gradient voltage

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a rate of change with respect to distance of a variable quantity

a rate of change with respect to distance of a variable quantity

I guess it's the electric field strength change, in the ground or in the water, as you get farther away from the source. The ground or the water has a bulk resistivity, and so weakens the electric field by shorting it out.
 
It is the voltage gradient in the ground surface or the surface of the pool wall. Voltage gradient is the difference in voltage with distance and is caused by current flowing through a resistive material like concrete or soil. If the reinforcing steel in the pool walls is properly grounded, the pool wall becomes an equipotential surface and there is no voltage gradient. The main point is to get everything bonded together and connected to the EGC and thus back to the service main bonding jumper.

The ground rod doesn't reduce voltage gradients very much. I don't think a supplementary ground rod is a code violation, but it serves no real purpose. It certainly can't replace connection back to the service over the EGC without being both a code violation and an extreme safety hazard.
 
This guy Zipse ,.not sure he is right ,.. is responsible for some of the best substantiations ever brought foward,.. in my opinion anyway.


.........The Electric Power Research Institute (EPRI) an organization of utilities
companies states that 40 to 60 percent of the return neutral current from the
high voltage electrical circuit returns over or through the earth. We have
measured as high as eighty-eight (88) percent of the neutral current returning
over the earth and thus through dairies, back yards of homes through hot tubs,
swimming pools, etc.
Ohm?s Law states that Voltage = Current X Resistance
It is impossible to eliminate voltage gradients, except in your imagination
as long as current is flowing continuously through the concrete and re-bar,
which is happening in the real world.............
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It is impossible to eliminate voltage gradients, except in your imagination as long as current is flowing continuously through the concrete and re-bar, which is happening in the real world
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That is correct, however the bonding can reduce gradient to the point where it does not cause problems. It is my opinion that there should be no electrical connection or metallic parts of electrical equipment in contact with any part of the pool or its water. If we built the pool like that then the we would not have to connect the pool bonding system to the electrical grounding system. The way we do it now we are required to energize the pool bonding system by making a connection to the electrical grounding system. This engerizes the pool bonding system with a voltage equal to the voltage drop on the utility primay and secondary grounded conductor.
 
jghrist said:
The ground rod doesn't reduce voltage gradients very much. I don't think a supplementary ground rod is a code violation, but it serves no real purpose. It certainly can't replace connection back to the service over the EGC without being both a code violation and an extreme safety hazard.
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I agree, and didn't mean to imply that a ground rod in itself would be a code violation. I should have stated that using the ground rod for anything other than supplementary (now auxiliary, 2008 NEC) grounding would be a violation.
 
This is another of my favorites from Mr. Zipse

What happens is the equipotential plane is such a good, efficient low
impedance contact with the earth that the equipotential plane acts as a ?sink?
for the majority of the stray neutral current flowing through earth in the
vicinity. It becomes a magnet for collecting the stray current. This equipotential
plane is connected to the equipment grounding conductor which is connected to
the neutral service entrance conductor which, is connected to the utility power
company?s transformer which has the secondary neutral connected to the
primary neutral thus completing the connection to the primary electrical circuit
back to the transformer.
What should be done is to connect all conductive metallic surfaces that can
become energized to the grounding system through bonding conductors. No
more, no less just as would be done in a home or industry.
No doubt, someone will make the comment that equipotential planes must do
some good, must have a little advantage or may afford some help. That person
needs to face the facts ? THERE IS NO BENEFIT IN ANY WAY, SHAPE
OR FORM FROM EQUIPOTENTIAL PLANES, ONLY HARM. The
concept was based on erroneous ideas and conclusions and mis-understanding
of electrical principles.
If equipotential planes were such a great idea, why not require the basements
and garage floors to have equipotential planes in case someone walked on the
floor in their bare feet? Now watch some panel think that this is a great idea. A
fool is born every code cycle.
The dairy farmers in Wisconsin long ago deleted from the state adopted
NEC the sections on equipotential planes as they realized the danger and
hazards equipotential planes presented to dairy farmers.
Panel Meeting Action: Reject
Panel Statement: The panel does not agree with the submitter?s
substantiation.
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the reason for the grounding structure is the free flow of electrical currents due to the condition of the soil located around and under the concrete..it is cool and damp most of the time which cause the soil conductivity to increase with the amount of moisture present..the bonding of the rebar and making of the plane is to help reduce the hazards associated with the damp conditions of the soil..

I hope this helps in the explaination you are looking for..I also agree that a ground rod would not be of any real value in this type of install..
 
The important thing with pools is bonding. This will keep all metallic parts at or near the same potential. If everything is at the same potential there is no current flow. Grounding a pool is not required. The pool is installed in or on the ground. It is in contact with the earth. It is already "grounded". Installing an auxiliary ground rod will do little to make it more grounded!
 
From a Mike Holt News letter,.. at some point we will need "equipotential" bonding everywhere ,. I bet I live to see a major change in the multi grounded neutral system.

http://mikeholt.com/mojonewsarchive...ay-Pool-Voltage-from-an-Engineer~20040630.php



So, with the swimming pool, there are multiple references. There is the earth, which we have conveniently labeled as zero volts. There is the utility neutral, which will always have voltage on it due to the use of single-bushing transformers. If the earth were a perfect conductor, there would be no elevated voltage on a utility neutral because the earth would be a super-conducting path for all the neutral currents. If the pool itself had no connection to the electrical system, this would not be a problem. But the pool has pumps and filters which are powered by the local electrical company. The water runs through pipes and the enclosures of the pumps. The water becomes the same potential as the electrical enclosures (some call this stray voltage). The electrical enclosures are bonded to the electrical system. No matter how you do it, the pool is eventually connected to the utility primary neutral and its elevated voltage.

Grounding the pool doesn't get rid of this voltage (It's already grounded) because the earth is not a super-conductor. All grounding will do will be to create a potential gradient on the soil around the ground rod. The thing to be aware of here is that the pool will be a certain number of volts above the earth.

Will this potential gradient ever be in a location where barefoot swimmers could access it? For example, with one foot on the soil outside the deck and one foot on the deck? Something to consider when you build your next pool.

Oh, and by the way, make sure you use standard rebar in the shell of the pool. Epoxy coated rebar does not provide the conductive structure necessary to bond the shell.

I hope I haven't confused the issue.

Eric Stromberg, P. E
Houston, Texas
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