[logi98]

I talked with a friend with an in-ground pool. He gets a slight electrical shock when getting out of pool (half in water and touching the wet cement walk around pool). He asked me how that was possible. I replied that there has to be defective or no electrical grounding. He has turned off all circuit breakers (cb) to both motors and the lights. A slight potential was still there. Also, he has measured for vac leakage out of cb'ers and potiential was still there. I've read about grid bonding and assume this is a possibility. Yet I think there still has to be a hot wire around the pool for the potential. Lastly, I wonder about the ground (earth) at pool pump verses the power company ground. What if his ground was better than the power company ground? This would also create a difference of potential. Any advice/recondementions would be greatly appreciated. Also, I advised gfci circuits.

Thanks, Logi98

 

[spark plug]

Getiing slight shock on concrete while getting out of pool

Installing a GFI breaker on the Pool pump motor circuit is a good idea, and probably a Code requirement. But the "Shocking" mystery must be solved first. If, as you say you turned off all circuits and still getting shocked, there's a possibility that a "renegade" live wire is left from a previous installation!:yes::no::devil2:The devil is in the Details! Don't Drink and Drive!!!

 

[Speedy Petey]

This is an issue of a poor bonding grid, or not having one at all. This is not a "hot wire around the pool" issue.

The ground from the POCO is actually from the neutral bond in the main panel. The earth itself has nothing to do with the electrical ground that causes breakers to trip on a short circuit. So adding a wire from a motor to the earth or a ground rod will serve absolutely no purpose.

Read up on "equipotential bonding". Google is your friend.

 

[Stubbie]

I'll just start by saying there is nothing we can do here to solve your problem other than point you in the right direction.

I would like to mention that Speedy is correct your friend likely has a defective bonding grid for his swimming pool or an improper one or none at all. However you should understand that current exists in the earth almost everywhere and it may be a result of stray voltage and or current (neutral to earth current) or fault current. Question is.... is it excessive and where is it coming from? This is all due to the utilities multi point neutral grounding system where earth and the utility neutral play partners in returning neutral current to the source (transformer). It is important to note that stray current is not fault current.

You need to request an inspection by a codes official who will then request a NEV (neutral to earth voltage) analysis from a power company technician/engineer.

They will likely begin by asking you to turn your main breaker off. They will then take a test measurement of NEV around your pool. If the NEV deminishes to an acceptable level then the problem is with your electrical system.

If it doesn't decrease then they will pull the drop out fuse of your transformer. If it still doesnt decrease then it is a utility neutral problem or a service neutral from a closeby neighbor or some other outside source. They likely will install a neutral isolater device to solve the stray current and or voltage problem if it is coming from the utility.

Proper bonding of metal around the pool will generally eliminate potential differences but will also mask a stray voltage/current problem.


So two things

1.) You need to be sure you have a bonding grid around your pool in accordance with NEC article 680.26 2008
2.) Have a neutral to earth voltage analysis done (NEV Test) to determine if it is your problem or the utilities or if no problem exists other than improper bonding of metal around your friends pool. And if it is stray voltage and current or fault voltage and current.

 

[logi98]

reply to grid bonding

I understand the grid problem, however, for there to be a difference of potential doesn't there have to be a potential or leakage from a hot wire? With all circuit breakers off and no leakage has been measured how else could there be a shock hazard?
Thank ......logi98

 

[Stubbie]

Nope, neutrals are current carrying conductors and therefore have potential though not of the magnitude of ungrounded (hot) conductors. A hot to ground is a fault and is not considered stray voltage. You need to determine which it is. However don't test by seeing if you still get shocked it may be your last one.

 

[logi98]

Thanks for your help. If there was a bad neutral connection at the power company (pole) then would the pool have a better ground causing a difference in potential between the two points?
Thanks, logi98

 

[Stubbie]

No it would be no better than the transformer ground. Remember all neutral taps at the transformer also have an earth grounding conductor ran to a ground rod at the bottom of the pole. Turning the main breaker off at your home will effectively remove all neutral current on your side of the service entrance unless neutral current is getting to the pool through the earth from an outside source. An example would be a buried lateral service to a neighbors or your lateral service that has a faulted neutral to earth or even a hot to earth that is placing your pool and surrounding metal in that potential gradient as the current uses the earth to get back to the source (transformer). The pool just happens to be in the way....

Suffice to say you have a stray or fault problem at your friends pool as you should not get shocked if you have a equipotential grid that is properly installed. It is likely that getting shocked is not normal to say the least and I would suspect you have a fault on the homeowners side of the utility or you have a stray voltage problem originating on the utility side of your service.

When your friend gets out of the pool is he touching a metal hand rail or just getting out onto wet concrete?

 

[logi98]

To my understanding he gets a slight shock getting out onto the cement and the shock is worse if it is wet. He has measured less than 3 vac from the ground rod at the pump to the pool water or wet cement.

 

[Stubbie]

Have your friend turn his main breaker off and take a measurement from the concrete to a metal object... the pool pump would be good. See if the voltage disappears or reduces. Do not place yourself in series with any concrete or metal around that pool. BTW the ground rod at the pump, if that is what they are using to ground directly to the pump, is pointless.

 

[logi98]

With the cb'ers off he measures about 3 vac from the ground rod beside the pump to the wet cement. He mentioned that when he removed the copper grounding wire from the rod and measured from the rod to cement the voltage dropped to about 1.5 vac. All this information I'am passing on was from a phone conversation with him earlier this afternoon. I might need to go visit and see exactly what he is doing.

 

[Stubbie]

Is that ground rod for the pump only or is it the ground rod for his electrical service.....and he is grounding the pump to it ? The pump should not be connected/bonded to any earth driven rods. It should be bonded to the other metal and equipment around the pool.

 

[logi98]

There is a power panel at the pump house with the grounding rod. This power panel is seperate from the house panel which also has a grounding rod. What is BTW? Also, he is in the process of "rent-to-own" for this house.

 

[Stubbie]

Gotta go for the evening.

FWIW 3 vac is about where most people will complain of tingle voltage. Measuring 1.5 volts to the earthed rod and the concrete would be in the realm of an acceptable stray voltage. I would expect that.

Heres something to read through while I get some sleep....:thumbsup:

http://forums.mikeholt.com/showthread.php?t=86958

 

[logi98]

Thanks Stubbie, catch you tomorrow. Thanks for all your help.................logi98

 

[Stubbie]

Your welcome...good night


BTW...By the way

FWIW....For what its worth


:thumbsup:

 

[Ultrarunner2017]

I'm not an electrician, but my common sense tells me that all equipment (pump, lighting, etc) housings, and all metal parts around the pool should be bonded to the SE ground. Also, if there is a sub-panel for the pool, its neutral should NOT be bonded to the ground in the sub-panel, but the ground of the sub-panel should be bonded to the SE ground. Neutral from the sub-panel must be bonded to neutral in the SE panel.
So, you have a continuous ground conductor from the SE to the sub-panel, to the equipment housings, and metal parts around the pool.

Instead of shutting off all circuit breakers, shut off just the MAIN breaker at the SE. If there is a problem inside the SE panel, it is possible for current to "leak" around the individual breakers. You want to be sure everything is dead, then check voltages as you have before, and whether or not your friend still feels a slight shock when getting out of the pool.

I agree with the advice on getting an inspector.
If POCO is at fault, make them fix the problem.

If all fails to find/correct the problem, check for stray RF in the immediate area. Your friend doesn't live next to a radio station transmitter, does he?

FW

 

[Stubbie]

There is a power panel at the pump house with the grounding rod. This power panel is seperate from the house panel which also has a grounding rod. What is BTW? Also, he is in the process of "rent-to-own" for this house.

Might want to visit with the owner about his problem and see if he will get involved with a solution to the tingle voltage. Also remember it isn't so much the voltage that tingles you what your feeling is current flow.

The ground rod at the pump house is required for the electrical system protection and equipment protection from lightning and utility power surges.
The pool pump does not need to be bonded to that ground rod it is already bonded to the grounded conductor and earth at the main panel of the house via the equipment ground ran with the pump branch circuit conductors and pump house feeder.

These tingle voltage problems are very difficult to solve in many cases and should be handed over to qualified people who deal with this stuff all the time. There are a few things you and your friend can check and you may get lucky and solve the issue. But if you find yourselves chasing your tail get someone in there, with the owners permission, that has experience with this kind of problem around a swimming pool. It may be a bonding problem or it may be there is an external or on premise issue causing the unwanted voltage and current.

BTW...the lug on the pool pump is to bond it to the equipotential grid around the pool . This is done with a #8 copper wire ran to all required metal around the pool. Concrete walkways should either have rebar in them that you can bond to or a metal grid the concrete was poured over to make your bond to the common grid. I would suspect there is no ability to bond the walkway around the pool or there is no equipotential grid installed and no metal bonded. Voltages like 3 vac should be eliminated, as far as tingle voltage felt by people, by proper bonding to a equipotential grid.

If there is no grid then it will be pretty much impossible to get rid of the tingle voltage if it proves to be with in tolerence of what is expected for your area. Finding the source of the current or voltage is about the only way a solution will surface.

 

[Yoyizit]

You might try loading down the 3 vac with a 7-1/2w or larger incand. bulb and see how much it drops, so the bulb is in parallel with the voltmeter. This drop in voltage along with the "cold" resistance of the bulb will give some idea of the (Thevenin) resistance of the source supplying this voltage.

With ~8 mA of AC current flowing, this guy's skin/body resistance must be 400 Ω.
http://www.easternvoltageresearch.com/datasheets/safety.pdf
assuming his body saw the same voltage that the meter did.

What kind of soil resistivity do you get in Florida?

soil 30k to 50M ohm-meter
tap water 1M to 100M ohm-meter
concrete 200 ohm-meter
human body 5 ohm-meter
copper 20 nanoohm-meter

 

[Stubbie]

I'm not an electrician, but my common sense tells me that all equipment (pump, lighting, etc) housings, and all metal parts around the pool should be bonded to the SE ground. Also, if there is a sub-panel for the pool, its neutral should NOT be bonded to the ground in the sub-panel, but the ground of the sub-panel should be bonded to the SE ground. Neutral from the sub-panel must be bonded to neutral in the SE panel.
So, you have a continuous ground conductor from the SE to the sub-panel, to the equipment housings, and metal parts around the pool.

The bonding of metal around the pool was never meant to be part of the equipment ground of the electrical systems feeders and branch circuits... which is for fault currents and tripping out breakers not stray voltages that appear as earth gradients in contact with the pool and surrounding area. The bonding of all metal around a pool is to get all metal and walkways that come in contact with a stray voltage gradient to come to the same potential as the stray voltage gradient and prevent a shock to people if this occurs. It is not intended to be part of the effective ground fault path back to the SE.There is always a voltage /current gradient in the earth by the very nature of the way utilities ground (earth) the electrical distribution system. Bonding prevents this product of the utilities from shocking you around the pool when walking on concrete or touching two conductive parts around a pool. These gradients that are allowed and others that are not supposed to be present is why we join metal around the pool to the equipotential grid. Joining them to the egc going back to the SE provides no additional safety to stray voltage.

Note that there is a non-intentional connection at the pump (if it isn't double insultated) and heater by the vary nature of the egc and bonding wire terminated to the metal frame of the motor. If the pump is double insulated there is no bonding lug and it is not required to be connected to the bonding grid around the pool and as a result will not be incidently connected to the egc of the pump branch circuit.