voltage on egc

[jernst]

I was replacing a receptacle in an older house, the power was off for that circuit, I got a tingle when i touched the ground wire so I checked it with my meter and found the ground wire has 50 volts on it. I seperated all the wires from each other, traced it back to the other end of the wire and it had only 1.5 volts on it at the other end. I also checked the receptacle that was a few feet from it and on a different circuit and that ground wire has 7 volts on it. I cant seem to figure out the problem. If anyone could give me information on this that would be great.
Thank You,
-Jack

 

[tom baker]

What type of meter?
Analog or digital?

 

[Smart $]

Generally the ground wire is the reference for voltage and voltage drop measurements of Line-to-Neutral branch circuits.

Since you need two test points to measure a voltage differential, what was the other test point used in each of your measurements?

 

[mcclary's electrical]

Reference you're meter back to the panel when doing this. Stretch thhn accross the floor wil work fine. It sounds like somewhere,,,theere is a neutral bonded to the EGC. It could be in some cord and plug connected equipment. Probably in the wiring

 

[brian john]

Some are as noted above.
1. What type of meter were you using?
2. What were you referencing it too?
3. There will often be a difference of potential between the ECG and grounded conductor depending on load on the circuit and distance from the panel.
4. Was this a multi-wire branch circuit?
5. Do you have current on your neutral ground bond?
6. Do you have current on the GEC?
7. Not trying to be funny are you sure it was not a muscle twinge.
8. Will it light a 12 volt lamp?

 

[jernst]

It was a digital meter, with the power off I seperated all the wires and with the one egc that had the 50 volts on it I measured between that and all of the other dead wires and got the 50 volts each time.

 

[brian john]

Use a wiggy and a incadescent lamp on 5 volts use 4 12 volts lamps in series. and READ THIS

From NEMA

Phantom Voltages

This Bulletin is intended to address the occurrence of so-called “phantom” voltages, a phenomenon detected during the testing electrical conductors in the field.

Due to the high impedance of measuring instruments, a voltage reading may be detected on open conductors where there is no hard electrical connection to a voltage source. Conductors that are installed in close proximity to one another, and are capacitively coupled to each other, can cause this a.c. voltage reading. Such a reading could be 2 or 3 volts, or it may be as high as the voltage on the adjacent conductors. This is what is referred to as a “phantom” voltage.

According to Underwriters Laboratories Inc., this can be a harmless reading and can be caused by the high input impedance of the measuring instrument, which places very little loading on the circuit under test. The capacitance is increased as the length of the run is increased. A 50-foot run may produce a pronounced capacitance effect whereas a one-foot sample may not produce any. This effect has such high impedance that, although a voltage can be detected, there is little or no available current.

Since the “phantom” voltage is a physical phenomenon involving very small values of capacitance, it cannot energize a load or cause physiological damage to a person.

Care must be taken to be sure that the voltage reading is a phantom voltage, which is caused by improper use of high impedance multimeters, and not as a result of a cable defect or improper installation, which may result in a shock hazard.

In order to help minimize the likelihood of reaching a wrong conclusion from this phenomenon, NEMA recommends the use of a UL Listed or OSHA-approved low impedance multimeter in place of a high impedance multimeter or other high impedance measuring device for testing on open conductors where there is no hard electrical connection. Without a low impedance measuring device, a high voltage reading is an inconclusive indication of possible faults in the cable.

Distribution List:
Standards and Conformity Assessment Policy Committee
Codes and Standards Committee
NEMA Executive Staff

 

[Smart $]

It was a digital meter, with the power off I seperated all the wires and with the one egc that had the 50 volts on it I measured between that and all of the other dead wires and got the 50 volts each time.

In order to eliminate phantom voltage on the receptacle in question, simply plug in a working lamp and leave it turned on when you turn the power off. Measure voltages between the current-carrying conductors and the EGC with power both on and off. Change in readings may clue you in on the problem.

If there exists more than a few volts between conductors with the power off, first thing to check for is whether this circuit is part of a multiwire branch circuit (MWBC). You could be reading the voltage drop of the other energized and conducting circuits current through the shared neutral conductor, but the reading still should not be more than a few volts... but verifying the existance of a MWBC could explain more than the few volts, and turning the power off to the other branch should reflect a lower measured voltage. Either being part of a MWBC or not reading more than a few volts likely indicates a degraded neutral connection somewhere in the circuitry wiring, somewhere from the test point to and including connection at the panel.

Remeber that when you measure voltage, there is no way to tell from those two test points which one is energized and which is not (though a non-contact tester may, if it can indicate the presence of substantially less than full line voltage).

Another way is to use an alternate known good source as additional test points, such as the receptacle a few feet away—which seems to be operating within normal parameters. Check neutral to neutral, (2X) neutral to ground, and ground to ground voltages between the two receptacles. This will help you to determine which conductor is exhibiting a fault condition.

Once you determine which wire has the problem, you just have to explore and find the culprit condition

 

[76nemo]

Alot of you guys refer to using a "wiggy". Have you not concidered a dual impedance meter? Shoot, for a $130, why not?????

 

[brian john]

Alot of you guys refer to using a "wiggy". Have you not concidered a dual impedance meter? Shoot, for a $130, why not?????

I have one my post are to assist the guy asking the question that may not have a clue what he is seeing.

 

[jernst]

the receptacle in question has the bottom portion switched, and the egc that seems to be the problem is the one running from the switch, might that have anything to do with it?

 

[brian john]

the receptacle in question has the bottom portion switched, and the egc that seems to be the problem is the one running from the switch, might that have anything to do with it?

AHHHHH The little things we leave out of our post YESSSSSSSSSSSSSSSS!

 

[jernst]

So does that mean the switch must be removed?

 

[wptski]

Is this similiar to this thread about phantom voltage where half of a duplex is switched? It was a very good thread by the way!

 

[JohnJ0906]

Some are as noted above.
1. What type of meter were you using?
2. What were you referencing it too?
3. There will often be a difference of potential between the ECG and grounded conductor depending on load on the circuit and distance from the panel.
4. Was this a multi-wire branch circuit?
5. Do you have current on your neutral ground bond?
6. Do you have current on the GEC?
7. Not trying to be funny are you sure it was not a muscle twinge.
8. Will it light a 12 volt lamp?

I have gotten a muscle twinge while working, and I thought it was a shock at first.

 

[LarryFine]

I have gotten a muscle twinge while working, and I thought it was a shock at first.

I get that once in a while. :roll:

"Gasp! A shock!"

From a plastic box with no wires in it? :-?

Fortunately, people rarely see me jump like that.

 

[electricalperson]

did you check neutral to ground? or did you measure hot to ground and had 50v? if you measure hot to ground and have 50v and 120v line to neutral you have a loose ground. if you measure from neutral to ground and have voltage somethings loose. but if you measure the switched conductor that doesnt have power on it in a 14/3 cable you can get phantom voltage if there is live wires in that cable

 

[brian john]

I have gotten a muscle twinge while working, and I thought it was a shock at first.

I have almost soiled myself from this.

 

[ptonsparky]

Thought I had a muscle twinge once, until I touched the box again. I now carry testers that glow or hum.

 

[LarryFine]

Thought I had a muscle twinge once, until I touched the box again.

You thought you were wrong, but you were mistaken!