Code Change Summary: The rules on sizing a supply-side bonding jumper for parallel conductor installations have been restructured.

In the 2020 NEC^®, determining the size of a supply-side bonding jumper (SSBJ) for paralleled conductor installations required a combination of the language (in paragraph form) from Section 250.102(C)(2) as well as language from applicable notes under Table 250.102(C)(1).

In the 2023 NEC^® the two existing methods of sizing a SSBJ for parallel conductor installations have been formatted into a numerical list for ease of use and the notes under Table 250.102(C)(1) have been shortened up.

When determining the size of a SSBJ, one must first decide which method to use:

1. Install a separate SSBJ from each parallel raceway or cable containing ungrounded supply conductors. If 3 parallel sets are used (as in method 1 in the image), there will be 3 SSBJ’s, one for each raceway.
2. Daisy chain a single SSBJ between multiple raceways or cables containing the ungrounded supply conductors. If 3 parallel sets are used (as in method 2 in the image), there will be 1 SSBJ connecting all parallel raceways.

If method 1 above is selected, the SSBJ is sized from Table 250.102(C)(1) based on the largest ungrounded supply conductor in each individual raceway or cable of the parallel set containing the supply conductors.

If method 2 above is selected, the SSBJ is sized from Table 250.102(C)(1) based on the sum of largest ungrounded supply conductor (per phase) in each individual raceway or cable of the parallel set containing the supply conductors. Basically, for phase A, one would add the circular mil area of the supply conductors together and consider it as a single conductor for the application of Table 250.102(C)(1).

For methods 1 and 2 above, if the largest ungrounded supply conductor in the raceway for method 1, or equivalent circular mil area for the ungrounded parallel supply conductors per phase in method 2 exceeds 1100 kcmil copper or 1750 kcmil aluminum, the SSBJ must have an area not less than 12 ½% of the area of the largest ungrounded parallel supply conductors.

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 2023 NEC^® edition of NFPA 70.