Change Summary

• In-ground swimming pool structures are not permitted to be used as a grounding electrode.

Expert Analysis

Detached buildings or structures with electrical power from a feeder — such as detached garages, workshops, etc. — require that a grounding electrode system be established and installed in accordance with the requirements of 250.32(A). Occasionally, these detached structures are located near in-ground permanently installed swimming pools. When this situation occurs, it has been documented that the electrical installer will sometimes run a grounding electrode conductor from the electrical subpanel at the detached structure to the reinforcing steel of the conductive pool shell (belly steel) or to the structural steel of the perimeter surfaces (deck steel) with the intent to identify the pool reinforcing steel as an “other local metal underground system or structure” as described at 250.52(A)(8). Unfortunately, this action is sometimes at the request of the local AHJ. This action would make the swimming pool in question (and its inhabitants) a “super-target” for any stray currents or ground-fault current introduced on this grounding electrode system, and could potentially introduce safety hazards to the occupants of the pool during events such as lightning-induced stray currents.

For the 2017 NEC, language was added at 250.52(B) to prohibit the use of the structures and structural reinforcing steel of an in-ground swimming pool as described in 680.26(B)(1) and (B)(2) from being used as a grounding electrode in the manner described above. CMP-5 determined that it was never the intent of the NEC to use a pool bonding grid as a grounding electrode. Adding the additional requirement to prohibit the use of the metal components of an in-ground swimming pool is an important clarification to point out the difference between grounding and bonding. The equipotential bonding requirements of 680.26 are to reduce voltage gradients (difference of voltage potential between two conducting objects), and not to create a grounding electrode system for a building or structure.

This point is further illustrated in the current language at 680.26(B), which states in part that “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.”