Stray voltage problem.

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Paul Allen

Electrical Contractor
Location
Middleburg Florida
Occupation
Electrical Contractor
Recently I was called to a service call for a customer who was recieving a shock getting in and out of his recently built inground swimming pool. A Check of the system showed all of the grounding connections in place, neutrals and grounds proper, and the best i can tell, the pool grounding was installed properly. When the customer gets in and out of the pool, he feels a tingle. I checked the voltage between the pool deck and the water and get about .7VAC. The kicker to this, and where I think the problem is coming from is a High voltage power line on the opposite side of his next door neighbors house. (approx. 100' away.) Voltage measurements from the water to the ground under the power lines are 2-3 VAC., and they lessen the closer to the pool you get. I really think that is the source. I put my clamp on ground tester on the #8 bonding jumper and was reading 70 MA of current flowing on the wire.
My estimation of this problem is that the stray voltage is coming from the high voltage lines thru the pool grid and is going thru the customers equipment ground on the pool motor.It is going thru his service panel and going back to the source thru his utility transformer connection. I removed the #8 bonding jumper from the metallic motor housing and timer housing and the current flow went to 1-2ma and the customer says he is not recieving a shock. (I realize that leaving the bonding jumper off the motor equipment is a violation of the NEC, but the equipment is not in close proximity to the pool). I am wondering if anyone has any other suggestions, something i can try to remedy this situation, or something I havent thought of. Thanks in advance for your response.

Paul Allen
Florida Master Electrician
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
I think you've got the right idea, just backwards. The utility voltage is coming in on the service neutral, and diving into the earth at the pool.

If you search for the "Ronk Blocker" it is billed as being able to block the utility primary neutral from using your pool as a path to return to it's source. I've never used it myself (never had this problem personally).

I recommend shutting off the pool equipment as long as you have any bonding undone for troubleshooting. If anything happens, related or not, you'll be liable for consequences.
 

ghostbuster

Senior Member
We had a community pool with exactly the same problem.First and foremost we shut down the pool right away to avoid liability issues (pacemakers failing,shocks etc.)We then isolated the primary neutral from the secondary neutral with all the necesaary inspection approvals.Problem solved.:)
 

jtester

Senior Member
Location
Las Cruces N.M.
If the problem disappears when you disconnect a bonding jumper, I wouldn't be sure the problem is coming from induced voltage from a nearby power line. The suggestion of a Ronk Blocker is a good idea if the stray voltage is being produced off site, I don't think it works with an induced voltage. You should check to be sure the source is not on site before resorting to the blocker.

Jim T
 
If you are reading a voltage potential from the pool to the surface around the pool, it sounds to me as though your "Equipotential Grid" of the pool and area around the pool may be incorrectly installed.
If the pool bonding (not grounding as has been mentioned- we do not ground pools, we bond them...not bonding for the sense of opening an overcurrent device, but for Equipotental grid plane), is correctly installed I do not see how there exists a potential from the pool to the deck. Unless of course the pool may be a nonmetallic pool with a conductive surface around the pool, then I can see this issue developing.
 

ghostbuster

Senior Member
ghostbuster said:
We had a community pool with exactly the same problem.First and foremost we shut down the pool right away to avoid liability issues (pacemakers failing,shocks etc.)We then isolated the primary neutral from the secondary neutral with all the necesaary inspection approvals.Problem solved.:)

Just a note to add to our earlier post.When the grass was wet,the kids in bare feet would get "lifters" when they touched the chain link fence located around the ball diamond ,located approx.100 feet away from this pool.This was "solved" by the townspeople many years earlier by replacing it with a wooden fence.(ie. the ground current flow was still going to this pool):)
 

iwire

Moderator
Staff member
Location
Massachusetts
ghostbuster said:
We then isolated the primary neutral from the secondary neutral with all the necesaary inspection approvals.Problem solved.:)

How is that even possible, both are grounded systems?
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
You can never have complete isolation between primary and secondary, because both are connected to Earth via grounding electrodes.

But apparently removing the metallic connection between the primary ground system and the secondary grounded conductor provides sufficient impedance between the two that 'stray voltage' problems are often resolved.

-Jon
 

iwire

Moderator
Staff member
Location
Massachusetts
winnie said:
But apparently removing the metallic connection between the primary ground system and the secondary grounded conductor provides sufficient impedance between the two that 'stray voltage' problems are often resolved.

Jon, I don't see how that is possible under the NEC.:-?

Both the primary neutral and the secondary neutral will be directly connected.:smile:
 
It was mentioned in an earlier post how the metal fence many feet away was causing some shocks and how they replaced the fence with a wooden fence.

I had a similar experience a couple of years ago, only not with a pool. The fence around the property was replaced with a wooden fence. About 20 years after the fence was replaced (there were multiple buildings on the property) a few of the buildings caught fire and in one of the buildings the service was glowing red. Also one of the other buildings, the water pipe to the laundry was also glowing red. They found a break in the underground supply to the one building and had to dig and replace the entire supply.
 

radiopet

Senior Member
Location
Spotsylvania, VA
Pierre C Belarge said:
It was mentioned in an earlier post how the metal fence many feet away was causing some shocks and how they replaced the fence with a wooden fence.

I had a similar experience a couple of years ago, only not with a pool. The fence around the property was replaced with a wooden fence. About 20 years after the fence was replaced (there were multiple buildings on the property) a few of the buildings caught fire and in one of the buildings the service was glowing red. Also one of the other buildings, the water pipe to the laundry was also glowing red. They found a break in the underground supply to the one building and had to dig and replace the entire supply.
Yikes......sounds like a NASTY situation...
 
iwire said:
Jon, I don't see how that is possible under the NEC.:-?

Both the primary neutral and the secondary neutral will be directly connected.:smile:
I believe an isolation transformer would do this. Both neutrals would be tid to ground, but not directly to each other.
 
I don?t know your local rules where you?re at?

But if you pull the meter and then you still have power flow on the neutral then it?s up to the POCO to fix it. It sounds like it?s not coming off of the property your working on it?s a problem that somewhere else.

Then the bad part is getting the POCO out to prove it?s there fault and not your fault.
I can think of a lot of ways to get DC voltage this way but only a few for AC voltage.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
John,
I believe an isolation transformer would do this. Both neutrals would be tid to ground, but not directly to each other.
Not really....there will still be a direct connection. The primary EGC must be bonded to the transformer case/frame and the secondary neutral will also be bonded to the transformer.
Don
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Bob,
Jon, I don't see how that is possible under the NEC.:confused:
Both the primary neutral and the secondary neutral will be directly connected.:smile:
I believe that the isolator is installed on the line side of the service equipment placing it outside of the scope of the NEC.
Don
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
iwire said:
Jon, I don't see how that is possible under the NEC.:-?

Both the primary neutral and the secondary neutral will be directly connected.:smile:

Removing the metallic bond between primary earth/neutral and secondary is an explicit violation of the NEC.

The NEC doesn't apply to the transformers in question, but from what I've read, it is also a fight to get the POCO to make this separation.

My opinion is that separating primary and secondary neutral will probably help with some forms of 'stray voltage', but that this is a band-aid that masks a core design issue, and one that will introduce risks of its own. I don't have any serious engineering study or field work to back up my opinion, however :)

-Jon
 
The concept of seperatly derived systems seems a bit fuzzy to me. There seems to be a fine line as to when a transformer is used on a machine to isolate the hot and neutral from the building power and both are left floating(from the macufacturer) and when it is a seperatly derived system and therfore the neutral is bonded.
 
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