Stray voltages between concrete deck and pool

[oilengineer]

Split to new topic - MikeInTN - Moderator

We recently installed a 40x16 fiberglass in-ground pool w/ 8' concrete decking. The problem is that the concrete has approximately 2 volts and when one has wet feet on the concrete and touches the pool water, a tingling or slight shock occurs. The kids notice it more than the adults. We've had the power company and phone company out and everything checks out as far as good grounds, etc. When the primary power is killed, the voltage actually increases to 3 volts at the pool. The pump wiring has been checked and rechecked and the only electricity going to the pool is the light and it is well grounded. The power company thinks it may be an induction current from a nearby cell phone tower. Does anyone have any other ideas? Thanks.

 

[dschlic1]

I believe that the code (NEC) requires a ground mesh around all pools. This usually consists of copper wire in a square pattern similar to the iron wire square grid used to reinforce concrete. This copper grid is then connected to the electrical system ground. I suggest looking into this aspect.

 

[Guest]

Static electricity? Dissimiliar metals causing a current to flow between the materials?

Since it is so low it sounds like when of these kind of currents versus a try live wire issue.

 

[JohnT]

It is stray voltage. There should have been a bonded mesh under and around the pool or the rebar in the concrete should have been connected to the bonding system, depending on what version of the NEC your locality has adopted. It's likely that the ladder sockets and light housing are bonded, but it's pretty common for electricians to leave the deck unbonded, mostly because they don't understand the requirements in Article 680.2 of the NEC. It's also very common for an unbonded deck to shock people like you are describing.

You have two problems: First is stray voltage, which is because of either the poor grounding practices of your power utility or a defective piece of electrical equipment near your home. Well pumps are a common source. Second is an imroperly bonded pool. The bonding system is supposed to protect you not only from small nuisance level voltages, but also from lethal voltages such as might occur if a powerline fell near your home or a piece of construction or farm equipment shorted a powerline to the earth.

 

[oilengineer]

Thanks for the responses. I'll check again w/ the pool contractor to make sure the pool was bonded correctly and that he used rebar in the concrete. Our pool has no ladder, just the light. The pool contractor has 25 years experience and has a good reputation and does good work. However, that doesn't mean he didn't cut corners on my pool.

 

[cobra46]

The bonding requirement that JohnT described is a fairly new requirement so regardless of experience your PB may not know about it if your municipality doesn't require it. Someone correct me if I'm wrong but I think is was first adopted in the 2005 NEC which is updated every three years.

Although concrete is normally a non-conducting material, wet concrete, as you've seen first hand, can conduct electricity. The bonding requirement is to ensure that the pool water and all concrete within three feet of the water is at the same potential (voltage). This helps prevent you from getting zapped when something goes wrong.

Did you take any photos during construction? Did you have to have a 'pre-deck inspection'? The primary purpose of this inspection is to verify the deck bonding is done correctly.

 

[Guest]

How do you know it is 2 or 3 volts?

Using a voltmeter?

Is it AC or DC if you are measuring it with a meter?

If AC then it must be coming from an problem electric device.

 

[duraleigh]

oilengineer,

Welcome to the forum.

I am not qualified to speak on bonding but JohnT is. Stray voltage around the pool cam be a pretty serious issue and, if it were my pool, I would pursue it until it's fixed.

From reading over the years on this and other forums, the electricians address stray voltage as avery serious issue.

I believe if you contact the legal department of the utilities and mention liability to them they may become very responsive to your continued requests. I believe in fighting my own battles but your issue would be completely beyond my capability to resolve and the utilities have the expertise to resolve it.

 

[PoolOwnerNumber9]

I know of several pools that have a similar problem where the homeowners have never been able to figure out where the stray current was coming from or how to prevent it. I know that it can be very annoying, and can cause you to be concerned for your and your kid's safety. I would encourage you to do your best to find and correct the problem.

A few questions:

1) How did you measure the voltage?
2) From where to where?
3) As AC or DC?
4) If DC, what was the polarity? Did the electricity flow from the pool to the deck or from the deck to the pool?
5) Is there a SWCG (Salt Water Chlorine Generator)?

 

[oilengineer]

To Pool Owner Number9:

1. Voltmeter - my dad's, phone company and power company
2. Pool water to concrete. However, the earth also has voltage.
3. AC, but not totally sure.
4. ???
5. Yes

The power company is supposed to come back Monday and check my neighbor's pool across the road and check my neighbor that is closest to the cell phone tower. Moreover, the power company has a substation only 1500' or so from our house. I'm wondering if it has been checked lately for proper grounding?

 

[PoolOwnerNumber9]

(4) If the current is DC, there will be a polarity, like on a battery, positive and negative. When you test with the voltmeter set to DC there will be a positive or negative indicator on the display. If you reverse the leads then the polarity will reverse. Although convention says that electricity flows from the positive (+) terminal of a battery to the negative (-) terminal of the battery, in reality electrons flow from negative to positive. If you put the red lead on the (+) terminal of a battery and the black lead on (-) the terminal, then the reading will be positive. If you switch the leads it will be negative. This can tell you the direction of the current flow. If the electricity is measured in AC then there is no direction. AC switches direction 60 times a second (60 Hz) for common house current.

(5)The salt water increases the conductivity of the water. It does not cause the problem, but it does increase the electricity's ability to flow, which makes the shock more noticeable. It increases the current flow (amperage) at the same voltage. In an electrolyte, such as salt water, the positive ions (cations), such as sodium, carry positive charge in one direction, while electrons and negative ions (anions), such as chloride ions, carry negative charge in the opposite direction.

You should also do a current (amperage) test to determine the capacity of the electricity to flow. The current flow rate is as important as the voltage in determining the danger. Most likely this will be in the 1 to 3 milliamp range. You can determine the power by multiplying the voltage by the current.

One common source of stray currents is caused by insufficient return capacity to the electrical substation. If there is insufficient neutral wiring back to the substation the electricity will use the earth to return to the substation. The closer you are to the substation the larger the currents will be as they converge on the station.

Local businesses that use high power or capacitors that store and release large bursts of electricity can overpower the neutrals and send current into the ground. The cell tower is possibly a contributor to the problem. Are you between the cell tower and the substation?

If there are any businesses nearby that use "Impressed Current Cathodic Protection" that could contribute to the problem. ICCP is used for storage tanks, pipelines etc. ICCP uses DC voltage to prevent corrosion in metal structures.

Ask the PB if the electrical work fully complies with the NEC code article 680. Ask for a certificate of compliance from a licensed electrician.

What inspection and certification is required in your area? Were all inspections done and certifications issued?

 

[oilengineer]

Our house sits between the cell tower and the electrical substation. There is not a nearby business except a church. We are outside the city limits so there are no inspections that I know of. It was the same when we built the house. I spoke w/ the PC at length yesterday and he also mentioned the PC's neutral as the most likely source for the problem. The only other FG pool that he had a problem similar to mine was his own and it ended up being the neutral wire in the motor. He was getting slightly shocked at the pool and in his pool house. He did my pool like the hundreds of other FG pools he does (including two friends of ours in the last year). The light is grounded but he used no rebar in the concrete.

I'll ask the PC to check the substation. They have made 5 trips out so far trying to diagnose the problem including checking all the house and motor wiring. I've been pleased w/ their concern.

 

[PoolOwnerNumber9]

I am concerned that there were apparently no inspections of any kind done. Even though you are outside the city limits I find it hard to believe that you would not still be under the jurisdiction of the state or county. I would want all aspects of the electrical system, including the grounding and bonding, to fully comply with the NEC and local codes. The concrete definitely should have had either wire mesh or rebar for strength and for creating an equipotential bonding grid.

I am not sure how much time, effort and money you are willing to spend on this or how serious you think this is so I will just make suggestions and you can decide what is worthwhile and what isn't.

1) Set up a voltage and current monitoring and recording device that can record over an extended period of time of about 14 days. Ask the people at the electrical substation to give you a 14 day recording of their power output that you can use to compare to your recordings to see if there is any significant correlation. Ask the cell tower owners to also give you power usage readings for the same period for you to use in your comparison. Ask them if they use any electrical storage devices like batteries or capacitors. Ask them if they use any Impressed Current Cathodic Protection. This may take a civil suit and a subpoena if they are not willing to cooperate.

2) Ask the substation how much power returns to them via the ground and how much returns on the wiring.

3) If there is a substantial amount of current returning to them via the ground they may need to upgrade their wiring to eliminate the problem. They will probably not be too excited to do that as it would be very expensive.

4) If the pool builder does not resolve this fairly quickly, I would consider hiring an electrician to thoroughly check your electrical system for whatever is causing this.

 

[Guest]

I am concerned that there were apparently no inspections of any kind done. Even though you are outside the city limits I find it hard to believe that you would not still be under the jurisdiction of the state or county. I would want all aspects of the electrical system, including the grounding and bonding, to fully comply with the NEC and local codes. The concrete definitely should have had either wire mesh or rebar for strength and for creating an equipotential bonding grid.

I am not sure how much time, effort and money you are willing to spend on this or how serious you think this is so I will just make suggestions and you can decide what is worthwhile and what isn't.

1) Set up a voltage and current monitoring and recording device that can record over an extended period of time of about 14 days. Ask the people at the electrical substation to give you a 14 day recording of their power output that you can use to compare to your recordings to see if there is any significant correlation. Ask the cell tower owners to also give you power usage readings for the same period for you to use in your comparison. Ask them if they use any electrical storage devices like batteries or capacitors. Ask them if they use any Impressed Current Cathodic Protection. This may take a civil suit and a subpoena if they are not willing to cooperate.

2) Ask the substation how much power returns to them via the ground and how much returns on the wiring.

3) If there is a substantial amount of current returning to them via the ground they may need to upgrade their wiring to eliminate the problem. They will probably not be too excited to do that as it would be very expensive.

4) If the pool builder does not resolve this fairly quickly, I would consider hiring an electrician to thoroughly check your electrical system for whatever is causing this.

Even outside of cities you still have the county that inspects. Most states have this.

 

[JohnT]

Even outside of cities you still have the county that inspects. Most states have this.

Most rural areas in the US have no building code, no zoning and no permit or inspection process for anything. I built my house, two barns, the poolhouse and the pool, and the only thing I had to get approved was a soil survey for the septic system install

 

[oilengineer]

Thanks so much for the suggestions. Fortunately, we will winterize our pool within two weeks as we live in southern Illinois. This will give us plenty of time to diagnose the problem and fix it. On hindsight, I would have done things differently especially concerning the wire mesh (he used fiber mesh) or rebar in the concrete. I'm convinced the wiring in our house and pool are Code and are not the source of the problem. As mentioned, we've had several friends put in pools within the last two years, both in and out of the city limits, and the procedures followed by the PC were the same as ours.

I'll continue to dog the electric company to trace down the problem. After reading the posts and googling stray voltage, I'm convinced it's their problem either at the substation or the transformer, which sits 200' from the pool between my neighbor and me. When the primary was turned off, my neighbor had a stray voltage reading too outside his house.

 

[oilengineer]

One other thought: when the pool contractor comes back to install our winter cover, will the metal (I'm assuming their metal) anchors help in creating no potential difference between the pool water and the concrete? Or, while he is installing the cover, is there anything he can do w/ the concrete to help the problem? Obviously it won't solve the stray current problem, but it may lessen the problem at the pool.

 

[Guest]

Even outside of cities you still have the county that inspects. Most states have this.

Most rural areas in the US have no building code, no zoning and no permit or inspection process for anything. I built my house, two barns, the poolhouse and the pool, and the only thing I had to get approved was a soil survey for the septic system install

Scary! Some regulation, such as electrical inspections, keep us safe from unsafe electrical installations.

Did you need a COO (certificate of occupancy) for your house?

Is it that they don't require it or someone just forgot to tell them? Usually when you apply for the building permit they set a flag for the inspectors. Did you file a building permit?

Also, my utility company required an inspection before placing the meter to ensure the wiring beyond the meter was code.

 

[JohnT]

Scary! Some regulation, such as electrical inspections, keep us safe from unsafe electrical installations.

Did you need a COO (certificate of occupancy) for your house?

Is it that they don't require it or someone just forgot to tell them? Usually when you apply for the building permit they set a flag for the inspectors. Did you file a building permit?

Also, my utility company required an inspection before placing the meter to ensure the wiring beyond the meter was code.

No, there are no building permits required, no COO, no inspections of any type. Just the septic permit. Even in smaller towns, there is no code, permit or inspection at all.

 

[oilengineer]

Update: the power company brought their main electrician out and he inspected all wiring and checked voltage readings everywhere. The primary power at the road was shut off and the voltage increased at the pool 1 volt. I suggested they cut the neutral too (I had read about this on this website and other places on the internet) instead of just the hot wires. Once he did that, there was no voltage at the pool. We went out to the primary and they measured 3.5 volts in the air and 2.6 volts using a wire. They see the problem now and will ask the engineering department and operations manager how to solve the problem.