5 volts between pool and patio

[just engineering]

Hello - new to this forum and would appreciate any help on thie NEV problem. Heres the scoop - I am working for an electric utility trying to resolve a shock complaint at a pool in a newer residential neighborhood. Suffice to say that all utility and customer equipment has been checked and all is ok. We installed a neutral blocker in the padmount transformer and it did not reduce the NEV. The transf feeds 3 other homes. A cable and phone pedestal is located at the utility transformer, we ensured that their grounds went to the primary ground only. The problem I believe lies in the fact that the CATV is grounded at each customer's service and that in a roundabout way bypasses the neutral blocker.

Is there a "blocker" for catv that can be used either at the customer service entrance or at the catv pedestal that would eliminate the ground loop during steady state conditions yet conduct during a fault or lightning?

Thanks

 

[Dennis Alwon]

If you disconnect the power to the residence in question does the voltage disappear???

 

[SG-1]

If you disconnect the catv does the voltage go away ? If so, then Radio Shack carries such a device. It is two balm transformers wired back to back.

 

[mcclary's electrical]

Welcome to the forum. When you say "customer equipment has been checked",,,what does that mean? who? checked what? pool bonding? equipotential bonding grid? slab bonding? pool panel? seperate structure GES? please give more details

 

[don_resqcapt19]

What type of cable is used for the primary feed to the padmount?
Exactly how and where are you measuring the neutral to earth voltage.

 

[ghostbuster]

I would suggest you read the article on page 6 of this magazine,as well as the link in the article to the utility being fined for several lake electrocuton deaths due to faulty utility wiring.It sounds like you are trying to "bandaid the problem" rather then find the root cause.You may find yourself in court.

Please,please go and find the real underlying problem before someone else gets hurt or killed.

http://www.ebmag.com/images/stories/PDFarchive/2009/12ebdecjan20092010bluebook.pdf

 

[George Stolz]

Before you buy more gadgets, I'd manually remove all outside points from the house and see when the voltage disappears.

 

[gar]

100529-0707 EST

just engineering:

If you are working on this problem this weekend, then I will take some time to outline some tests you need to make. But I have a time limited project I need to be working on and I would prefer to delay comments to you. But as pointed out above you may have a very serious problem.

.

 

[brian john]

Hello - Suffice to say that all utility and customer equipment has been checked and all is ok.
Thanks

Actually I would think you must have missed some stuff. Not trying to be sarcastic but when you find the issue you will have checked all the equipment.

If a residential electrician looked into this I might try someone more in depth onto PQ issues like the local electrical testing company.

Some stuff below has been noted above.

Did you shut off power to this house.
Did you shut off power to houses in the area.
Are the houses on a common transformer?
Are the houses on a common metallic utility water pipe or gas system?
Did they do neutral zero sequence readings on the panel?
Did they measure current on the GEC, MBJ, and any metallic piping systems in the house and between houses?
Did the measure current on the GEC at the transformer?
Did they measure for current at the pool equipment?

 

[dbuckley]

If the complaint is that there is 5V between the pool (water presumably) and the patio (what - metalwork? recepticals? concrete? pool ladder?) then there is a failue to have the area adequately equipotentially bonded. It doesn't matter - much - what the actual potential between the pool and elsewhere is, as long as the pool and surrounds are bonded so they are at the same voltage, thus no tingles.

This could be a very nasty (and expensive) problem to solve. But neutral blocking isn't the answer.

 

[just engineering]

more info

more info

Thanks all - more detail.
1. Customer meter removed voltage still there
2. Transformer deenergized (4 customers total), voltage still there
3. Customer's service neutral removed from secondary connector at transf - voltage goes away. (all 4 meters were removed)
4. With neutral back in and all catv disconnected voltage goes away.
5. Neutral blocker installed - no change
6. The pump, filter, and salt water control are not double insulated, so they must be connected to the bonding grid. However when we remove the bonding system grounds from all, the voltage goes away. Meaning that the bonding system ties to the grounding system through the equipment. This equipment is 20' off the pool - it would be nice just to leave the bonding grid ground off, but that goes against the code (since the equip is not double insulated)
7. This is a joint trench subdivision meaning that electric primary, secondary, catv, phone, and gas are all in the same trench (albeit at different elevations)

My thoughts- the problem is on the utility, more precisely with the primary neutral. Because CATV is grounded (to a driven ground as is the secondary neutral) at each service entrance you are essentially bypassing the neutral blocker. It seems we need to separate the grounding with catv which is not easy to do. Later today meeting on site with power company and catv personnel.

Paul

 

[just engineering]

more questions answered/asked

more questions answered/asked

More detail -
1. the voltage is measured between the pool water and the concrete patio with both a fluke and analog meter.
2. The pool contractor said he bonded the reinforcing mesh with a #8 Cu ground wire and brought that out to the pool equipment. The way I read it this satisfies the NEC.
3. We drove 4 ground rods (2' deep or so) connected them together with Cu wire in a loop above grade around the pool and connected to the bonding system. No change in voltage.

As stated earlier - when the bonding system is not connected to the equipment grounding system the voltage goes away. Since the pool equipment is 20' away from the pool what would the harm be in simply disconnecting it from the bonding system? It seems less safe with it connected than disconnected (even if it is not double insulated)

 

[George Stolz]

3. Customer's service neutral removed from secondary connector at transf - voltage goes away. (all 4 meters were removed)
4. With neutral back in and all catv disconnected voltage goes away.

That doesn't make any sense. Is the voltage consistent when everything is hooked up, or does it vary? What I'm getting at is, are you absolutely sure that the voltage does not go away on it's own from time to time?

 

[just engineering]

George - not sure what you are referring to that doesn't make sense. separating the service neutral from the others off that transformer removes the stray voltage from the pool. reconnecting it to the others it comes back. The voltage at midday is around 2 volts (steady), at the peak around 6 o'clock it is around 5 volts.

 

[George Stolz]

On number 3 you state that removing the neutral eliminates the voltage.

On number 4 you stated that when the neutral is reconnected the voltage can be eliminated be removing the CATV.

These two actions/results conflict, it doesn't make sense.

 

[Smart $]

... Since the pool equipment is 20' away from the pool what would the harm be in simply disconnecting it from the bonding system? It seems less safe with it connected than disconnected (even if it is not double insulated)

You still need to find the problem rather than patching it. If this voltage is a result of utility neutral fault, the problem may effect others in the area as circumstances change. You need to measure current wherever you get voltage when system is deenergized. You need to know the current path before a proper assessment can be made.

 

[brian john]

More detail -
1. the voltage is measured between the pool water and the concrete patio with both a fluke and analog meter.

Will this light a 6 volt bulb?
Did you try this with low impedance meter?
Can we feel 6 volts?

2. The pool contractor said he bonded the reinforcing mesh with a #8 Cu ground wire and brought that out to the pool equipment. The way I read it this satisfies the NEC.
3. We drove 4 ground rods (2' deep or so) connected them together with Cu wire in a loop above grade around the pool and connected to the bonding system. No change in voltage.

As stated earlier - when the bonding system is not connected to the equipment grounding system the voltage goes away. Since the pool equipment is 20' away from the pool what would the harm be in simply disconnecting it from the bonding system? It seems less safe with it connected than disconnected (even if it is not double insulated)

MAJOR LIBILITY

 

[Dennis Alwon]

Sounds to me like the voltage may be travelling thru another customers grounding system.

 

[zbang]

Wild idea- since a padmount is mentioned, I'll assume an underground service. Is the underground neutral insulated (I'll assume it is)? Does it run anywhere near the pool? Could the insulation be compromised? Did a ground rod contact the conductor? That wouldn't show up as sparks, but would cause all kinds of interesting but less visable things. Since you're working with everybody involved, I'd disconnect the service lateral at both ends and look for continuity between the neutral and anything else metalic (ground rod(s), water pipes, etc). I'd also megger the lateral between the conductors and a test ground rod.

 

[don_resqcapt19]

It sounds like this transformer is fed line to neutral on the primary side and that there is an issue with the concentric neutral on the high voltage primary feeder. This is not an uncommon issue, especially with older primary cable were the concentric neutral was not jacketed.