would continue until the NEC made meaningful modifications to Article 680.26.
Equipotential Grid Results:
The next set of tests are founded in research from electric power substation step-and-touch potentials and corresponding research at dairy farms with equipotential planes and gradient ramps. The simple concept is that if you want the surface above an energized system to have equal voltage across all the walking or standing surfaces of interest, you must use a conductive mesh of gridded squares or rectangles beneath the full area of interest. Three important takeaways for the Gridded Mesh tests were:
• Using the gridded squares instead of rectangles provided the best equipotential performance and required the least amount of total feet of wire for fabrication of the grid.
• Getting the grid as close to the pool deck surface as possible provided the best equipotential performance, and burying the conductive wires four to six inches beneath the subgrade was inadvisable.
• Using smaller squares makes it more difficult for a person to get their arms and feet into spots where they aren’t partially on top of the wire and extending the grid, out further from the water is a useful way to eliminate concerns where a person (holding an aluminum pole on a skimmer) could get shocked if they were standing on the deck beyond the equipotential zone.
• The improvement measured for the grid as compared to the single bare wire was dramatic, where a faulted underwater light yielded equivalent chest current measurements of 80 to 100 milliamps for the single wire and only three to five milliamps for the gridded mesh. This is the difference between an electrocution and a nuisance perceptible shock incident!
These results are consistent and repeatable, and EPRI opens the testing to any electrical inspectors or NEC Code Panel members during their annual summer training seminars. In fact, five of the subject matter experts that worked on the revised criteria found in NEC TIA 23-9 have attended and conducted their own measurements during the pool testing.
Key Takeaways
The good news for pool owners and users is that TIA 23-9 finally provides a way to avoid unnecessary fatalities and injuries to our children and to our loved ones, even when things go wrong, electrically speaking. Many such incidents have been documented in the Coast Guard report, and as time goes on, we can expect a dramatic reduction in the number of fatalities and injuries once TIA 23-9 is mandatory across the U.S.
The bad news is that even though the NFPA Standards Council ordered the inclusion of TIA 23-9 in the 2023 NEC (under an Emergency Nature provision) there remain many legacy pools that aren’t compliant with this minimum safety requirement. Those responsible for installation and for enforcement of the NEC criteria should note that these new requirements provide a minimum level of safety, and any attempt to lessen that safety by not following TIA 23-9 requirements could be considered grossly negligent.
The beauty and the simplicity of TIA 23-9 is that we no longer must worry about the type of pool construction, or about GFCI malfunctions, or questionable grounding, or even the different ways electrocutions and shock injuries can happen. TIA 23-9 provides a way to ensure that every properly bonded component and surface (including the water and the deck) will float up and down together with whatever voltage happens to be present poolside.
About the Author: Doug Dorr received his Bachelor's degree in electrical engineering from Indiana Institute of Technology, Ft. Wayne, IN, USA in 1989. He is with the Electric Power Research Institute (EPRI), Knoxville, TN, USA, where he currently leads the EPRI Distribution Modernization (data analytics) Demonstration Initiative. He has been involved with electric-power-system- related technology research for more than 30 years (including the EPRI family of companies). He is a coauthor of three electric power industry text books and numerous technical publications. His primary background is in the areas of power distribution and power quality, and standards development.
