Maybe someone can expain this to me.

I'm working with my plumber on a job. We are installing an underground water tank to use for a small coy pond and an irrigation system. The tank is fed from a small creek and has a submersible pump. I had all the wiring done and the well guy was wiring the pump in the tank and got shocked. They called me and asked me what the problem was. I'm thinking, oh crap, did I leave the disconnect on, did I wire it wrong, etc. The disconnect was off. Apparently I have got some stray voltage on the egc. He got a shock off the ground. When I go back to the panel and turn off the main I get 2v from the egc to earth ground. Is this a utility problem and how do I diagnose it? I wasn't there when he got popped but it was enough to make think about it.

how close to other GEC's wuz the plumber schenimann ?

~S~

The first questions are "is this fed off of a sub panel? Is the neutral bonded there?"

You might be seeing the voltage drop in a 3 wire feeder.

If so that is where I would start.

You should know "ground" is not always "zero volts". That is why we have article 682.

Are you SURE the guy wiring the well pump didn't transpose a couple of wires?
What I'm saying is you can bond and ground everything to the 9th degree, but not enough "let-through" current will happen to blow a protective device.
This is why plumbers should stick to running pipes and leave the complex stuff to us.

Trumpy, you will find "ground" is not really "zero volts" from point A to point B. That is why we have ground electrode systems, article 680 and in this case 682. Once he establishes his equipotential plane and attaches it to the equipment, hence the EGC, everything will be "zero volts" again.

This is simply the consequence of using the earth as a return path for circuit current. I know we say that is not supposed to happen but current takes all paths and that grounded PoCo transformer shares the earth with the grounded service drop conductor. The grounded transformers on L/N transformers also share earth with the grounded conductor going back to the sub station.
Current is flowing through the earth all over the place and there will be some voltage difference between each ground electrode along the way.
To see this, all you have to do is look at the current flowing in that #8 coming down the pole.

The circuit is fed from a meter combo, ground and neutral bonded together. From that egc to earth I get the voltage. Is that voltage just floating around in the earth? If so then I am not worried or is it something that needs to be looked at. It actually had nothing to do with the plumber, it goes all the way to the service.

It's normal and can get quite high. I've seen over 110 volts between a building with a ground grid and a ground in a teck cable feeding that building from a source few hundred feet away. Where I am, the rural distribution is single line and uses a ground return, so the higher voltages might be unique to my area.

Far be it for me to drop a spanner in the works, but this has to be sorted before you put any fish in the pond!

What your describing sounds like a utility company problem. I would have them check out their system. Ive dealt with this before on diary farms and pools. It comes from the utility company having an insufficently sized neutral or a break in it somewhere and the ground is taking up the slack. Normally the pocos are resistent to the problem and its not uncommon for them to deny it all together. Talk to them though there is a device made that can be put at their transformer that seperates the customer's neutral from the poco's.

I still think this is pretty normal. That is why we have several articles in the code about establishing an equipotential ground array where these objectionable currents will cause problems. (pools, spas, farms and bodies of water).

My bet is that if you could really find a "ground", whatever that is (maybe the ocean), the pond would be grounded and the GEC of the service would be 2 volts above that. Considering all the losses along the way from the power plant, I am surprised it is only 2 volts.
If I was trying to mitogate it I would either increase the size of the ground electrode system at the service or reground the EGC at the pond (the ultimate effect of article 682)

A little Gee Whiz info

I see 0.14 to 0.15 difference between the EGC at my house (right at the service disconnect) and the ground electrode on the pole where the transformer sits, 50' away (that is a 14ga, 50' extension cord)
The .14-.15 change seems to be whether the (120v L/N) washing machine is running. I could hear it cycle.

This is the voltage drop in 50' of service drop.

I suppose I should have looked at the neutral current.

Is the cold water pipe cu? Do you have good ground rods? Connections. Sounds like you have a bad trans from the power co. if its happening w the main off. and your grounding of the service is not doing its job very well or is doing the whole job and your plumber friend found a little better path to ground. I just finished with a similar problem. The cold water clamp was loose and customer noticed it was arcing and his lights were blinking/flickering. I tightend it and the problem went away. After many calls and visit with the POCO they decided it was a bad trans. It seems the neighbor had a problem too and didn't know it. He paid another sparky weeks before to change his panel LOL.

Ob

I have a 15,000 gallon concrete swimming pool. You don't get a better grounding electrode than that. Add a Ufer ground, a couple thousand square feet of bonded deck and 4 ground rods and I think I am grounded pretty well.

A bad transformer does not cause elevated ground voltage. As for tightening up the the ground water clamp your just masking a dangerous hazard called an open service neutral. The op should have the poco do a double check that everything is ok on there end and also try to make an equal potential grid to eleviate the symptoms.

There is voltage drop in any conductor, that will show up as ground shift.
When you have wye distribution there is also voltage drop in the grounded conductor on the pole. Some current has to be returning through the earth.

Since I have a 13kv distribution line that runs pretty close to a tidal river (that I assume might be as close to true ground as possible) I may extend this experiment along the line of about 20 transformers. I just need to come up with a 150 foot meter lead and a decent electrode.

BTW when I did my current testing a while ago in this transformer string, I still had current in my grounded conductor to the EGC with the service disconnect open.
As I said, I probably have the best grounding electrode system in the neighborhood.