Swimming pool bonding/grounding

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bubblehead

Member
Location
Richmond, VA
I am a facilities mgr with 8 facilities and 19 swimming pools. We seem to be having a problem with what, in the pool industry, is generally refered to as bonding. Bonding as I know it is as follows, please correct me if I'm wrong:


* Bonding is not grounding. Bonding should not be connected to ground inside panels.
* Connects any metal part that touches pool water to the rebar frame of the pool.
* #8 solid wire is used and it is clamped to the rebar frame, splices, and any equipment that touches pool water.
* One inspector at one of our facilities had us bond the aluminum frames of the windows in the pool area. The use of a galvanized screw and copper clamp onto an aluminum frame passed inspection. There is no requiremrnt for brazing , soldering or welding any of these connections.
* Provides an "equaipotential" grid of the pool area "to reduce earth voltage gradients". I have heard some discussion of extending this grid to no less than 5' from the outside edge of the pool beam. Pool builders and construction electricians have not heard of it.
* It is easy to see an un-bonded metal component in a pool. It will rust or corrode to pieces in short order due to electrolysis or galvanic action.

The increased popularity of chlorine generation has made bonding, if that is the term I should be using, very important for control and longevity of our swimming pools for two reasons:

1. The increased conductivity of the water with up to 5000ppm of salt added turns the pool into a very large battery. The current (DC) will corrode doner metals and deposit the dissolved metal somewhere else. This process will continue until all of the doner metals have been corroded completely. Copper and aluminum are very susceptible and go first.
I look to bonding to NEUTRALIZE this current by effectively shorting out the DC voltage between these metalic components. Somehow, the DC voltage has to be held to 0v by the bonding. I don't see any room for poor connections in the grid anywhere.

2. Pool automation works by measuring small DC voltages in the water - from 600-800mv DC for chlorine and pH measurments. The bonding should keep the stray DC voltage to zero, if it works like I think it does, but we also need to eliminate the AC component that may be present from ground current, either direct or induced. We are begining to see pools at about five years old that begin to pick up stray voltage in the water and causes the sensor probes to not track. I'm thinking corroded bonding connections under the pool

We have taken some steps to deal with the problem - installing harmonic rejection transformers for pool equipment room panels and eliminating pool-water reheat form the rooftop dehumidification units (eliminates copper pipe connection from hi voltage to low voltge pool equipment) but results are not in yet because these are newer facilities. We also cleaned the bonding connections on all of the equipment at an older facility and saw a reduction on the wandering of the sensors but it was not eliminated.

Can we talk about this?

Thanks
 

wbalsam1

Senior Member
Location
Upper Jay, NY
I suggest that you familiarize yourself with the definitions within Article 100 and Article 680 of the NEC and as Stickboy has mentioned, read Article 680. Study equipotential planes, too. Welcome to the forum. :smile:
Also, a google search for stray voltage might be helpful, too. It's all learning and this forum is a great tool.
 

bubblehead

Member
Location
Richmond, VA
We have numerous variable speed motors in the facility which can cause a lot of harmonics in the power distribution for the buildings. This in turn causes problems in neutrals, transformers and motors overheating, and can cause problems with generation of DC voltages in electronic equipment (computer) power supplies. Pool automation controllers are computers with sensors that measure millvolts and chlorine generators are similar electronically controlled devices. A pool equipment room probably has at least 100 inductive devices (motors, buck/bosters, coils, transformers, etc.) and 10 or more electronic power supplies that could be affected by harmonics. The most costly would be overheating of motors and transformers causing short life, and disruption of control equipment by loss of DC power supply control. By design, all of the equipment that touches pool water is fed by one harmonic rejection transformer through the panels in the equipment room unless it is a hivoltage component, such as a large pump or roof top dehumidifier.
 

bphgravity

Senior Member
Location
Florida
I would guess your problem is not coming from stray voltage, but could technically be classified as objectionable current. Here's why.

In your first statement, you write, "Bonding should not be connected to ground inside panels." While this would be effective in removing this objectionable current, it is nearly impossible to acheive as many of the items that must be bonded to the equipotential grid are also connected to an equipment grounding conductor that connects all the way back to the service grounded conductor at some point.

As we all know, normally operating current will flow back to the source through all available paths. A pool makes an excellent grounding electrode. The bonding grid and its connection to the equipment grounding system places normally operating current on the pool and its equipment.

All the bonding in the world will not eliminate this current.
 

bubblehead

Member
Location
Richmond, VA
Yes, I didnt think about the grounding in the motors , heaters, etc, all of which are bonded. This problem of sensors not tracking has only recently occured after 5 years of smooth operation. We assumed it was the automation equipment and changed out the controller and sensors (all of the automation components) but the problem remains.
Some other conditions exist which we think are unusual: The 2" copper piping that goes to the roof top dehumidifier has been perforated from the inside out with multiple pin holes. It seemed like we were getting a new leak every day. We replaced the copper with PVC but are worried about the heat exchanger in the rtu because the pool water is still connecting it to everything else. When we cut the copper pipe open it was coverd with small pits about the size of a pencil lead. Also, brass valves are doing the same thing.
Would it be possible that there is some potential between the hi voltage rtu and the lo voltage pool equipment that could cause this problem through the pool water?
Whatever the source, there is some voltage or current in the water that is disrupting the sensors and causing them not to track at all.
Can you tell me what type of person I should contact to get started on solving this problem?

Thanks for your help.
 
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