Hot ground wire (?)

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  #1  
Old 01-01-05, 08:41 AM
mrmac1
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Hot ground wire (?)

About a month ago I installed a ceiling fan where only a light had existed before. I had turned the electricity off at the switch and cut off the electricity at breaker box. I’ve got one of those little pen size current detectors, which showed no electricity coming into the ceiling box. I was pretty surprised when I got shocked in my left arm.
The other day I replaced the vent fan in my bathroom. Again electricity was turned off, but this time I did some judicious probing with a screwdriver. Unlike the ceiling fan, the vent fan is at the end of the run and thus has only one wire coming into it (w/ hot, neutral, and ground wires inside). The screwdriver probe flipped the GFCI. (The bathroom and the ceiling fan room are on different circuits.)
When I told a guy I know about all of this, he said that I had a hot ground wire. This made perfect sense, but I can’t figure how that could have happened. The receptacle tester doesn’t show any problem nor does the circuit detector (the little pen) indicate that the ground at the receptacle is hot.

My plan:
I’ll test the ground with a multimeter. This should indicate a hot ground wire – but not the full 110 V.
I’ll turn off breakers, each time checking to see if the ground wire continues to be “hot.”
When I’ve located the faulty circuit, I’ll track down the failing connection, starting at the breaker box and continuing outward away from the box.
Locate and correct problem.

Does this make any sense?

Thanks for your help - Dick
 
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  #2  
Old 01-01-05, 08:50 AM
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Because of phantom voltage, testing wires with a digital multimeter is very often misleading. You're better off with a simple $2 neon circuit tester or a $15 non-contact tick tester.

A hot ground wire is theoretically impossible. A hot bare wire or a hot green wire is possible, but very, very rare.
 
  #3  
Old 01-01-05, 09:35 AM
mrmac1
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The multimeter is analog - will that make a difference? Will the tick tester measure voltage below 110V?

I need a lesson on wiring terminology – I thought that the bare wire was the ground wire – [black – hot, white – neutral].

Do you have any recommendations as to how I should proceed?

Thanks,
Dick
 
  #4  
Old 01-01-05, 10:06 AM
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A black wire is just a black wire.
A white wire is just a white wire.
A bare wire is just a bare wire.

The above terms are physical descriptions of the wire.

A hot wire has a voltage potential relative to ground.
A neutral wire has little or no voltage potential relative to ground.
A grounding wire has zero voltage potential relative to ground.

The above terms describe a wire's function.

It is important not to confuse the physical description with the functional description. This is because:
  • Not all hot wires are black.
  • Not all white wires are neutral.
  • Not all neutrals are white.
And that's just if things are wired correctly. If things are wired incorrectly, then anything is possible.

An analog voltmeter is much less subject to phantom voltage than a digital voltmeter.

Encountering voltages between 0 and 120 in a house is rare.

If you are well versed in electrical theory, proceed with your plan. Otherwise, read several good books before diving in. If you start testing without enough knowledge, you will get quickly confused and, heaven forbid, may misguidedly change something that is currently correct and safe to something that is wrong and dangerous.
 
  #5  
Old 01-01-05, 11:41 AM
mrmac1
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So if a bare wire (which had been intended to be the ground) were hot, it is by definition NOT the ground?

I tested a few receptacles – all with the same results – this is from the GFCI through which power runs to the vent fan. This seems to substantiate the results of the plug-in tester and the tick tester.

hot to neutral -> current
hot to ground -> current
neutral to ground -> nothing

If the bare wire were hot in one place, shouldn’t it be hot throughout the house – or asked another way, aren’t all of the bare wires supposed to be linked?

I had expected (before your last message) to find some current passing between neutral and ground. Without that I’m back to square one – have you covered phantom current in another place? Or do you have a book or article that you can recommend?

Thanks,
Dick
 
  #6  
Old 01-01-05, 12:50 PM
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A bare wire is never SUPPOSED to be hot. But something is wrong in your case. The bare wire is supposed to be continuous from any and all locations back to the ground terminal at the main box. As long as this condition is satisfied, then IF a defect arises which places voltage on the bare wire then
(a) the wire should still be at zero potential and thus not shock you , and
(b) the short circuit from hot to ground should cause a circuit breaker to trip.


I think the first thing I might investigate is continuity of your bare wires from any and all points to panel ground. You could do this by turnin off your main breaker.....turn off all power to the house. Then test using your multimeter and some long pieces of any wire as an extended test lead. Fix any faults found here and then investigate possible shorts or opens in the neutral circuit.
 
  #7  
Old 01-01-05, 01:41 PM
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May be this will help.

To get zapped your body must complete a circuit.

Example: BUT do not try this.(Very Dangerous,it can kill)
one hand is holding a hot wire, say black.
Your other hand touches a ground, you get zapped.
The ground is not HOT. your HOT, holding a HOT wire.

What hot wire/thing were you holding when you got zapped.
 
  #8  
Old 01-01-05, 02:45 PM
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hot to neutral -> current
hot to ground -> current
neutral to ground -> nothing
This is the way it supposed to be.

By the way, you are not measuring "current" but "voltage".

If the bare wire were hot in one place, shouldn’t it be hot throughout the house – or asked another way, aren’t all of the bare wires supposed to be linked?
If all the bare wires are linked, and linked to the power company neutral and to your grounding rod, they cannot be hot. The only way a bare wire can possibly be hot is if it isn't linked, or if the power company neutral is disconnected.
 
  #9  
Old 01-01-05, 06:05 PM
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The reason you tripped the GFCI is you shorted the white to ground. This created an imbalance in the current between the black and the white. The GFCI worked properly.
 
  #10  
Old 01-01-05, 08:14 PM
Savant
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Originally Posted by John Nelson
If all the bare wires are linked, and linked to the power company neutral and to your grounding rod, they cannot be hot. The only way a bare wire can possibly be hot is if it isn't linked, or if the power company neutral is disconnected.
I'm thinking the service panel ground might be bad. (IE, no or bad connection to cold water pipe and/or ground rod) Since there is usually a low level current flow on the ground, (perhaps up to 20-25% of the return current) then it's possible that the return current is 'presenting itself' on the ground wires and providing a path to ground when touched by the poster in question. While I would expect that the neutral return would pick up the slack should the panel ground go bad, that wouldn't eliminate the potential on the ground line if there was no ground present.

Considering the shape I have seen some ground wires in (for old houses) they can often lose effectiveness for numerous reasons. My thought here would be to check the panel ground and trace it to the point where it should be connected at both ends, and see if there is anything obviously wrong.

Regards,

Savant
 
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