Bonding of Pool Water

By Mark C. Ode | Sep 15, 2007
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There are times when an idea seems to take on a life of its own, and bonding of swimming pool water seems to be one of those. This idea was proposed for the 2005 National Electrical Code (NEC), passed at the proposal stage and was soundly rejected at the comment stage. For the 2008 NEC, it was rejected at the proposal stage. Code-Making Panel 17 stated, “The submitter has not provided adequate substantiation. There are issues with conductivity of water, changes with water temperature, current flow, size of conductors, etc., that need to be addressed.” The submitter returned at the comment stage with substantiation, and the panel accepted the proposed text for the 2008 NEC, so “bonding of pool water” will become part of the 2008 Article 680.

The text proposed for the 2005 NEC was much more extensive than the text proposed and accepted for the 2008 NEC. For the 2005 NEC, the text read, “680.26(B)(6). Pool Water. The pool water shall be effectively bonded. Pool shells made of reinforced concrete in which the water is in direct contact with the concrete and the reinforcing steel is utilized as the common bonding grid shall be considered to effectively bond the water. If non-conducting or non-reinforced material is used to form the pool shell or liner, bonding shall be accomplished via the use of metallic parts, plumbing, lighting brackets and shells, ladders, electrodes, etc. in continuous contact with the water. The metal shall be copper, brass, bronze, or other corrosion- resistant material or may be chrome plated. Metallic parts used for bonding shall have a minimum surface area in contact with the water of 200 square centimeters. Semi-conducting material may be used if the resistivity of such material is less than 0.1 ohm-centimeters. Semi-conducting material shall have a minimum of 0.5 square meters in contact with the pool water at each location and encapsulate copper conductor evenly distributed throughout. The encapsulated copper conductor shall have a total electrical area of at least 16,500 circular mils and have terminations of at least 8 AWG. Point of bonding with the pool water shall be made at no more than 4 meters distance around the circumference of the pool.”

The accepted text for the 2008 NEC reads, “680.26(C). Pool Water. An intentional bond of a minimum conductive surface area of 5806 mm2 (9 in2) shall be installed in contact with the pool water. This bond shall be permitted to consist of parts that are required to be bonded in 680.26(B).”

The accompanying text reads, “Extensive testing clearly substantiates that the potential for voltage gradient is present in pools where the pool water is not bonded via metal parts in the pool. With this knowledge and confirmation of a voltage gradient hazard, the CMP must address the issue. Test results, handed out at the Proposal Meeting, show that the presence of a touch potential exists in all areas of the pool and that the proposed solution for bonding pool water will essentially reduce that potential to zero. While the proposed solution may not be the only solution, it meets the NEC criteria of providing minimum protection for the public. The test report in its entirety has been submitted to this Comment for further review by the Panel Members. Typically, pool water is considered electrically conductive due to dissolved chemicals. Although the conductivity will vary with the temperature, the change in conductivity for all practical purposes is not a factor in the application of a proposed solution. Again, the proposed solution meets the NEC criteria of providing minimum protection for the public and should be viewed as a protection measure compared to having no protection.

“In the proposed solution, the size of bonding conductor is not specified. This is in line with several Bonded Parts described in 680.26(B). In 680.26(B)(1), (B)(2), (B)(3), and (B)(5), use of a minimum of #8 AWG size wire is implied as specified in 680.26(B)(4) and 680.26(C). In the stray voltage field, ground currents are rarely determined due to measurement difficulties and inaccuracies. On the other hand, resulting voltage gradients (stray voltages), however, are very easy to measure and can be directly used to analyze stray voltage problems and their mitigation. As evidenced by the test report, the proposed solution is based on such stray voltage measurements around a swimming pool."

There was extensive background and support information provided in the submitter’s substantiation for the comment that Panel 17 accepted.

The issues on equipotential bonding grids and pool water bonding are interesting and challenging for the pool industry, and it looks like controversy will continue for the 2008 NECEC

ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at [email protected].

About The Author

ODE is a retired lead engineering instructor at Underwriters Laboratories and is owner of Southwest Electrical Training and Consulting. Contact him at 919.949.2576 and [email protected]

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