New pool with electrical shock

[Jose263]

Hi - I'm a newbie to the forum - We finally got our in-gound, vinyl liner, 16x32 pool, one light, light and pool bonded to the motor No ground rod at the pool site. Everything was inspected by the code office. 'Pool from hell' finished after weeks of many false starts and redos by the contractor -
We now have an electrical shock in the pool - when touching the concrete pad and water -concrete apron/pad does not have rebar and was not grounded. I read another discussion on this site that covered lots of possibilities.
The electrician and the utility company have tried to find the problem - no luck yet - however, we did find the possible source of the voltage 1.4V.
The electrician installed a sub-panel at the pump site and #6 - 3 cable from the service panel. the light is on a GFI circuit and bonded. Pump and saltwater system are wired to other breakers in the sub-panel.
The utility company completely disconnected service at the pole and pulled meter and ground at the entrance.
We still had the shock and 1.4v reading at the pool. Then we started disconnecting/testing the wiring at the sub-panel.
As it turns out, the voltage is coming from the ground (bare) wire from the #6-3 feeder from the service panel - even when the house is completely disconnected from the power line. BTW - the sub-panel has two buses - the ground wires are connected to one and the neutral wires to the other - When we connected the #6-3 ground to the neutral bus the shock stopped - but that doesn't meet code.
I just finished installing a new ground rod at the service panel yesterday - consensus was that the pool must have a better ground than the house and that should fix the problem - no luck. Haven't put a ground rod at the sub-panel - I guess that is next.
With all electrical power disconnected at the service panel I'm still getting voltage on the #6-3 ground - I'm thinking that the only voltage source left is the telephone - could that be the source of the shock? and how do I stop it?
Looking for help and experienced advice.
Thanks
TJ

[PoolDoc]

Looking for help and experienced advice.

Uh, me too!

I'm impressed by the quality of your investigation. It sounds like you have a 'difference voltage' caused by the notorious electrical villain, "the ground loop". (Wikipedia)

The problem is, there are all sorts of reasons why there might be a 1.4v difference between the potential at your pool and at your house's service panel. Your situation offers a GREAT example of what it's important to bond the deck as well. (I'm assuming that when you say "concrete pad", you mean concrete deck around the pool?)

Full bonding of all surfaces and gear around the pool would not eliminate the difference in potential between the house service panel, and the pool location, but it WOULD have eliminated any difference in potential between the pool and the deck.

A better ground at the pool may not solve the problem: there may be a 1.4V difference between the ground potential at the pool and at the house, and a better ground at the pool won't change that. If the voltage potential difference is a result of your electrical company grounding in the area -- say between a near by industrial or commercial feed with an unbalanced load, and residential grounds in your area . . . then putting a better ground by the pool may not change anything. Conceivably, it could even make things worse!

People forget (or don't know) that the power companies actually do use a common ground return to handle unbalanced loads; the "earth" -- dirt -- IS an element in these circuits. Almost by definition, the electrical companies are deliberately CREATING ground loops to balance these loads. If your pool is in the middle of an active 'balancing' circuit . . . you can add grounds till the cows come home, without solving your problem.

What probably would work, is extending your bonding mat to include every bit of metal on the pool you can reach AND adding a full buried wire loop around the pool that is also tied to your bonding mat.

(When he retired, one of my uncles was the chief maintenance engineer over all the hydro power network in TVA's Chattanooga region. So I called him and read him your post and my reply, and he essentially confirmed everything I said. He *did* note that these sort of problems never occurred until various forms of plastic pipe began replacing copper, iron & steel water pipes. When the power companies could bring that enormous network of metal pipes into their ground system, detectible ground loops were rare.)

[BigDave]

Do you have the 1.4V between the ground and neutral busses in the Service Panel? These busses should (code around here) be strapped to each other in the service entrance panel (but not in any sub panel). Ground and neutral are also usually connected together in the meter pan where the neutral/ground connection connects neutral to the driven ground. I would make sure that neutral is properly electrically connected to ground in the service entrance panel and in the meter pan as this is important to the safety of the electrical circuits in your home. I'm not sure that adding additional driven grounds will help, it may worsen any ground loop problem.

Is the light supplied from the sub-panel that supplies all other pool-touching circuits?

Ben is right (of course) that bonding the entire pool, pool water, and pool area (including every bit of metal larger than 4") should alleviate any shock as everything swimmers touch will be at the same potential.

[Jimmy C]

I had a similar problem. Went to change under water pool light, so turned off light switch, and breaker to GFCI circuit. Then measured no voltage black to white and either to ground. Safe to proceed right? There I was no shirt, tits on the wet ground removing pool light bezel. As soon as I detached it I started sizzling. Turned out the power coming off the utility pole had the bare neutral wire severed by a tree branch. The house ground was my pool, and the connection was at the light!! Any resistance in the neutral wiring back to the utility transformer can put voltage on neutral. Since neutral and ground get bonded together at main box, having a volt or two difference between pool ground an power ground is possible especially if the pool is far from the house. Sometimes the difference can be traced to a well pump that has lost its insulation, and is supplying current into the soil surrounding the well. Just some random thoughts! Jim

[Poconos]

I don't have any comments on how to solve your problem but am curious where your house and pool are located in relation to other houses. When I lived in New Jersey in a housing development you could stick a couple rods in the ground and get a voltage reading. Here in the country I get nothing. Ben touched on it when he was talking about power companies using the earth as a conductor. They don't do it intentionally but it is a fact of Ohms Law. Residential power is supplied by the live high voltage line and a neutral, or return, strung on the poles or underground. A transformer drops it to the 120/240 single phase for the house or houses. Because houses have these 'neutrals' connected to water pipes etc, part of the power distribution systems return current will flow through the earth thus creating a potential difference between your house and a neighbors. If neighbors are close this voltage gradient in the earth can be high. In the country with houses far apart it is a lot lower. Theoretically if all your pool equipment, rails, etc were connected to your service entrance neutral with a good heavy, low resistance wire, you shouldn't see this gradient.
I'be babbled enough.
Al

[Jimmy C]

From original post:

"As it turns out, the voltage is coming from the ground (bare) wire from the #6-3 feeder from the service panel - even when the house is completely disconnected from the power line. BTW - the sub-panel has two buses - the ground wires are connected to one and the neutral wires to the other - When we connected the #6-3 ground to the neutral bus the shock stopped - but that doesn't meet code."

The crux of the problem is in this statement. Both neutral and ground should be tied together at the main panel, and left separate at sub-panels. I'm not an electrician, but does #6-3 imply three wires #6, or 3 wires #6 and a ground? If it the last one, is the gauge of the ground wire the same (#6)? If we can eliminate the problem by jumping neutral and ground at the sub panel (not code), we should look upstream to the main panel. Are the two connected properly there? If so, take a meter from that point to a nearby ground rod (could be temporary 12" rod for this test). Is there any voltage from rod to main panel junction of neutral an ground? See illustration at the following link:

http://edis.ifas.ufl.edu/ae019

The dairy industry has similar issues where cows are extremely sensitive to stray electrical currents flowing in the soil, or concrete.

You might need a substantial buried ground plate(s) at the main panel. See link here:

http://www.erico.com/products/GroundPlates.asp

Jim