Stray Voltage

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wclark160

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Tennessee
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Electrical apprentice
Hello all. First thing first...I'm not an electrician, I'm an first year apprentice. My journeyman has tried and can't get to the bottom of the problem so...I have paid two licensed electricians ~ $1000 to come drive another ground rod and the problem still exist. I have slab foundation. My finished floors are stained concrete. When I'm standing on my floor barefoot and touch my fridge, stove, or any other electrical metal component, I feel it tingle.

Electrician #1 came out and determined that the wiring was sound in the house(new construction). Checked between the fridge and the floor (on a wet paper towel) and got 8 volts. He then started turning off breakers one at a time with not change. He then killed the main at the meter and it remained. He said it was a ground rod issue and drove another ground rod. It reduced the issue but it remained ~5V.

Electrician #2 came out and disagreed with #1 and said that its a slab bonding issue. He couldn't recommend anything (short of tearing out concrete) and pointed me to this forum for pointers.

So I ask, Any ideas?

Note: my slab has rebar but it is not tied to the electrical system/earth at all by a bonding wire. Elect#2 stated that though not required to bond the slab, it is always recommended.
 
If the electrician turned off the main, and you still felt current, the problem is obviously at the service. if the grounding and bonding are all good, I'd have the power company come out. Is you service fed underground? They may have an underground conductor problem.
 
The information give in your post strongly suggest a utility side neutral problem that could be on either the secondary side of the transformer, or, if the primary side is fed line to neutral, on the primary side.

Testing the line to neutral voltages with all loads off, and then with a large load on one leg, and once again with a large load on the other leg will tell you if the neutral issue is on the primary or secondary side of the transformer that supplies your house. Any substantial differences in these voltages points to a secondary neutral issue. If the voltages stay pretty much the same, that would point to a primary neutral issue.

Additional grounding electrodes will not fix this problem.
 
Additional bonding may _hide_ the problem, but won't fix it. Additional grounding electrodes may reduce the magnitude of the problem, by providing alternative paths for current flow to the soil, but they won't fix the problem.

If your slab is fully bonded to the neutral, in the fashion of a swimming pool, then everything will be at the same potential and you will not longer get a shock from your appliances to the floor.

However you might end up with shocks from the bonded structure (say an outdoor hose bib) to the surrounding soil.

The first electrician is correct; you are not required to bond slab rebar, unless it meets the requirements for a grounding electrode. But you are permitted to do so.

-Jon
 
Like the others had said, my mind immediately when to an issue with a utility company/service issue so give them a call. Although a potentially dangerous situation, this is a great learning example as an apprentice.

Just out of curiosity, if you take the cover off of your main panel, is the neutral bonded to the grounding electrode conductor? It may be possible that the bond is not there and equipment grounding conductors have been landed on the neutral terminal. if stray voltage travels back to the neutral, they could easily be transmitted through all of the EGC and equipment bonding jumpers creating a difference of potential between you and the concrete.
 
Could It possibly just be higher than average utility neutral to earth voltage?

I don’t know of there to be any spec to call it average or high but I typically think average would be 1-5volts NEV.
 
Rock86 said:
Like the others had said, my mind immediately when to an issue with a utility company/service issue so give them a call. Although a potentially dangerous situation, this is a great learning example as an apprentice.

Just out of curiosity, if you take the cover off of your main panel, is the neutral bonded to the grounding electrode conductor? It may be possible that the bond is not there and equipment grounding conductors have been landed on the neutral terminal. if stray voltage travels back to the neutral, they could easily be transmitted through all of the EGC and equipment bonding jumpers creating a difference of potential between you and the concrete.
Click to expand...
If this is neutral to earth voltage, the bonding would not make any difference. The connection to earth, or even multiple connections to earth do not make this issue go away, other than for a very small area of earth around the grounding electrode where the neutral voltage connected to the grounding electrode has raised the voltage of a small area of the earth.
 
Agree with others.
call the POCO and explain. If you have UG primary and it’s direct buried CN cable the neutral could be gone from corrosion if there is much age on the conductor.
We had this happen at a development. Kids getting 25-40 volts at a pool. Our N was gone. We ran a temporary neutral from the serving padmount to another padmount to fix the problem until we could replace the cable throughout the development.
 
Had similar issue in a pool with bonding all correct, probe in the water and another to remote earth, power off, and still had voltage present. POCO had pad mount xfer and underground conductors, in the underground hole corroded conductors were leaking current into earth and showing itself in the pool water. Once POCO made repairs no more voltage present in water.
 
Sounds like NEV if you get zapped when the main is off.
Mike Holt has a video that explains it.

Of course that doesn't mean there isn't also a neutral ground connection somewhere else creating a parallel path (objectional current)
 
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I'm asking the more experienced electricians here... I wonder, would a ground ring, exactly like a swimming pool ground ring around the house divert the NEV effects on people inside the house?

I know you can't get rid of NEV, but maybe a ground ring would bring everything inside the house to an equipotential state????

Also, another thought, isn't it possible that an electrical problem at a neighbor's house could cause this problem?
 
Sea Nile said:
I'm asking the more experienced electricians here... I wonder, would a ground ring, exactly like a swimming pool ground ring around the house divert the NEV effects on people inside the house?

I know you can't get rid of NEV, but maybe a ground ring would bring everything inside the house to an equipotential state????

Also, another thought, isn't it possible that an electrical problem at a neighbor's house could cause this problem?
Click to expand...
No diversion of NEV by adding grounding.
The EP bonding does not eliminate NEV, simply creates a state of a voltage gradient that allows for step potential to be within a safe level. Every grounding method whether it is rods, rings, pipe all have a gradient of dispersion horizontally and vertically around the grounding method. There have been tests that show this, for example if at the rod you have 120V, at 6 inches away you might have 100V, then move 1ft away and you might have 75V, and exponentially decreasing the farther away you get (values are only example not real). The EP bonding does kind of the same by creating a reduction of that gradient to the point is not felt to touch at a normal stride or reach.
A ring around the outside of building will be no different than rods, the gradient from the distance away from point of contacting the difference in voltage most likely would still exist as depth of basement floor also plays into the gradient.
You might be able to determine the direction of the NEV with a meter that can discriminate very low voltage difference by using the concept of gradient losses the farther from source you get. If test around perimeter of house basically finding voltages highest point and lowest point then draw a line through two point to form a pointer toward source. Could be POCO, your own underground, or neighbors house as prior suggestions made. You could likely do the same inside on concrete floor if your meter can discriminate low enough of voltage difference.
None of this would "fix" the issue but would give a direction to explore for a repair. Even if you can get it resolved it could come back with another source of NEV. Only real repair that might be more perminant regardless of source would be to create a full EP throughout the floor, but if source is strong enough even that would fail to eliminate it as step potential becomes shorter distance the higher the source value is.
Might be able to drive a couple of rods or put a ring specifically at the appliance creating a small EP location. But it won't eliminate the source of issue.
 
@Fred B: If that's the case, then the only remedy I can think of is putting a vinyl floor covering on the pretty stained concrete floor so the human body won't have a path to complete the circuit through the floor.
 
Rock86 said:
Like the others had said, my mind immediately when to an issue with a utility company/service issue so give them a call. Although a potentially dangerous situation, this is a great learning example as an apprentice.

Just out of curiosity, if you take the cover off of your main panel, is the neutral bonded to the grounding electrode conductor? It may be possible that the bond is not there and equipment grounding conductors have been landed on the neutral terminal. if stray voltage travels back to the neutral, they could easily be transmitted through all of the EGC and equipment bonding jumpers creating a difference of potential between you and the concrete.
Click to expand...
This is a 400 Amp service with 2, 200 amp disconnects outside. 1 200 amp disconnect feeds my house panel through a 4 wire feed. A ground bar was installed and the neutral bar and the ground bar are not bonded.
 
Thanks for the replies. The utility dept came out yesterday and checked their side of things. I was not home at the time but my wife was. She said they tested several things and then concluded that they "think" it is a ground rod issue. To my knowledge, they did not perform a ground rod resistance test, as their seemed to be alot of assumptions rather than facts. My electrician used a galv/tin coated rod where the utility dept recommended a copper. The rod was also very loose at the top so they are unsure of it's effectiveness. A copper rod will be installed today.
Thought...This monolithic slab has 2' wide, 4' deep footers that are in direct contact with the earth and should be at ground potential. If the ground rod was effective, it should also be at ground potential. Therefore, though not bonded together physically, the slab and the electrical system should be at the same potential.
 
wclark160 said:
Thought...This monolithic slab has 2' wide, 4' deep footers that are in direct contact with the earth and should be at ground potential. If the ground rod was effective, it should also be at ground potential. Therefore, though not bonded together physically, the slab and the electrical system should be at the same potential.
Click to expand...

This is a common misconception.

It would be true if the soil were a perfect conductor. But since soil has resistance different ground electrodes can be at different potential because of current flow in the soil. In other words the 'local' ground potential is not a fixed value and different ground electrodes sample different patches of earth.

The rebar in the footer you describe would likely qualify as a 'concrete encased electrode', and if so should probably have been connected to the grounding electrode system.

I like Fred B's suggestion of trying a few experiments to 'map' what is going on. Don't think of ground rods as magical '0V' devices. Think of them as antennas stuck into the soil. If you drive a short 'probe rod' (not a full ground rod; they are a pain to pull out again) and measure voltage between that probe and your existing ground rods, you should get a small voltage. Move the probe rod and you will likely get a different voltage.

-Jon
 
wclark160 said:
Thanks for the replies. The utility dept came out yesterday and checked their side of things. I was not home at the time but my wife was. She said they tested several things and then concluded that they "think" it is a ground rod issue. To my knowledge, they did not perform a ground rod resistance test, as their seemed to be alot of assumptions rather than facts. My electrician used a galv/tin coated rod where the utility dept recommended a copper. The rod was also very loose at the top so they are unsure of it's effectiveness. A copper rod will be installed today.
Thought...This monolithic slab has 2' wide, 4' deep footers that are in direct contact with the earth and should be at ground potential. If the ground rod was effective, it should also be at ground potential. Therefore, though not bonded together physically, the slab and the electrical system should be at the same potential.
Click to expand...
The connection to earth NEVER solves an electrical problem like this, or in general, never solves any electrical problem, however in some cases it can mask a problem to the extent that you may think it has solved the problem.
 
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