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).]

Redsy,

I have not heard of a Ground Rod being required. Maybe it is a local requirement?

Table 300.5 Column 4 says that 12 inches of cover is adequate for Residential applications under these conditions.

Bill

would'nt a rod or two establish a better gradient?

Sparky,

I was wondering the same thing myself, especially in situations where there are no metal components to bond to. I have not heard of it being required anywhere though.

Bill

Redsy, we are required to drive a rod by our inspector. It connects the pool grid, rod and motors with one solid egc. Never questioned it but never seen the NEC require it either.

Bill, from my experience I have never seen a pool (in-ground) that didn't have something to bond. Lights and ladders of course but the concrete rebar and mesh require it too.

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

Don,
that's an interesting twist from our 'more is better' grounding mentality, can you expand a tad?

I have never seen a second ground rod needed for a pool. Why the rebar that is grounded in the pool should be a great grounding electrode, right? ( If it is an inground pool with rebar.)
Harold

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

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??

arseegee,

I don't know how common it is anymore, but I have seen pools made from Concrete Block and even wooden Frames. (which have had to be replaced) Recently I've seen Plastic being used too. They don't seem to use Concrete w/rebar much where I am except for Commercial pools.

Bill

Sparky,
Yes, the code requirements for bonding and grounding make the pool a current carrying conductor. The current is limited by the impedance of the parallel paths and the most current will be on the grounded conductor as long as it is intact. The neutral current would also flow on the following, listed in order from most to least current. Metal underground water pipe system, TV cable shield, ufer ground, pool bonding and lastly on the driven ground rod.
Don