Twice in 2 days I have been told by 2 different people that a pool needs a ground rod. I don't see it anywhere in 680. What gives? And... It is OK to reduce the burial depth to 12" for PVC conduit on a 120 volt, 20 amp filter pump if GFCI protection is ahead of the run. Correct?
[This message has been edited by Redsy (edited 06-15-2002).]
The object of the required pool bonding it to create an equal potential between all conductive objects in and near the pool. Installing ground rods will have no effect. They are not required by the code. In some rare cases with high earth current flow (caused by an open neutral on the utility high voltage URD cable) the addition of ground rods could possibly increase the hazard. Don
Re: Swimming pool installation#81016 06/16/0202:49 PM06/16/0202:49 PM
Sparky, It would take a number of things to happen to create a problem, but it is possible. With current flow through the earth, and ground rods in the path of this current, we make the pool equipment and water part of the current carrying path for this current. If the bonding isn't perfect, we then have a difference of potential within the pool space. Without the ground rods there would be less of this earth current flowing through the bonded system. If the bonding is 100% perfect, it won't make any difference as the people in the pool would not be exposed to any potential differences. It would be like the bird on the wire, but with problems in the bonding and earth current flow and the water we could have a problem. The earth current would be flowing in the water as a result of the bonding problem. The person in the water is a better conductor than is the water itself, so the person becomes a shunt and more current will flow on the person than the water. Yes, this would be somewhat rare, but it is not unheard of. There have been some cases reported when people in pools have been shocked because of open utility underground neutrals in the area. The fact that the primary and secondary neutrals are bonded together, makes this problem worse. With primary/secondary neutral bond and an open primary neutral, we will always have current flow through the pool as a result of the bonding connection to the pool pump EGC. Additional ground rods could make this problem worse. Maybe the best installation would be to require isolation transformers, double insulated equipment, nonmetallic pool piping, and no EGC for pool systems. Pool area bonding would still be required to keep the pool and associated equipment at an equal potential. Don
Re: Swimming pool installation#81019 06/16/0207:14 PM06/16/0207:14 PM
Don, thanks for the rationale, and conjecture re; isolation.. this explains pool bonding as seen from external influence well....do you suppose a fault or leak to ground from the serving residence would seek to make way thru the motor EGC in the same manner??