Pool Bonding

J

Jimmy7

Senior Member
Location
Boston, MA
Occupation
Electrician
If I want to check how well a pool is bonded I should measure the NEV, correct? I think I saw a video that Mike put out about it a while back. Does it matter where you put your reference point? If I remember correctly Mike put a screwdriver or a stake in the ground near the meter socket. When checking the different locations with your meter do all the voltages need to be exact, or can they vary a little? What's acceptable? This is not for certification purposes, but If I ever wanted to check if a pool is bonded properly
 
The temporary ground rod or reference should be well away from any grounding electrodes or metal underground piping...this remote earth is often defined as being at least 50' from any other grounding electrode.
Ideally you have two meters to read at the same time as when the loads change so does the neutral to earth voltage. One meter connected to the GEC at the meter and the other end to the temporary grounding electrode. The second connected to the temporary grounding electrode and the other end to the parts of the pool that you are checking. The voltages should be pretty much the same...maybe a 0.1 volt difference at the max.
 
don_resqcapt19 said:
The temporary ground rod or reference should be well away from any grounding electrodes or metal underground piping...this remote earth is often defined as being at least 50' from any other grounding electrode.
Ideally you have two meters to read at the same time as when the loads change so does the neutral to earth voltage. One meter connected to the GEC at the meter and the other end to the temporary grounding electrode. The second connected to the temporary grounding electrode and the other end to the parts of the pool that you are checking. The voltages should be pretty much the same...maybe a 0.1 volt difference at the max.
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Just for clarity. Could you give an example of what you might see on both meters.
 
Jimmy7 said:
Just for clarity. Could you give an example of what you might see on both meters.
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Too many variables, but often you will see a couple of volts. If over 5 volts, I would thinking there is some type of neutral issue, and that could be on the utility primary if the transformer primary is connected line to neutral.

The voltage is not really important for proving the pool bonding. Having the voltages the same at all of the test points is what shows the pool is correctly bonded.
 
A conductive permanently installed pool shell is basically like a faraday cage with an open top, in that no matter what the voltage of the earth is it keeps all parts of the water at the same potential. To do that all the metal parts of the pool form a grid with a extremely low ohm resistance.
it has more to do with the pool water than the electrical system.
In theory if you built a nice in ground gunnite pool with no electrical equipment, no electric pumps no lights, at a site that did not even have an electrical service it would still need the equipotential bonding grid.
The section in the 2023 NEC 680.4 that suggests 'periodic inspections and testing' of pools is a interesting topic,
The typical tool for testing low ohm's is a Precision Milliohm Meter, one could presumably use a mili ohm meter to test various points in a pool and record the values. You'd have to get into the weeds of low ohm testing a bit, I have not seen any NETA or other standards for testing a pool equipotential bonding grid.
 
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tortuga said:
A conductive permanently installed pool shell is basically like a faraday cage with an open top, in that no matter what the voltage of the earth is it keeps all parts of the water at the same potential. To do that all the metal parts of the pool form a grid with a extremely low ohm resistance.
it has more to do with the pool water than the electrical system.
In theory if you built a nice in ground gunnite pool with no electrical equipment, no electric pumps no lights, at a site that did not even have an electrical service it would still need the equipotential bonding grid.
The section in the 2023 NEC 680.4 that suggests 'periodic inspections and testing' of pools is a interesting topic,
The typical tool for testing low ohm's is a Precision Milliohm Meter, one could presumably use a mili ohm meter to test various points in a pool and record the values. You'd have to get into the weeds of low ohm testing a bit, I have not seen any NETA or other standards for testing a pool equipotential bonding grid.
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One of Mike Holt's pool video shows that the actual resistance of the bonding is not important as the bonding is not carrying current...it is equalizing the voltage potential. I think he use a 100k resistor in one of the videos to show the resistance is not that important.
Because he found the resistance to have little impact, he suggest the voltage testing to verify bonding.
 
don_resqcapt19 said:
One of Mike Holt's pool video shows that the actual resistance of the bonding is not important as the bonding is not carrying current...it is equalizing the voltage potential. I think he use a 100k resistor in one of the videos to show the resistance is not that important.
Because he found the resistance to have little impact, he suggest the voltage testing to verify bonding.
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However a low resistance path need to clear fast
line to ground fault hapoen
Or dangerous potential gradients in pool area till ground fault clear
 
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Deltaforce said:
However a low resistance path need to clear fast
line to ground fault hapoen
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That is not the purpose of the pool bonding. If it was the code would not say:
680.26 ...An 8 AWG or larger solid copper bonding conductor provided to reduce voltage gradients in the pool area shall not be required to be extended or attached to remote panelboards, service equipment, or electrodes. ...
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Purpose the pool bonding ensure pool
equipotential grid
But for fault current flowing pool, pool equipotential grid need ocpd/GFCI operation mitigate dangerous potential gradients pool
 
Deltaforce said:
My concern during fault clearing equipotential status present or not
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If the bonding required by 680.26 needs to provide to provide an effective fault clearing path, 680.26 would have to be completely rewritten. There is no intention that the equipotential bonding required by 680.26 serve as an effective fault clearing path.
 
don_resqcapt19 said:
If the bonding required by 680.26 needs to provide to provide an effective fault clearing path, 680.26 would have to be completely rewritten. There is no intention that the equipotential bonding required by 680.26 serve as an effective fault clearing path.
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But 250 foundation for grounding and bonding for pool circuits also?
 
Deltaforce said:
But 250 foundation for grounding and bonding for pool circuits also?
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Absolutely not.
250.52(B) Not Permitted for Use as Grounding Electrodes.
The following systems and materials shall not be used as grounding electrodes:
  • (1) Metal underground gas piping systems
  • (2) Aluminum
  • (3) The structures and structural rebar described in 680.26(B)(1) and (B)(2)
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Also the grounding electrode system is not a part of the effective fault clearing path.
 
Across the bridge in NJ I think they require testing of pools or public pools now I dont know what they test or how often.
And of course a pool grounding grid is 'electrically conductive material' that needs to be installed in a manner that 'creates a low-impedance circuit facilitating the operation of the overcurrent device', that is accomplished by the connecting the EGC at the pool motor and the #8 from the pool motor to the grounding mesh. I would be amazed if Mike said otherwise. And I agree its not a electrode.
 
don_resqcapt19 said:
Nothing in the pool bonding system is covered by that code section. as it is not likely to be energized.
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What in the world ? Are you speaking for Mike Holt when you say that as an Employee of Mike's site?
680.26 covers pool pump motors under water lighting etc, all kinds of things would be likely to energize a pool grid, its DIY misinformation to say those would not be likely to become energized.
 
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