The superiority of multigrounded primary distribution has been proven over time. The multiple grounds reinforce each other to provide superior resistance to lightning. Multiple grounding of the neutral also permits the earth to serve as a backup neutral so that an open neutral will not toast transformers and houses and so forth.

The amount of current that flows into an equipotential plane is limited by soil resistance. Sure, the plane cannot have zero voltage difference between one end and the other, but the idea is to lower the voltage difference to harmless levels. An euipotential grounding grid is better than no defense and has beed shown in actual case studies to be very effective.

Ungrounded secondary systems such as 480 volts ungrounded have more than their fair share of damage from silent and invisible lightning such as Saint Elmo's Fire. Some people have actually bragged to me on job interviews about how many motors they replace each.

I have been shocked twice by picking up a 1.5 volt D cell by the ends. This was because I failed to wash my hands over several hours and allowed perspiration salts to build up. I can see why cows do not like the Cow Voltmeter Method.

I have also seen and felt first hand what happens when a failed 120 volt underground electrical line is leaking 7 amps into the soil DURING A DROUGHT! The stray voltage in this situation ( about 30 to 90 volts ) far exceeds what a multigrounded neutral system normally produces. This current flow partially energizes concrete basement floor and metal drain plumbing causing correctly grounded washing machines and faucets to have a nasty tingle voltage. Since bare feet are relatively insensitive to electric shock people think that the object that they are touching is what is hot, but it is their feet that are hot.

An equipotential grounding grid around and underneath a swimming pool is for the purpose of defending the pool against EXTERNAL threats such as failed underground wiring, downed power lines, and lightning current. Against a 13,200Y23,000 volt ground fault a city block away sure would push the limit of the #8 solid wire that National Electrical Code requires but nevertheless such a ground fault typically can find better grounding electrodes elsewhere to carry most of the current.

A consistent lie in NEC is that a nonmetallic in ground swimming pool does not need an equipotential grounding grid but that can be shown to be false. All insulators, including a theoretically perfect insulator, store charge, what is known as capacitance and therefore has capacitive reactance. Capacitive reactance is the ability to resist but not stop the flow of alternating current. One of my experiences with variable frequency drives is that water increases the capacitance of allegedly waterproof insulation ( THWN ) to the point that the 2,000 Hertz or so carrier shorts out even though the circuit is only about 40 feet long.

I have sworn off swimming pools because the 3 swimming pool contractors I have encountered do not understand why an equipotential grounding grid is needed. The 3 instances are:

1. The pool that I wired in 1988 in inherently unsafe because only the pool deck and metal walls down to about 4 feet are bonded and grounded. The concrete walls below the steel wall as well as the concrete floor have NO reinforcing steel. The pool has a plastic liner but as I pointed out above the liner is a home made capacitor.

Just a few weeks ago I saw a truck for this pool contractor so they are still in business.

2. The next instance was the Mikvah bath over at Revere Road Synagogue in Akron, Ohio which was built around 1999. After I pointed out to Rabbi Sasonkin what was wrong with the installation he made the concrete contractor grind out the concrete and expose a rebar so that the electrician ( someone else ) could bond the rebars to the pump and deck.

As a side note, the Summit County electrical alleged inspectors allow aluminum service entrance cable to supply a subpanel that supplies a pool in a new installation. NEC requires such a new feeder to be in conduit.

3. The Akron General Medical Center neuroscience building has a partially in ground hydrotherapy tub that has nonmetallic walls. There was no equipotential grounding grid around and underneath the walls to intercept an Ohio Edison ground fault from forcing current through the capacitive reactance of the pool wall. Asking how much current would be like asking how much a yellow jacket sting hurts. Ohio Edison has both 2,400Y4,160 volts and 13,200Y23,000 volts running underground in this area plus extensive 120/240 volt 120Y208 volt and 240 volt corner grounded underground lines in this area.

Neither the registered professional engineer not the city plans examiner not the electrical inspector could recognize what an ad hoc capacitor looks like.

To make things worse, the nonmetallic pool manufacturers talked NFPA into repealing the 2005 NEC requirement for an equipotential grounding around the contour of any in ground swimming pool. Nonmetallic in ground pools are again exempt by civil law from needing an equipotential grounding grid but not by the laws of physics and circuit theory.

My only defense against liability then is to swear off in ground swimming pools. None of these so called experts recognizes why an equipotential grounding grid is needed.

Mike Cole mc5w at earthlink dot net Telephone: 216-524-2185 450 Meadowlane Road Seven Hills, Ohio 44131