Results from the EPRI Swimming Pool Test Structure. Doug Dorr EPRI Melinda Norris Southern Company Marty Page Georgia Power

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1 Results from the EPRI Swimming Pool Test Structure Doug Dorr EPRI Melinda Norris Southern Company Marty Page Georgia Power

2 Equipotential Bonding for Swimming Pools and Spas Testing at the EPRI Lenox Swimming Pool Test Structure

3 Red Lines indicate location of measurement rods. They should be 32 long - spaced out from pool water at 1ft, 2ft, 3ft, 4ft, 6ft, 10ft. Put them into1/2 or 1 inch PVC so they can be accessed from the surface. PVC should extend about 1 inch above surface of concrete and terminate at dirt level. Yellow Lines indicate 12inch spacing between deck sections to be backfilled with gravel. Purple ring is #8 bare copper to be laid on surface of gravel before concrete is poured. Conductive Concrete No Rebar Concrete w/rebar Concrete w/fiberglass Gravel or Paver Option

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8 Swimming Pool Test Structure

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13 Compare to No Rebar where the voltages at 1-3 feet from pool water can range from 15 Vac to 100 s of volts Depending on the distribution voltage level

14 Comparisons of Concrete Topologies During NEV Tests

15 Comparisons of Concrete Topologies During Nearby 700 V Fault to Ground

16 Comparisons of Concrete Topologies During Nearby 2700 V Fault to Ground

17 Key Conclusions: For pools with no wire mesh in the concrete deck and owner does not want to install new deck with the wire mesh: The best mitigation option is a double (or a triple) equipotential ring configuration While the ring option is effective, wire mesh is still better = Underwater Luminaire = Metal Handrail = Ladder = Ground Rod If outer ring does not adequately mitigate perception complaints Inner rings cut into concrete provide improved performance Water Pump and Sub Panel Green Ring = NEC Art Required #8 solid copper bonding conductor Maroon Rings = Optional supplemental equipotential rings that will help mitigate perception issues Note that the optional rings must be solidly bonded to the bonding conductor

18 Key Conclusions: The NEC Code required (bonded rebar or reinforcing wire mesh) in the concrete decking material is by far the best option During the steady state neutral to earth voltage (NEV) testing, voltage potentials between the water and the surrounding deck (with the reinforcing wire mesh) never exceeded 100 millivolts AC During temporary fault conditions (with thousand-plus volt) ground energization conditions the voltage between the water and the wire mesh never exceeded 700 millivolts

19 Key Conclusion: Where Nearby Distribution Faults are Not a Concern: A single outer ring with ground rods or a single inner ring, embedded in the concrete within 30 inches of the pool water provide reasonable NEV mitigation = Underwater Luminaire = Metal Handrail = Ladder = Ground Rod If outer ring does not adequately mitigate perception complaints Inner rings cut into concrete provide improved performance Water Pump and Sub Panel Green Ring = NEC Art Required #8 solid copper bonding conductor Maroon Rings = Optional supplemental equipotential rings that will help mitigate perception issues Note that the optional rings must be solidly bonded to the bonding conductor

20 The 2010 follow-on tests will focus on three areas of high interest and intend to answer the following questions: How much additional benefit do two inner mitigation rings cut into the concrete provide as compared to just the single inner ring and what is the optimal distance from the water for best performance? What is the precise comparison during faults of the optimum retro-fit configuration versus the NEC recommended equipotential grid during distribution faults?

21 More insights into currents flowing in the earth Coating Options: Can a rugged conductive coating be applied to a pool deck to provide similar performance to the NEC recommended equipotential grid? Or can a rugged insulating coating be applied to a pool deck to provide an alternative option?