Question About Checking Equipotential Bonding

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Little Bill

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In Mike Holt's video (part 3) about pools and equipotential bonding he shows how he gets "neutral to earth voltage" (NEV). He goes 50' from the transformer and sticks a screwdriver in the ground and connects one of the leads from his DMM with a long cable to the screwdriver. Then goes to a pad mount transformer and touches the other lead to the metal cabinet of the tranny.

That I understand but I have a question... What if the tranny is a pole mount, what do you connect the other lead to? Maybe the ground wire from the tranny to GE?

I got a call wanting me to check a pool where they claim to be getting shocked. I was going to use Mike's method but most of the trannys here are pole mount. Even if they have underground to the house the tranny is still a pole mount. Just need to know what to measure to in that case.
 

Little Bill

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You can check form the main bonding jumper to "remote" earth to get the neutral to earth voltage.

Yes I know that. Mike did both 50' from the tranny, then 50' from the service. All I'm after is a reference and I suppose just one will get that but he used both readings.

Every pole trany I have seen has a wire coming down to earth

So just check to the wire coming down will yield the same results as checking to metal of a pad mount?
 

don_resqcapt19

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Checking at the transformer will not include the voltage drop on the neutral between the transformer and the main bonding jumper at the service. While normally small, this is a source of neutral to earth voltage.
 

don_resqcapt19

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If all of the code required bonding is in place, the neutral to earth voltage doesn't create a shock hazard at the pool. The required bonding keeps everything at the pool at this elevated voltage as measured to remote earth.

You need to start with voltage measurements between the points that resulted in the shock.
 

Little Bill

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If all of the code required bonding is in place, the neutral to earth voltage doesn't create a shock hazard at the pool. The required bonding keeps everything at the pool at this elevated voltage as measured to remote earth.

You need to start with voltage measurements between the points that resulted in the shock.

I understand that. But you need a reference to know what's elevated.
If you watch the video, Mike checks the bonding two ways.

1). Resistance check - where he first checks the resistance through his long cable by clamping at the ground bar of a timer or panel, if used, then back to enclosure. He then goes to the equipment.
Then he goes to area around the pool that should be bonded and checks resistance. He is looking for 1ohm or less difference.

2). NEV (neutral to earth voltage) - Where he does as mentioned earlier and sets a reference by checking from tranny and also from service MBJ.

The voltage to everything that is to be bonded should be very close to his reference voltage taking into account the load changing from POCO.

You may can understand it better from him if you watch the video.

https://www.youtube.com/watch?v=Q8YLcXRo-Go
 

don_resqcapt19

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I fully understand what Mike is doing, but I disagree with his selection of the transformer as the neutral to earth reference point as that ignores any contribution from the secondary neutral. If I am doing that test, I would start at the service grounding electrode or the main bonding jumper. By making the connection at that point on the system I have included the voltage drop on both the primary and secondary neutrals.
 

Little Bill

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I fully understand what Mike is doing, but I disagree with his selection of the transformer as the neutral to earth reference point as that ignores any contribution from the secondary neutral. If I am doing that test, I would start at the service grounding electrode or the main bonding jumper. By making the connection at that point on the system I have included the voltage drop on both the primary and secondary neutrals.

I didn't question anything he did as he did both from the tranny and the innersystem bond at the service. But he used the service reading to compare the rest of the items requiring bonding. Don't know why he did the tranny then at service. I'm sure he had a reason, he might have said but I didn't catch that on the video.
 

kwired

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I didn't question anything he did as he did both from the tranny and the innersystem bond at the service. But he used the service reading to compare the rest of the items requiring bonding. Don't know why he did the tranny then at service. I'm sure he had a reason, he might have said but I didn't catch that on the video.
It will tell you what the voltage drop is on your service neutral under current loading conditions, but that may not mean all that much when it comes to the functionality of the pool equipotential bonding.

The higher that neutral VD is the higher the voltage may be at any "holes" in the equipotential bonding though.
 

don_resqcapt19

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It will tell you what the voltage drop is on your service neutral under current loading conditions, but that may not mean all that much when it comes to the functionality of the pool equipotential bonding.

The higher that neutral VD is the higher the voltage may be at any "holes" in the equipotential bonding though.
Yes, Mike makes the point that the voltage will change with loading. The pool bonding is connected to the service grounding system via the EGC to the pool pump motor. It is my opinion that the service grounding point, and not the utility transformer should be the starting point for the type of testing that Mike is showing on the video.
 

kwired

Electron manager
Location
NE Nebraska
Yes, Mike makes the point that the voltage will change with loading. The pool bonding is connected to the service grounding system via the EGC to the pool pump motor. It is my opinion that the service grounding point, and not the utility transformer should be the starting point for the type of testing that Mike is showing on the video.
My opinion you should start at the service as well, or better yet at the point where the EGC for pool equipment gets connected to the rest of the electrical system, since it will not always be at the service equipment. Wherever that point is though should not normally have current flow which will mean there shoulnd't be any more voltage drop beyond that point. Only during fault conditions should there be any current.

Knowing the voltage drop of the service drop/lateral is mostly just a FYI thing but shouldn't mean much for the voltages you would measure around the pool vicinity if it is bonded properly.
 

don_resqcapt19

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...
Knowing the voltage drop of the service drop/lateral is mostly just a FYI thing but shouldn't mean much for the voltages you would measure around the pool vicinity if it is bonded properly.
If you just check the bonding to remote earth without knowing the neutral to earth voltage, your readings may be higher than you want to see. By knowing what the system neutral to earth voltage is, you can take that into account when checking the pool parts to remote earth.
 

kwired

Electron manager
Location
NE Nebraska
If you just check the bonding to remote earth without knowing the neutral to earth voltage, your readings may be higher than you want to see. By knowing what the system neutral to earth voltage is, you can take that into account when checking the pool parts to remote earth.
If POCO has a serious MGN issue, neutral to earth voltage may be near 7200:blink:
 

GoldDigger

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If POCO has a serious MGN issue, neutral to earth voltage may be near 7200:blink:

If POCO has a serious enough MGN issue to raise local earth to 7200V, then only customers whose pots are fed line to line will be continuing to get power. Odds of that vary greatly with the part of the country and local POCO practices.
 

kwired

Electron manager
Location
NE Nebraska
If POCO has a serious enough MGN issue to raise local earth to 7200V, then only customers whose pots are fed line to line will be continuing to get power. Odds of that vary greatly with the part of the country and local POCO practices.

Well it would likely not be something that goes on for a long time unlike a rise of a 10-50 volts possibly could go for a long time before it raises concerns somewhere.
 
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