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#28769 - 08/29/03 07:20 PM Stray Voltage  
harold endean  Offline
Member
Joined: Feb 2002
Posts: 2,233
Boonton, NJ
A good friend of mine just wired up an inground pool. The pool was fiberglass, so there isn't much to bond to. There are a few cups for ladders and handrails and a 110 volt wet niche light fixture. It seems that they are getting a reading of about 10 volts from the pool to the ground. He was suppose to have pulled the electrical meter and still get some voltage readings. I am trying to contact him to sign on here and tell us the full stury. Anyone have any suggestions about stray voltage around a pool?

Harold


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#28770 - 08/29/03 07:26 PM Re: Stray Voltage  
Ron  Offline
Member
Joined: Mar 2002
Posts: 582
White Plains, NY
Make sure the 10V that he is reading is with analog meter. The input impedance of a digital meter might give a false reading (phantom voltage). http://www.nema.org/engineering/papers/PhanBull88.html


Ron

#28771 - 08/29/03 09:07 PM Re: Stray Voltage  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Er, be careful with the official NEMA “500Ω” recommendation. Ohm’s Law shows that to be a potentially dangerous situation if blindly followed. V²/R power dissipation for 120V and 500Ω is about 29 watts. {240V corresponds to about 115 watts} Either may likely turn a Radio Shack pegboard ½-watt resistor into an unexpected hot potato. The axial-lead resistor solution also makes a mockery of the safe design and listing of meter/test-lead combinations.

There are DMMs produced with a feature of dynamically low impedance “between 2kΩ and 100kΩ” to help limit false readings. With the popular 10-megohm input resistance, the best thing is to make damn sure the {probe} connections are not squirrelly—that they have “broken through” any surface oxides at the point of contact. The source impedance of most AC-power electrically energized sources is inherently low enough to make “safe”/high-confidence measurements with reasonably careful meter-lead connections.

Of course, if the checks are used to determine safe human contact, immediately-before-and-after known-live-source checks are straightforward common sense.


#28772 - 08/30/03 07:36 AM Re: Stray Voltage  
nesparky  Offline
Member
Joined: Jun 2001
Posts: 642
omaha,ne
Once had a simular problem near a pool. The power company's transformer had a bad neutral connection. Some of the service power was using the ground to try to return to source. This was picked up by the pool grounding thus making the pool ground ring a small voltage source (8-27 volts). This was enough to cause pool users to feel a shock when using a ladder to exit the pool.
It took a lot of time to find the problem. Th fix was easy for the POCO. Getting them to do it was a headache.
Good luck

[This message has been edited by nesparky (edited 08-31-2003).]


ed

#28773 - 08/31/03 04:51 PM Re: Stray Voltage  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
I can't stress the importance of Bjarney's post enough!

If anyone is planning to shunt the tester's leads with any type of fixed Resistor, make sure the results will not present hazards!

Try "Stepping Down" from a high Resistance (like starting out with 100K ohms), and work downwards to a lower value.

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#28774 - 09/01/03 10:55 AM Re: Stray Voltage  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,803
Brick, NJ USA
Harold:
?, are you in GPU/JCP&L area???

They have a stray voltage situation in Brick & other Ocean County areas that has been in the papers (Asbury Park Press) for a while. There is/was talk of earth return from utility lines/equipment. I'm not going to get into it here as it's not something that I know enough about to discuss correctly.

John


John

#28775 - 09/02/03 08:43 PM Re: Stray Voltage  
harold endean  Offline
Member
Joined: Feb 2002
Posts: 2,233
Boonton, NJ
John,

We are in the JCP&L territory. I was hoping the EC would contact me by now, so that I could get him to sign on this board and give us more details. I will try to contact him again this week and get him over here. I'll keep you posted.


#28776 - 09/11/03 08:52 PM Re: Stray Voltage  
harold endean  Offline
Member
Joined: Feb 2002
Posts: 2,233
Boonton, NJ
Some more on the pool wiring. This was a fiberglass pool. The EC ran the #8 cu bond wire all around the whole pool. He bonded the cups, dive board, motor, etc. to this bond wire. (As he should have.) The homeowner said that his children were getting a tingle, when they came out of the pool. He touched a meter, ( Don't know yet what type of a meter it was.) from the water to the earth ground, and got a reading of about 3-7 volts. This homeowner ( according to the EC) went around the neighborhood checking readings from front porch hand rails to the earth, water faucets to the earth, a neighbor's pool to earth, etc. to see if he got any voltage readings. He did get some readings here and there (1 to 7 volts) in several differnt places. I told the EC that I would post his story here and see what you guys thought about it and I was hoping that he would log on and join in. (Hasn't happened as of yet. I think his computer is acting up.)So I will relay any help that I get to him to help him with his problem. Thank you again for your help.


#28777 - 09/12/03 03:35 PM Re: Stray Voltage  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,803
Brick, NJ USA
Harold:
THe "problem" in Ocean Cty is something called SWER (single wire earth return), as the paper said. The utility says "NO".
GPU has had a crew in a few neighborhoods doing "repairs", and a foreman/supervisor and a consultant "checking for stray voltage"

Perhaps Bjarney, or one of the other members who are more familiar with line work can explain this further.

The way I got it, the "return" on the utility transmission lines is either to small, or it is bare/uninsulated. The article seems to be saying that they need a neutral, (insulated), but are using the bare "ground" instead.

I'm not one to "knock" the utilities, but down in Ocean County, GPU is taking a beating. The July 4th power outage on the barrier island, and neighboring mainland areas really got them a lot of heat.

As you said this situation is in GPU territory, perhaps you & your friend should go check out the Asbury Park Press on the web to read the articles. Had I known that this was not a "local area" problem, I would have saved the paper. If I see anything further, I'll let you know.

John


John


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