NEV voltage and pool bonding

[Becker Electric]

When checking the NEV of a pool perimeter, how much variance of Nev is ok between my reading at the service supply panel and the pool permiter. ( for example if Nev at main panel is reading .24 volts and the NEV is reading is different at perimeter lets say .38 volts at the pool perimeter is that too much variance and is a good indicator the permiter is not bonded? Essentially what variance is Ok to allow to confirm bonding.

 

[W@ttson]

When checking the NEV of a pool perimeter, how much variance of Nev is ok between my reading at the service supply panel and the pool permiter. ( for example if Nev at main panel is reading .24 volts and the NEV is reading is different at perimeter lets say .38 volts at the pool perimeter is that too much variance and is a good indicator the permiter is not bonded? Essentially what variance is Ok to allow to confirm bonding.

So this reminds me kind of when Faraday did his experiments to prove that magnetism and electricity were connected. He had a coil and a magnet. He then moved the magnet through the coil and went to the other room to see if he can measure the result. By the time he got to the other room he could not see any effect. The effect can only be witnessed during the motion of moving the magnet in and out through the coil.

It could be very much the case that you measured at the service entrance and got X NEV, then by the time you walked to the pool perimeter you measured Y NEV because loads in the neighborhood changed.

NEV is ever changing and determined by loads outside of the premises. You can have your main breaker off at the house and still have a NEV.

 

[don_resqcapt19]

In my opinion there should be no variance, but that assumes no system load changes between the time you read the voltage at the supply and the time you read it at the pool.
There is no standard as to what may be acceptable.
I would look at doing it with two meters at the same time. One connected to between the service GEC and the remote electrode, and the other connected between the pool equipment and the remote electrode. Readings taken at the same time should be within a few hundreds of a volt of each other, assuming your meter has that good of resolution.

 

[Rjryan]

www.mikeholt.com/pools
There is a PDF that accompanies the video
In that video Mike shows that the Neutral-to Earth Voltage changes with the feeding transformer load.
In the video he shows that it does vary and there is no standard for what is acceptable or normal.

 

[Rjryan]

From a Common origin point the Neutral-to Earth Voltage should be very close at all points of the pool and no voltage reading between the bonded points of the pool to each other.

 

[W@ttson]

www.mikeholt.com/pools
There is a PDF that accompanies the video
In that video Mike shows that the Neutral-to Earth Voltage changes with the feeding transformer load.
In the video he shows that it does vary and there is no standard for what is acceptable or normal.

OH MY!!!! I have been looking for that video for SOOOOO LONG. I watched it a while ago and then went to look at it again but it went private. Thank you for finding it!

 

[Rjryan]

You are welcome, it is a real tribute to Mike Holt to put out this caliber of information and show in actual practical testing of a pool.
I have not seen anything close to the scope of the information Mike gives in this video and PDF.

 

[Jaysee62]

I have watched all of Mike Holt's videos (3 times) on how to verify the electrical system of a swimming pool is safe.
Still have a few questions.
1. Can I use properly sized aluminum THWN-2 wire from my main house service panel to feed my outdoor sub panel for the pool equipment?
2. Mike states in his NEV video to use the AC volt setting. I do this like he demonstrates and I get 0.1V and I have 0.1V at all the places Mike shows to check: bonding attachments, lead in the water, wet concrete deck and so forth.
The interesting thing I found is I read 194 mV DC at all the same locations. Mike says DC won't read NEV; however, I get a DC mV value.
3. Should I worry that I get DC NEV? OR is it ok as long as every point of contact in the required in the NEV test is the same 194mV DC?

 

[GoldDigger]

I have watched all of Mike Holt's videos (3 times) on how to verify the electrical system of a swimming pool is safe.
Still have a few questions.
1. Can I use properly sized aluminum THWN-2 wire from my main house service panel to feed my outdoor sub panel for the pool equipment?
2. Mike states in his NEV video to use the AC volt setting. I do this like he demonstrates and I get 0.1V and I have 0.1V at all the places Mike shows to check: bonding attachments, lead in the water, wet concrete deck and so forth.
The interesting thing I found is I read 194 mV DC at all the same locations. Mike says DC won't read NEV; however, I get a DC mV value.
3. Should I worry that I get DC NEV? OR is it ok as long as every point of contact in the required in the NEV test is the same 194mV DC?

1. Possibly, depending on where the terminations are located. Exposure to chlorine gas and chlorine or sulfur containing pool chemicals can corrode aluminum, including untinned aluminum wiring, to the point of failure.

Do Pool Chemicals Affect Aluminum?

Proper use of chemicals is key to a safe and sanitary swimming pool. Chemicals are used to disinfect pool water, control algae growth and for several other purposes, so a healthy knowledge of how to use these chemicals is essential for any homeowner considering installing a pool.

www.hunker.com

 

[Jaysee62]

1. Possibly, depending on where the terminations are located. Exposure to chlorine gas and chlorine or sulfur containing pool chemicals can corrode aluminum, including untinned aluminum wiring, to the point of failure.

Do Pool Chemicals Affect Aluminum?

Proper use of chemicals is key to a safe and sanitary swimming pool. Chemicals are used to disinfect pool water, control algae growth and for several other purposes, so a healthy knowledge of how to use these chemicals is essential for any homeowner considering installing a pool.

www.hunker.com

The wires terminate inside the outdoor sub panel which is located 48" above ground. Conductors are run in schedule 40 gray PVC conduit buried 20 inches deep.

 

[Jaysee62]

So,, anyone want to discuss DC Neutral Earth Voltage tests for equipotential bonding???

 

[Rjryan]

Neutral-to-Earth Voltage (NEV), NEC 2020, (44min:40sec)​

 

[Rjryan]

Mike Holt YouTube video on NEV, if you watch the video closely, Mike made a mistake on an actual test where the meter was set to DC and the meter would not register. Corrected himself put the meter on AC to register NEV.

 

[Jaysee62]

Thanks Rjryan. I've watched his video (and it is outstanding!) on NEV and how to find it and to use it. My readings are just as he says. I found it curious that I can get a measured DC voltage, which changed each day I measured it, and remained constant at each of the required test points.
I figure my measured NEV of 0.1 AC and 200 mV DC at all measured points indicates a safe pool environment as far as the equipotential bonding is concerned. Funny how in the past I've jumped into swimming pools without any consideration if it was a "safe" pool. And now, I'm hesitant to get in my new pool even after watching the installer put in the bonding grid and low-voltage LED lighting and doing all of the inspections Mike shows to do in his videos about pool safety 3 or 4 times. I guess ignorance is bliss!! LOL

 

[GoldDigger]

Two possible sources of a DC component of NEV are significant DC current through the earth, possibly related to rectifying loads or, for very small voltages, electro-chemical potential from large masses of different metals connected to utility pipes and the electrical system.

 

[kwired]

I'm not understanding the reasoning to even check neutral to earth voltage around a pool. Or at least to have many concerns about it. The whole point of equipotential bonding within the pool area is to equalize touch potential for pool users and it shouldn't matter if that whole bonded network is at a tenth of a volt to true earth or if at 1000 volts to true earth. Holes in the bonding system are what are potentially deadly to pool users even if a pretty low voltage exists to said hole.

On top of that there normally isn't much you are going to do about any voltage rise on the service neutral, especially if the reason for that rise is upstream somewhere in the utility company's conductors/equipment.

 

[Little Bill]

I'm not understanding the reasoning to even check neutral to earth voltage around a pool. Or at least to have many concerns about it. The whole point of equipotential bonding within the pool area is to equalize touch potential for pool users and it shouldn't matter if that whole bonded network is at a tenth of a volt to true earth or if at 1000 volts to true earth. Holes in the bonding system are what are potentially deadly to pool users even if a pretty low voltage exists to said hole.

On top of that there normally isn't much you are going to do about any voltage rise on the service neutral, especially if the reason for that rise is upstream somewhere in the utility company's conductors/equipment.

The reason is to check the NEV to get a baseline so that you can check the EPB in/around the pool to make sure it is correct. That is just one way to check the EPB.

 

[kwired]

The reason is to check the NEV to get a baseline so that you can check the EPB in/around the pool to make sure it is correct. That is just one way to check the EPB.

I guess that would assume your NEV remains stable while making tests.

I think I would be more comfortable using some kind of isolated source that I know will remain constant to get a baseline with. Have it grounded but via it's own electrodes and not interconnect it's grounded conductor with premises wiring system grounded conductors. Maybe even have it impedance grounded so that if there happens to be low enough resistance in the grounding electrodes that it would still be current limiting. Then connect the ungrounded conductor to the equipotential bond and check various points to the grounded conductor of said isolated system.

Just my thoughts but I would think it would be pretty effective and wouldn't have much error because the utility NEV happened to change while testing. In fact the impedance grounding would put current but with a limiting impedance on the equipotential bonding and would likely make holes in that network show up better than measuring NEV from utility supply through the network might do, partly because if NEV is low to start with you would be looking for low voltage differences instead of higher voltage differences where there is problems.

And with this isolated test source you would be looking for places with low volts instead of high volts when looking for compromised portions of the bonding as the EPB network would all be at a high level (how high depends on what you use for a source voltage) and any holes in the system will have a lower voltage to the grounded conductor.

If I am going down the wrong road with this that is fine, let me know what may be the flaws with it.

 

[Rjryan]

Mike Holt YouTube video on NEV, if you watch the video closely, Mike made a mistake on an actual test where the meter was set to DC and the meter would not register. Corrected himself put the meter on AC to register NEV.

I guess that would assume your NEV remains stable while making tests.

I think I would be more comfortable using some kind of isolated source that I know will remain constant to get a baseline with. Have it grounded but via it's own electrodes and not interconnect it's grounded conductor with premises wiring system grounded conductors. Maybe even have it impedance grounded so that if there happens to be low enough resistance in the grounding electrodes that it would still be current limiting. Then connect the ungrounded conductor to the equipotential bond and check various points to the grounded conductor of said isolated system.

Just my thoughts but I would think it would be pretty effective and wouldn't have much error because the utility NEV happened to change while testing. In fact the impedance grounding would put current but with a limiting impedance on the equipotential bonding and would likely make holes in that network show up better than measuring NEV from utility supply through the network might do, partly because if NEV is low to start with you would be looking for low voltage differences instead of higher voltage differences where there is problems.

And with this isolated test source you would be looking for places with low volts instead of high volts when looking for compromised portions of the bonding as the EPB network would all be at a high level (how high depends on what you use for a source voltage) and any holes in the system will have a lower voltage to the grounded conductor.

If I am going down the wrong road with this that is fine, let me know what may be the flaws with it.

How would you test the integrity of the grounded parts of a pool? How would you measure the quality of the ground terminations? You can check that there is no voltage between the bonded parts, but that does not insure the integrity or quality of the ground terminations. I am no expert, but it seems by using the NEV (voltage in ground) you are checking both the integrity and quality of the bonding system.
If you have a better or different way to do this after a pool is installed, please let me know.

 

[kwired]

Mike Holt YouTube video on NEV, if you watch the video closely, Mike made a mistake on an actual test where the meter was set to DC and the meter would not register. Corrected himself put the meter on AC to register NEV.

How would you test the integrity of the grounded parts of a pool? How would you measure the quality of the ground terminations? You can check that there is no voltage between the bonded parts, but that does not insure the integrity or quality of the ground terminations. I am no expert, but it seems by using the NEV (voltage in ground) you are checking both the integrity and quality of the bonding system.
If you have a better or different way to do this after a pool is installed, please let me know.

First thing what is going on in the pool is bonding and not grounding. We don't care about grounding in a pool we care about bonding things together so they are all at same potential.

Grounding is connecting to the earth, and generally has some significant resistance which will create voltage potential should there be current flowing. Bonding can have resistance but normally should be much lower resistance in the connections.

What I described is the same thing but going about it in a different way. NEV voltage is usually pretty low voltage, but as I mentioned can and will change as loading that causes this voltage changes. Im suggesting is introducing a likely higher and known stable voltage which will push current through the system and any weak connections will still show a voltage across them, but since higher test voltage to begin with should be easier to determine there is a problem when you do see a change in voltage in your readings. Either way you still need to know how to evaluate what readings you are getting mean.

This is a little comparable to using a megger on a motor instead of the low test voltage from a typical DMM to find insulation failures.