250.52(B)(3) Not Permitted for Use as Grounding Electrodes.
Code Change Summary: A new item has been added to the list of materials that are not permitted to be used as a grounding electrode.
Section 250.52(B) describes all of the items and materials that cannot be used as a grounding electrode. In the 2014 NEC®, there were only two items; metal underground gas piping systems and aluminum.
In the 2017 NEC®, item 3 was added to make it clear that the steel rebar of a pool cannot be used as an actual grounding electrode.
Even though NEC® section 680.26(B) requires the pool steel to be bonded to all other conductive components mentioned in 680.26(B)(1) through (7), it is still not permitted to be used as an actual grounding electrode.
The bonding in 680.26 is there to place everything in the pool area on the same potential which helps to eliminate voltage gradients in the area or stray voltages that can be dangerous for swimmers.
A grounding electrode system serves a different purpose altogether. One of which is to limit the voltage imposed by lightning. Using the pool steel as the grounding electrode could jeopardize swimmers who really shouldn’t be swimming during a lightning storm anyways.
Below is a preview of Article 250. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC® edition of NFPA 70.
2014 Code Language:
250.52(B) Not Permitted for Use as Grounding Electrodes. The following systems and materials shall not be used as grounding electrodes:
(1) Metal underground gas piping systems
(2) Aluminum
2017 Code Language:
250.52(B) Not Permitted for Use as Grounding Electrodes. The following systems and materials shall not be used as grounding electrodes:
(1) Metal underground gas piping systems
(2) Aluminum
(3) The structures and structural reinforcing steel described in 680.26(B)(1) and (B)(2)