Out By The Pool: Equipotential Bonding for Pool Perimeters and Parts

In the past few months, I have received emails and phone calls from electrical inspectors and contractors stating there is confusion in their areas concerning swimming pool equipotential bonding. They requested that I clarify the bonding requirements for swimming pools. As far back as the 1999 National Electrical Code (NEC) and for each NEC cycle through 2011, quite a few changes have dealt with bonding associated with swimming pools. I don’t recap the changes in each cycle here, but I use the text of the 2014 and 2017 Codes to explain the bonding requirements in Section 680.26, since these two cycles have seen only minor changes to the text.

The purpose of bonding in the area surrounding a pool, including any conductive parts within the pool or in close proximity of the pool, is stated in the performance requirement of Section 680.26(A): “The equipotential bonding required by this section shall be installed to reduce voltage gradients in the pool area.”

That simple statement then requires more than an entire page to describe the bonding requirements.

There are seven subparts to Section 680.26(B). Each subpart describes the conductive parts in or around the pool to be bonded together using solid copper conductors that are insulated, covered or bare and not smaller than 8 AWG. Rigid metal conduit, brass or other identified corrosion-resistant metal raceways can also be used to establish bonding from one metal part to another.

An 8 AWG or larger solid copper bonding conductor, provided to reduce voltage gradients in the pool area, shall not be required to be extended or attached to remote panelboards, service equipment or electrodes, since the purpose of the bonding conductor is to establish a zero-reference equipotential bond of all metal parts.

Conductive pool shells with steel rebar embedded in the concrete can be used as a bonding point for all metal parts in the pool or metal located in close proximity to the pool. Poured concrete, pneumatically applied or sprayed (gunite) concrete, or concrete blocks with painted or plastered coatings are considered conductive materials due to permeability and the porosity. Vinyl pool liners and fiberglass composite shells are considered nonconductive and cannot be used for bonding. 

Unencapsulated reinforcing steel, used in the concrete and tied together with steel tie-wire, can be used as a point of bonding connection. Encapsulated reinforcing steel with a nonconductive coating within the pool shell would require a copper conductor grid based on 680.26(B)(1)(b). This copper grid must be constructed of minimum 8 AWG bare solid copper conductors bonded to each other at all points of crossing using approved bonding connectors. 

The grid must conform to the contour of the in-ground pool and be arranged in a 12-inch-by-12-inch network of conductors in a uniformly spaced, perpendicular grid pattern with a tolerance of 4 inches (plus or minus 4 inches for the grid spacing). The grid must be secured within or under the pool at not more than 6 inches from the outer contour of the pool shell.

The perimeter around the outside of the pool must extend at least 3 feet horizontally beyond the inside walls of the pool and includes unpaved surfaces, poured concrete surfaces or any type of paving. Any dirt (unpaved surfaces), concrete or other conductive material in this established perimeter may have a difference of potential with the pool and must be bonded to the pool shell’s structural reinforcing steel. This perimeter surface bonding to the conductive reinforcing steel or the pool’s copper bonding grid must be connected by a minimum 8 AWG solid copper conductor at a minimum of four points uniformly spaced around the pool perimeter.

For nonconductive pool shells, bonding at four points is not required. The purpose of the bonding at four points uniformly around the pool is to provide an equal potential at all four points of the pool decking material.

If conductive structural reinforcing steel of the pool shell (fiberglass pools or similar nonconductive pools) is not available for bonding the horizontal perimeter surfaces, at least one minimum 8 AWG bare solid copper conductor shall be installed following the contour of the perimeter surface, splices must be listed, and the 8 AWG conductor must be installed at least 18–24 inches from the pool’s inside walls. This 8 AWG conductor must either be installed in the concrete or pavers, or, where installed under the perimeter surface, it must be 4–6 inches below the subgrade.

The text in the 2014 NEC and 2017 NEC is fairly clear, but if you are having trouble understanding it, clarification for the 2020 NEC may be necessary.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com.

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