5 volts between pool and patio

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A Balun transformer for the catv should make the voltage go away at the pool. I actually spelled it correctly this time ! As stated before this is a patch and will not fix the real problem in the neighborhood.

You need to pull the meters on each of the other houses one at a time to see if the voltage at the pool goes away.
 
Ok, the tests confirm this is a ground-to-ground problem, as I like to refer to them. We've finished playing with hots and switching things on and off.

Based on the answers above, it appears that the patio concrete is at a different potential to the house electrical ground (from the N/G bond) which is equipotential with the pool. This is becuase when you disconnect the pool bond the problem goes away. What actually is happening is that the pool adopts the potential of the surrounding soil, which is the same potential the patio is at.

You can confirm this with an extension cable; measure between the ground pin of an extension cable plugged into a house socket, to the patio, and also to the pool. I expect you'll find the patio is 5V up and the pool is at or near zero volts to house ground.

Assuming this is the case, then the patio is not equipotential with the pool. This is not good, and the only proper fix is to extend the equipotential bonding to include the patio, and that requires a different set of tradesman, and a big bill for the customer.

You could try and map the non-equipotentialness; get your boots and socks off, grab one meter probe, with the other probe still connected to house ground through the extension lead, wander round the surrounding concrete and grass watching the meter. You may locate where the stray current is being injected... And that may lead to an acceptable fix.
 
dbuckley - I think you are correct. The current is coming from normal current sharing on the primary neutral through a multi-point grounded electric system. With long, heavily loaded, single phase (7200V) lines a certain amount of current travels through the ground.

It seems another accepetable fix is to separate the secondary and primary neutrals - from all grounded sources including catv. At the transformer there may be 6 volts between primary and secondary neutral but with a neutral blocker installed it should be safe during faults or lightning events. By connecting the bonding system to essentially the primary neutral through normal connection at the service entrance (and transformer when normally connected) we are placing voltage on the entire grounding/bonding system. I agree that the pool/patio is not sufficiently bonded, but it appears it meets the NEC (the electrical inspector passed it), it just isn't good enough. So if we can remove/reduce the voltage by seperation of the primary/secondary neutrals I think we can resolve the problem. Going out again today.

Thanks everyone for their input. I'll let you know..
 
Do Not Leave Us Hanging

Do Not Leave Us Hanging

There are two excelent thoughts just posted regarding you issue., PLEASE let us know the outcome of this and if either of these ideas and the fixes required panned out.
 
just engineering said:
dbuckley - I think you are correct. The current is coming from normal current sharing on the primary neutral through a multi-point grounded electric system. With long, heavily loaded, single phase (7200V) lines a certain amount of current travels through the ground.

It seems another acceptable fix is to separate the secondary and primary neutrals - from all grounded sources including catv. At the transformer there may be 6 volts between primary and secondary neutral but with a neutral blocker installed it should be safe during faults or lightning events. By connecting the bonding system to essentially the primary neutral through normal connection at the service entrance (and transformer when normally connected) we are placing voltage on the entire grounding/bonding system. I agree that the pool/patio is not sufficiently bonded, but it appears it meets the NEC (the electrical inspector passed it), it just isn't good enough. So if we can remove/reduce the voltage by seperation of the primary/secondary neutrals I think we can resolve the problem. Going out again today.

Thanks everyone for their input. I'll let you know..
Click to expand...

While the voltage drop on the main grounding neutral on the primary can be part of the problem, if there is a voltage drop on the service neutral it will also cause this problem, so the answer can be two fold, if you do separate the primary/ secondary neutrals and the cable, and the problem doesn't go away, then it might be worth while to run a separate grounding conductor also to the transformer, and then keep all grounding and neutrals separate at the dwelling service, this Will stop the voltage drop of the service neutral from showing up as a difference of potential at the pool to earth, and since this new grounding conductor will not have current on it, there will be no voltage difference at the pool, the only draw back is if the meter can has a permanently bonded neutral.
Remember the thread about a tech requiring that there be no more then .5 volts different between the EGC and neutral, this is the same kind of problem. I have delt with this very same thing but with a marina, and had a heck of a time to get the state to allow a delta to delta isolation to the service, and seperate grounding conductor from the transformer but in the end it worked just fine, no more shock on boats and ruined metal hulls.
 
how we left it

how we left it

We confirmed through testing that the pool water is bonded to the service ground. Also the deck is at a different potential, hence the tingle. The pool man went at length to discuss the rebar arrangement and the grounding to the equipment (and therefore the service ground); however, the voltage remained. In the end we advised the homeowner that the utility had done all it could and that the deck must be better bonded to the service ground. They are working to install a grounding system around the pool and connect it to the rebar - hope it works.

One note about the neutral blocker. It will work. However, the coaxial catv network cannot isolate the grounds. Their feeder throughout the neighborhood is connected at every utility transformer ground. And at every service entrance off the transformer in question it is grounded to the secondary grounding system. In effect it bypasses the blocker at each service entrance. Their engineer told me that they cannot isolate the ground at risk of ruining the signal.
 
another thought

another thought

What if we installed the blocker between the deck equipotential bonding conductor and the pool equipment grounding conductor. The voltage does indeed go away but I guess would open up to tingle a repairman working on the equipment.

All in all that might be a decent option if the local electrical inspector would go for it.
 
This has been a big problem for pools and dairy farms, there are quite a few papers on Mikes site that go into detail about this problem, I have some disagreements on some things but for the most part they do give a good detail of the problem at hand, look in the newsletter archive area for them.

What I disagree with is where they claim current passing through earth is causing this voltage to appear on grounding that is also bonded to the multi-grounded neutral system, in my testing I can not find where this could be true, but the voltage drop on the MGN or service neutral will in fact cause this problem, and in all cases I have wittiness, this has been the case, if isolating the grounding from the service drop results in the voltage going away then this is the case and further testing should be done to see which it is, the MGN or the service drop, if it turns out to be the MGN then suspect that there might be a bad connection in this MGN back to the substation, and the transformer loads are using purely the earth as a return path to the substation, if the POCO will use a amp meter on the MGN and follow the path back they will find the point where the MGN has no current anymore, the next connection after this point is the bad one and should be replaced, I have found a few of these just by measuring the current on the grounding conductor that runs down each pole, and as soon as I get to the one that has no current on it, then I direct the POCO to replace the crimps after this pole, each time it solved the problem, but if it is a case of undersized MGN then your fighting a whole new battle, as this will require wire replacement and it would be hard to get them to budge.
The above is only for a unbalanced Wye grid system, a delta would not have this problem but can have a secondary loss of neutral several poles down but back feed the return path through a common water system to your service, which can cause the same symptoms.
Each has to be delt with on a case by case bases.
 
To add to this, (got called out earlier)

If you turn off the main to the premises and the stray voltage goes away, then it is a neutral voltage drop problem in the service drop or laterals, if the voltage remains then it is a MGN problem, of course this is if you confirm isolating the grounding from the service which confirms one or the other above.

One case we had about 3-5 volts that varied with current use in the house, turning off the main removed the voltage, running a wire from the pole ground to the house and testing the voltage gave us the same voltage drop, so POCO up sized the laterals 3 sizes and the problem was eliminated, in another case turning off the main didn't remove the voltage, running current test on the pole grounding toward the substation resulted in a loss MGN connection 4 poles down, new crimps fixed the problem, but there was one that will throw you, and it involves loosing the primary neutral to the serving transformer, this will cause a much higher voltage to appear on all the grounding of the building, we had 35-56 volts and it will also go away when the load is removed, so current test on the primary neutral is the only method I know to confirm this one, and can be very dangerous since the voltage can get as high as the primary voltage if you start un hooking grounds, so be careful with this one.
Hope this helps with stray current understanding;)
 
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hurk27 said:
To add to this, (got called out earlier)

If you turn off the main to the premises and the stray voltage goes away, then it is a neutral voltage drop problem in the service drop or laterals, if the voltage remains then it is a MGN problem, of course this is if you confirm isolating the grounding from the service which confirms one or the other above.

One case we had about 3-5 volts that varied with current use in the house, turning off the main removed the voltage, running a wire from the pole ground to the house and testing the voltage gave us the same voltage drop, so POCO up sized the laterals 3 sizes and the problem was eliminated, in another case turning off the main didn't remove the voltage, running current test on the pole grounding toward the substation resulted in a loss MGN connection 4 poles down, new crimps fixed the problem, but there was one that will throw you, and it involves loosing the primary neutral to the serving transformer, this will cause a much higher voltage to appear on all the grounding of the building, we had 35-56 volts and it will also go away when the load is removed, so current test on the primary neutral is the only method I know to confirm this one, and can be very dangerous since the voltage can get as high as the primary voltage if you start un hooking grounds, so be careful with this one.
Hope this helps with stray current understanding;)
Click to expand...

We had one long ago...48 volts between a bathtub faucet and the drain...bad neutral in the POCO xmfr.
 
Seen this before.

Seen this before.

We've seen this before. The first time was for the guy who does the vinyl on our vans, so we went flying over en-mass when we heard his 3 year old and wife got "shocked" on a pool we had just finished. We jumped through all the same disconnect and isolate hoops right down to the utility physically disconnecting the conductors at the pad, More times than not we are called out to put the ground resistance tester on, do a fall of potential and verify the continuity of the bonding system. The last 3 times the same engineer for the utility has come out and the two of us have walked the utility line back to the lightning arrestor. A blown lightning arrestor can ground the utility power and it will track for, I'm not kidding here, miles. This particular one was 1.4 miles away. I watched them set up to replace the lightning arrestor, and then while we were simultaneously reading the voltage on each of our meters at the pool, they put the new one in. It fixed the problem immediately. The engineers response "This is becoming a real problem for us as a utility. The better the requirements for swimming pool grounding, the more they seem to attract transients. I know very little about transmission power or how it's done. Only what I have learned from the guys at utility, so I don't know how the lightning arrestor works, just what they explained. This fixed the problem, so let them know what we found, and they can take a look.
 
I've had a problem with my electrical ground and CATV ground being at a different level causing current to travel between CATV line and TV(frame bonded to outlet ground) causing stripes to appear on screen. I lifted the TV's ground and it went away.

Just for kicks, when you clamp the cable TV service entry cable with a clamp meter, do you get any readings?
 
krisinjersey said:
We've seen this before. The first time was for the guy who does the vinyl on our vans, so we went flying over en-mass when we heard his 3 year old and wife got "shocked" on a pool we had just finished. We jumped through all the same disconnect and isolate hoops right down to the utility physically disconnecting the conductors at the pad, More times than not we are called out to put the ground resistance tester on, do a fall of potential and verify the continuity of the bonding system. The last 3 times the same engineer for the utility has come out and the two of us have walked the utility line back to the lightning arrestor. A blown lightning arrestor can ground the utility power and it will track for, I'm not kidding here, miles. This particular one was 1.4 miles away. I watched them set up to replace the lightning arrestor, and then while we were simultaneously reading the voltage on each of our meters at the pool, they put the new one in. It fixed the problem immediately. The engineers response "This is becoming a real problem for us as a utility. The better the requirements for swimming pool grounding, the more they seem to attract transients. I know very little about transmission power or how it's done. Only what I have learned from the guys at utility, so I don't know how the lightning arrestor works, just what they explained. This fixed the problem, so let them know what we found, and they can take a look.
Click to expand...

Our post #6 details a similar situation where the community swimming pool grounding was "attracting" this utility current.The better the pool ground,the higher is the utility current flowing into the pool ground system.:mad:
 
So now what?

So now what?

If we just created a transient voltage "magnet" how do we fix the problem? By ensuring we don't have one problem we are creating another, and one that we don't have the ability to repair. So do we put into the contract "Swimming pool bonding grids, when properly installed to meet the current requirements of the NEC, may increase the occurance of electric shock do to poorly maintained electric utility systems. This problem, and it's associated repair, is not included in this contract." That'll go over great I'm sure.
 
ghostbuster said:
Our post #6 details a similar situation where the community swimming pool grounding was "attracting" this utility current.The better the pool ground,the higher is the utility current flowing into the pool ground system.:mad:
Click to expand...

krisinjersey said:
If we just created a transient voltage "magnet" how do we fix the problem? By ensuring we don't have one problem we are creating another, and one that we don't have the ability to repair. So do we put into the contract "Swimming pool bonding grids, when properly installed to meet the current requirements of the NEC, may increase the occurrence of electric shock do to poorly maintained electric utility systems. This problem, and it's associated repair, is not included in this contract." That'll go over great I'm sure.
Click to expand...

Both of you guys are not understanding the relationship between a voltage drop in a service neutral or MGN and grounding to Earth. well I could write a book on this, but I will try to make it a short one.

first of all a good earth grounding does not really "attract this utility current" nor is it a magnet for the same, while yes it does allow more current to flow, but it also reduces the voltage level by lowering the resistance in the neutral between the service and transformer or between the transformer and the substation in the case of the MGN.
We must understand, that when there is a voltage drop in a grounded conductor such as the service neutral or MGN, this voltage drop doesn't result in the Earth reference voltage rising(so we can dispel with the myth that there is voltage on the Earth), it is because the neutral voltage reference to Earth has raised above the X/0 0 volt reference point that you would have at the transformer so in reality we have a voltage on the grounding, neutral, MGN, You can prove this by running a long wire back to the grounding that comes down the pole the transformer in on and measure the voltage between the pole grounding conductor and the service grounding, this will be the voltage raised up from Earth, it is a result of the resistance loss in the neutral conductor, so if we look at this in a reverse view, starting at the pool end, a better Earth ground connection would lower this voltage, but don't get this wrong as the amount of an earth connection that would be required to totally bring down this small voltage would be far beyond most simple pool bonding systems, in fact a bond to Earth is not the intended effect for equal potential bonding, it has nothing to do with a connection to Earth, it is only to bring all things to the same potential, unfortunately there is always an edge to this area that will have a voltage difference, we hope the installers have this edge far from the waters edge so people in the water can't feel this voltage, but as we see it doesn't always get done, as we can see in the OP the concrete deck is not bonded to the EPBG, another way to prevent an edge to a protected area, is to fade the voltage potential off as you reach the edge, this is done by sloping the bonding grid deeper as you reach the edge, this allows for a more slower gradient voltage drop off as you reach this edge, this is done in many sub stations.

so a basic summery is:
The reference of the Grounding around the pool is raised above what it should be.
The effect of the EPBG to earth is just a side effect, not the intent of the NEC,
To remove this voltage, the VD problem must be addressed or a code compliant method of isolation of the service neutral/MGN from the premise grounding would have to be done.
 
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Awesome

Awesome

That could be the single best explanation I have ever gotten about anything, ever. I totally get it, and in a completely different way now. Having said that, is this something that should be addressed by the code in the next update cycle?
 
krisinjersey said:
That could be the single best explanation I have ever gotten about anything, ever. I totally get it, and in a completely different way now. Having said that, is this something that should be addressed by the code in the next update cycle?
Click to expand...

that is the other problem.

most of this problem is from the utility side of the service, and can't be address in the NEC, and getting the utility's to change their ways is something that doesn't happen easily if ever at all!

remember they have the POWER:mad:
 
but I should add that there has been discussions on the matter and there are devices that would effectively isolate the pool EPBG from the service grounding/neutral, one of them I brought up was the use of MOV's between the pump, and the pump EGC, or any circuit EGC that would bond the EPBG back to the service, the metal Oxide Varistor rated at about 130-150 volt's would provide a fault current path if the current ratting of it was high enough, and had a low leakage current, but when there is no fault it would act like an open circuit, a lower voltage/current rated version would be effective if the pool equipment had GFCI protection also, but code as of now doesn't require it for hard wired equipment. so yes there is other methods that could be effective that the NEC/UL could adopt.

But like AFCI's and GFCI's designing, testing, UL listing, manufactureing, would be years down the road even if they were to start it today.
 
krisinjersey said:
Having said that, is this something that should be addressed by the code in the next update cycle?
Click to expand...
There is a varioation of this problem that could be addresserd by code, which is the issue of marina docks and folks in the water getting shocks. This issue could be addressed by permitting SDSs not to require the secondary being bonded to the supply ground, but allow it to float. This needs a local ground rod and RCD protection, but provides a (in the absence of a fault) a safe shock-free environment, which the existing requirements do not.
 
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