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#56911 - 10/02/05 08:14 PM Brown voltages on a 12-3
danickstr Offline
Junior Member
Registered: 10/01/05
Posts: 9
Loc: seattle wa
Hey guys I got 45 volts and 18 volts on my two legs, and 119 on the other. I figure there is a drywall screw through them, but anyone have any tips on finding the location??? thanks. Nick EC in Seattle
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#56912 - 10/03/05 01:31 PM Re: Brown voltages on a 12-3
CTwireman Offline
Member
Registered: 02/07/02
Posts: 840
Loc: Connecticut, USA
With readings that precise, I am guessing you are using a digital meter. What you are reading are mostly like ghost voltages and can be ignored.

Do yourself a favor and use a solenoidal (wiggy) tester for basic voltage checks. If you check this again with a wiggy, more than likely you will not read any voltage.

If you indeed have a drywall screw through a wire (which I doubt), you could derermine it a continuity check.

Peter
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#56913 - 10/03/05 01:33 PM Re: Brown voltages on a 12-3
CTwireman Offline
Member
Registered: 02/07/02
Posts: 840
Loc: Connecticut, USA
I just read your profile and you don't list any occupation. I'm afraid what I've told you may mean nothing if you're not in the electrical trade. Remember, we can't help you with a DIY project.
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#56914 - 10/08/05 10:02 AM Re: Brown voltages on a 12-3
danickstr Offline
Junior Member
Registered: 10/01/05
Posts: 9
Loc: seattle wa
thanks for info. I am indeed a licensed EC in Washington. will try a wiggy.
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#56915 - 10/08/05 10:53 AM Re: Brown voltages on a 12-3
danickstr Offline
Junior Member
Registered: 10/01/05
Posts: 9
Loc: seattle wa
it was ghost voltage. I had my Fluke 112 stolen and was using a radio shack MT. It goes to show what a good tool does for us that we forget. thanks again Peter!
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#56916 - 10/08/05 02:42 PM Re: Brown voltages on a 12-3
CTwireman Offline
Member
Registered: 02/07/02
Posts: 840
Loc: Connecticut, USA
You're welcome Eric.

By the way, the ghost voltages are caused by capacitance coupling, in case you were wondering. I understand the idea but I'm not too good at explaining it. Hopefully someone else can jump in and explain it.

Peter
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#56917 - 10/08/05 05:23 PM Re: Brown voltages on a 12-3
danickstr Offline
Junior Member
Registered: 10/01/05
Posts: 9
Loc: seattle wa
that would be great. I am always anxious to understand the physics behind such phenomena.
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#56918 - 10/08/05 05:43 PM Re: Brown voltages on a 12-3
CTwireman Offline
Member
Registered: 02/07/02
Posts: 840
Loc: Connecticut, USA
I'm going to try at any rate. First of all, a capacitor is simply 2 plates separated by an insulator.

Well, consider a piece of 2 conductor cable. What do we have? 2 charged bodies separated by an insulator - a capacitor! It should be noted that wire has extrememly small amounts of capacitance (and inductance too) at 60 hertz.

Now, the story changes entirely when we talk about high frequencies. A short piece of wire can turn into an open circuit at high frequncies due to capacitance, but that's a whole 'nother story. Let's just say I wouldn't want to be in integrated circuit design right now.

So, in the case of this 12/3 with one of the two hots deenergized, the live conductor actually induces a voltage on the other dead conductor due to capacitance. This is where I get lost in the physics of it all, so hopefully someone else can jump in.

Peter
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#56919 - 10/09/05 08:52 AM Re: Brown voltages on a 12-3
e57 Offline
Member
Registered: 05/27/03
Posts: 2876
Loc: S.F.,CA USA
More electro-magnetic induction than capacitance. IMO Think of it as a elongated transformer. It is a voltage, not usable, but not a ghost... The voltage is real on the open conductor, but if you load it with say, a Wiggy, seeing that there is no "Umph" to it, it drops out. If you grounded one side, it would be a lower voltage like ~.05-.5 on the other side. Both sides, and you shouldn't get anything...

Disclaimer: One should be very carefull of grounding unknown circuits of unknown voltages or partial nominal voltage! It may also be a resistive connection on real, and usable voltage, and result in a short.
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#56920 - 10/09/05 09:41 AM Re: Brown voltages on a 12-3
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9039
Loc: Estero,Fl,usa
I think a digital meter, aimed at the electrical trade, should have a scale that parallels a ~100k resistor across the leads, for checking voltages.
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