Stray voltage on ground wire in townhouse

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WestCascadesElec

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Vancouver, Canada
My accountant called me to help troubleshoot a issue he is having at his townhouse. Here is what happened so far, coax cable burnt clean off of his receiver box at the main tv and in the master bedroom the ground wire in tv power supply cord heated up only on the ground wire and melted it a little bit. So now there is a spiral all along the cord from plug to tv. His range was off and randomly started smoking so it was shut off at the breaker. I come over to try and start looking into this, what I have found so far is there is a voltage difference of approx 10-12 volts between ground and neutral at every receptacle and also on the panel mains. Between a grounded outlet and coax ground in a room there is the same voltage difference. I go to the garage and open the panel and also the tel/cable supply panel, disconnect all coax lines running up the rooms and measure them, 0 volts difference. I measure the coax line leaving the townhouse to the main ground in the panel and same voltage difference of 10-12 volts. I've never encountered this before but only heard of guys trying to troubleshoot it. Where would be the best place to begin looking at it?
Thanks for any insight

Forgot to mention, tightened all neutral and ground connections in the panel. Some were quite loose
 
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170831-0612 EDT

WestCascadesElec:

In your main panel the EGC bus bar (what I believe you are calling ground) must be bonded (very low resistance connection) to the neutral bus bar. Thus, within the main panel the voltage difference between the EGC bus bar and the neutral bus bar must be very low (millivolts). If not, then fix this bond. Usually the bond is via screws from said bus bars to the main panel enclosure.

If the voltage between said bus bars is low, then create a long test lead (an extension cord can be used). Connect this test lead to the EGC bus bar. Go to an outlet where you saw a difference between EGC and neutral, and relative to the test lead measure the voltage between the test lead and the outlet EGC, and the test lead and the neutral. This will tell you which path has an open somewhere.

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I agree with the crowd here. You are looking for an open neutral _somewhere_ combined with a neutral-ground connection somewhere else.

Neutral current is trying to get back to the transformer, and is using the egc and grounded cable shield as the path.

The fault _may_ be in another house. A neighbor's open neutral could put current on shared grounded metal, eg the cable tv system.

The fault may involve bootleg grounds or ground to neutral connections in branch circuits.

You may need to add a galvanic isolator to the incoming cable to break the ground path.

-Jon
 
Not only is there an open neutral issue someplace (as mentioned may even be at a neighbors's house) but seems to be no bond between neutral and EGC at the service either.
 
170831-0923 EDT

Within my Sq-D main panel there appear to be two substantial cross members (bars) between the EGC bus bar and the neutral bus bar. Their total cross sectional area may be as large as one of the hot bus bars.

I don't know my present neutral current, but the voltage drop between the EGC and neutral bus bars is prrsently 0.3 millivolts. Some of this voltage may be inductive coupling to my one tutrn loop formed by the meter test leads.

.
 
gar said:
170831-0923 EDT

Within my Sq-D main panel there appear to be two substantial cross members (bars) between the EGC bus bar and the neutral bus bar. Their total cross sectional area may be as large as one of the hot bus bars.

I don't know my present neutral current, but the voltage drop between the EGC and neutral bus bars is prrsently 0.3 millivolts. Some of this voltage may be inductive coupling to my one tutrn loop formed by the meter test leads.

.
Click to expand...
With Square D loadcenters made for the past 25 or so years, that cross member is considered a part of the neutral assembly and both terminal bars are considered neutral buses. They aren't even designed to be easily separated to make one a neutral and one a EGC bus - the intent for a separate EGC is to add a separate bar that is bolted to select position(s) on the cabinet itself.
 
170831-1329 EDT

kwired:

On my 52 year old QO main panel it is truely one neutral bus used for both neuttal and EGC. Of the three actual neutral bars there is no way to separate one from the group.

There is no obvious designed place for a separate EGC bus.

.
 
gar said:
170831-1329 EDT

kwired:

On my 52 year old QO main panel it is truely one neutral bus used for both neuttal and EGC. Of the three actual neutral bars there is no way to separate one from the group.

There is no obvious designed place for a separate EGC bus.

.
Click to expand...
That type of panel is often referred to as SOSE (Suitable ONLY for use as Service Equipment) as different from SUSE (Suitable for Use as Service Equipment.)

If you needed to use it as a sub panel for any reason you would have to add one or more insulated neutral bars, possibly creating a configuration that was not UL Listed.
 
Thanks for all the responses, I will be starting this next week as its just so busy right now. For the previous response saying that the neutral and ground should be connected that is not allowed up here in our cec. Bonding screw has to be removed on this panel as it is considered a sub panel since there is a main meter stack in the electrical room for each bank of townhouses. I believe its called division of currents which van cause a ground loop.
 
WestCascadesElec said:
Thanks for all the responses, I will be starting this next week as its just so busy right now. For the previous response saying that the neutral and ground should be connected that is not allowed up here in our cec. Bonding screw has to be removed on this panel as it is considered a sub panel since there is a main meter stack in the electrical room for each bank of townhouses. I believe its called division of currents which van cause a ground loop.
Click to expand...

The proper term is objectionable current over the EGC wires (which are in parallel with that section of neutral and so will end up carrying normal current) rather than ground loop.
One way a true ground loop can occur is where two or more EGCs are connected at equipment end (or anywhere but the panel bus) forming a loop in which magnetic fields can induce unwanted currents, which in turn can cause voltage offsets.
 
170831-1640 EDT

WestCascadesElec:

At your main panel measure the voltage between between neutral and EGC.

From your other information it is quite probable that this will be large, like a moderate percentage of your 10 to 12 V.

Go find where neutral and EGC are bonded together. Use this as the reference point for your long test lead. Relative to this said reference point measure the voltage drop to neutral at the main panel, and to the EGC at the main. With these voltage drops known they should lead us to where the principle problem is located.

.
 
Currently working on this today. What has happened so far, shut off main and no more stray voltage. Measured neutral to ground and began turning on breakers one by one. Voltage slowly starts creeping up from 0.5v to the 8.1v by the time all breakers are turned on. Is there any possibility that this could just be induced voltage. We are currently opening up boxes and looking for anything out of the ordinary one circuit at a time
 
WestCascadesElec said:
Currently working on this today. What has happened so far, shut off main and no more stray voltage. Measured neutral to ground and began turning on breakers one by one. Voltage slowly starts creeping up from 0.5v to the 8.1v by the time all breakers are turned on. Is there any possibility that this could just be induced voltage. We are currently opening up boxes and looking for anything out of the ordinary one circuit at a time
Click to expand...

The neutral and ground (GES/GEC/EGC) are supposed to be metallically bonded. There is no way that you could get a voltage of 8.1 volts with a solid metallic connection.

More likely is that the two wiring meshes are not in fact bonded together AND you have a high resistance neutral somewhere which is causing the neutral to get farther and farther from ground the more unbalanced current it is carrying.

The only way you might possibly be seeing induced (phantom) voltage on the EGC is if it is not in fact connected to either the neutral or the ground electrodes.
 
To get a better understanding of the neutral situation I would start with turning off the main breaker and carefully remove the service neutral and the from terminal and the grounding electrode conductor and isolate both of them.
Then see what you get for voltages between the hot legs, hot to neutral, and neutral to the EGC.
 
Where does ground and neutral merge in Canada?

Turn off every single breaker and disconnect the coax that's getting hot.

I prefer keyless lamp sockets with built-in recep setup as MWBC (or N, L1, L2 and L3 if you work 208Y/120 often). You connect neutral to neutral, one socket to L1, the other socket to L2 and fit incandescent in both. Find empty breakers or vacate them and energize just these two sockets.

Plug something into the side socket that draws a few amps. A loose neutral make the loaded one dim and the other one brighten. After you check the feeder neutral connection from feeder to panel is good you've ruled it out as problem before his panel. This is a utility problem now. No need to open every box at this point.

An isolated 1-2kVA 240 to 120 (not auto transformer) can be used to provide power for refrigerator from L-L until utility can come by but everything else should be left off to avoid damage.

The entire length of coax going back to the bonding point, as well as the Romex that supplied current to the branch connected to TV may need to be replaced if you see signs of heat damage.
 
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Ground and neutral are connected at the main panel coming from the meter base. For the townhouse I am working on the ground and neutral are connected in the electrical room for the bank of townhomes being served. All panels downstream must have the bonding screw removed from the neutral bar to the panel frame. Didn't find anything today, will be working on Saturday to hopefully find this. Plan to disconnect everything in the panel and test each incoming wire individually to try and pinpoint what circuit and hopefully find which area of the house is the cause
 
If neutral and ground are bonded together, you shouldn't have anything between them, if close to the bonding point.

As you get further away from that bonding point, the chance of measuring voltage between them increases because of voltage drop on the neutral (it will have voltage drop if there is current flowin in it)

Voltage to the coax cable - you need to figure out which is closer to true ground the cable or the power system grounding. You could have current trying to come into the premises via the coax cable rather then having premises power system leaking to the coax, meaning the problem may be coming from outside the premises.
 
170913-2431 EDT

WestCascadesElec:

Did you pay any attention to what I wrote in post #13, and/or did you not understand what I said?

Go find the point where neutral and EGC are supposed to be bonded together. Measure the voltage between the actual wires (neutral and EGC) (this means put your meter probes directly on the wires and not the terminals. or lugs). This voltage should be quite close to zero, obviously with no load it should be zero, but even with a full totally unbalanced load the reading should be close to zero.

If this bond is good, then use this bonded location as the voltage reference to your meter to investigate were the large voltage drop is occurring. Don't worry about the bonded point to earth at this time. If there is a problem relative to earth solve that later. At this time don't use some earthed point as a reference, just use the bonded location.

.
 
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