Re: Pool Bonding
The supplemental electrode is required to connect within the 5 foot area of the piping. Not connect back to the neutral bus.
In 250.53 (D) (2) It give us the places that we can connect the Supplemental Electrode to.
Supplemental Electrode Required. A metal underground water pipe shall be supplemented by an additional electrode of a type specified in 250.52(A)(2) through (A)(7). Where the supplemental electrode is a rod, pipe, or plate type, it shall comply with 250.56.
The supplemental electrode shall be permitted to be bonded to the grounding electrode conductor, the grounded service-entrance conductor, the nonflexible grounded service raceway, or any grounded service enclosure .
Now with that out of the way.
I cant understand why there would be common mode voltage on the pool if the EGC from the pump circuit is connected to the pool bonding wire.
First there has to be a load (current) across a resistance (wire) To have a voltage on the pool bond the only wire that would affect this pool bond would be the neutral from the service to the transformer the voltage drop in this wire would appear on the grounding grid of the whole house as there is no current (at least shouldn't be) on the pool bonding or grounds after the main panel.
yes there will be what we call stray voltage on the grounds that come from the water line because of the parallel connection to another service down the road. but in a normal installation this would be kept to a minimum, yes there could be faults with the power lines I.E. loss of the primary neutral loss of the secondary neutral at ether this service or one down the road but these are not normal and the NEC don't address this. If there is one connection that I could change it would be the bond from the primary neutral to the secondary neutral this connection causes most of the stray voltage problem that we see if it were not there, there would be no common connection to cause the primary to try to draw current from the GE's on the secondary side of the circuits.
The other is the connection of the house water pipe to the main water line at the street. there would be a isolator coupling to prevent the parallel connection of two or more services on the same transformer.
but for the most part the voltages induced into the grounding system of a service is not high enough to cause a problem and in the cases of where an underground service lateral conductors Failed that caused shocks in a pool it was the fact that there probably was no kind of bonding at the bottom of the pool that would of prevented the voltage gradient from the ladder to the pool bottom. the other is these service lateral conductors ran under this pool if I remember right which should not ever been done.
Feature two ground electrodes 100 feet apart. One is the water line, the other is a driven rod.
The water line will have low impedance compared to the rod. More current will flow in the conductor to the water line.
This is true but why would there be any current on these EGC's?
Again this would not be somthing that would be there in a normal installation.
and the lower impedance rod would hold the voltage at a lower level to the earth potential.
The shocks that happen in and around pools are caused by bad instalations and loads on the grounding and grounding connected to the neutral buss after the main service and faulty appliances.
not code compliant installations.
the other side of the equasion is the POCO's could give us some better safegards to prevent the stray current from getting from the primary side of the transformer to the secondary side and the water co's could prevent the parralleling of the neutrals between two services by installing a isolating connection at the streat main.
Stray voltage can only be eliminated when there is a lower impedance path for the current back to the source of the stray voltage thus shorting it out. or a path around the area neening the protection.
