lights are on, is this safe, should this be used this way?

jbfan 09-06-2007 09:29 PM

It is normal and done all the time.

sluggermike 09-07-2007 12:29 AM

It sounds like the "old phantom voltage" again. Little did I know when I posted the question about what I thought was feed back voltage that so many people were also wondering what was happening when they noticed that they were getting a reading on a digital voltmeter when checking the circuit that was off when using 12/3 or 14/3 romex. My son who is a computer whiz explained it to me in another way. He referred to like "cross talk". Thanks again for all your help.

joed 09-07-2007 03:50 PM

Your using a digital meter. Common problem of false/phantom voltage.

BigJimmy 09-08-2007 12:34 PM

Quote:

Originally Posted by joed (Post 61811)
Your using a digital meter. Common problem of false/phantom voltage.

I cannot agree more. I work in railroad signaling for an electrified mass transit agency. The majority of the system is based on the use of low voltage, DC circuits many of which extend from one location to another over aerial lines. I have seen countless young maintainers with their brand new Fluke 87's wonder why a relay won't pick (energize) with what appearts to be rated voltage across its coil. Flukes are great liars (although I'm not singling them out; all high-impedance DVM's will perform the same). Now, when you show them what happens when you place a test light (a load) over the coil and, huh?? No light?? (some have exclaimed at this point, "This piece of sh** [Fluke] doesn't work! I'm taking it back!").

Whether you call it phantom voltage, induced voltage, crosstalk, etc. it is certainly one of the most important concepts for any elecrical professional to understand.

TTFN

frenchelectrican 09-08-2007 01:47 PM

Unforetally ,,

this is true with digtal volt/ohm meter they will pick up " ghost or pathom voltage" this is very common with it.

That why most good electricians will carry at least 2 or more voltmeters one DVM and one anlong type [ which it can put a load on ] to read the votlage and the other tester i used pretty often is "wiggy®" that will put a load on the line pretty good to elamated the ghost voltage or inducted voltage on the line.

if i dont have those on hand what i do is get 240 volt bulb and get a pigtail socket and test this as well that will put on the load to verify it as go or no go voltage test very simple test

Merci, Marc

joed 09-09-2007 08:28 PM

Quote:

Originally Posted by BigJimmy (Post 61909)
I have seen countless young maintainers with their brand new Fluke 87's wonder why a relay won't pick (energize) with what appearts to be rated voltage across its coil. TTFN

That seems odd. Can you explain to me why the coil does not apply enough load to make the voltage read properly. Phantom voltage is usually a problem on open circuits.

elkangorito 09-10-2007 09:44 AM

Quote:

Originally Posted by joed (Post 62115)
That seems odd. Can you explain to me why the coil does not apply enough load to make the voltage read properly. Phantom voltage is usually a problem on open circuits.

I've got to agree here. Did the maintainer disconnect the relay & then measure the open circuit voltage?


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