Code Change Summary: Revised code language on bonding metal water piping systems.

According to NEC^® 250.52(A)(1), metal underground water piping that is electrically continuous and in direct contact with the earth for at least 10 feet qualifies as a grounding electrode.

The grounding electrode conductor between the water pipe grounding electrode mentioned above and the service is sized from NEC^® Table 250.66 which never requires larger than 3/0 copper or 250 kcmil aluminum.

Since the 2014 NEC^®, Table 250.66 has only applied to grounding electrode conductors. Prior to that, Table 250.66 was used to size other items including grounding electrode conductors, grounded conductors, main bonding jumpers, system bonding jumpers, supply-side bonding jumpers and bonding jumpers to other metal water piping that did not qualify as a grounding electrode.

The bonding jumper from the service to other metal water piping not meeting the criteria in 250.52(A)(1) is currently sized from NEC^® Table 250.102(C)(1) but in the 2014 NEC^®, was sized from Table 250.66 and never had to be larger than 3/0 copper or 250 kcmil aluminum.

In the 2017 NEC^®, a proposal was accepted to change a code reference in 250.104(A)(1) which resulted in a bonding jumper to other metal water piping having to be sized using the same method for other items in Table 250.102(C)(1) using the 12 ½% rule (from note 2 under the table) when the largest ungrounded conductor exceeded 1100 kcmil copper or 1750 kcmil aluminum.

In the 2020 NEC^®, this mistake was corrected and now, a bonding jumper to other metal water piping (that does not qualify as a grounding electrode) is never required to be larger than 3/0 copper or 250 kcmil aluminum.

Below is a preview of the NEC^®. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC^® edition of NFPA 70.