Overview

If an electrical service is grounded at any point, Subsection 250.24(D) requires the grounded conductor to be brought to each service disconnecting means. The purpose of this is to allow for the main bonding jumper to bond the grounded conductor and ground together at the main service. In previous editions of the NEC, the rules in Subsection 250.24(C)(2), which cover the grounding of service-supplied alternating-current systems where conductors are connected in parallel in two or more raceways or cables, contained grammatical errors, which made it difficult to interpret the requirements. The 2023 NEC has revised these requirements to make them clearer, and has moved them from Subsection 250.24(C)(2) to Subsection 250.24(D)(2).

Applying the 2023 Code

The 2023 NEC has moved Subsection 250.24(C)(2) to Subsection 250.24(D)(2). With this change, the language was changed to clarify previous confusion due to poor wording. Previously, the requirement stated that if the ungrounded service entrance cables are installed in parallel, the grounded conductor must also be installed in parallel. The language has changed the word “installed” to “connected” in the 2023 NEC. This more clearly states the intentions of the Code. Furthermore, the previous requirements in this subsection went on to say that the size of the grounded conductor is based on the area of the conductors “in the raceway or cable”. This was unclear if the rules are stating the total equivalent size of the conductors, or only the conductors in each individual raceway. The 2023 NEC clarifies this by adding Subsection 250.24(D)(2)(a), which clarifies that it is to be sized off of the ungrounded conductors in each individual raceway.

What’s New for the 2023 NEC?

2020 NEC

In the 2020 NEC Subsection 250.24(C)(2) read as follows (excluding exception):

250.24(C)(2) Parallel Conductors in Two or More Raceways or Cables.
If the ungrounded service-entrance conductors are installed in parallel in two or more raceways or cables, the grounded conductor shall also be installed in parallel. The size of the grounded conductor in each raceway or cable shall be based on the total circular mil area of the parallel ungrounded conductors in the raceway or cable, as indicated in 250.24(C)⁠(1) , but not smaller than 1/0 AWG.

2023 NEC

In the 2023 NEC Subsection 250.24(C)(2) was moved to 250.24(D)(2), and reads as follows (excluding informational note):

(2) Conductors Connected in Parallel in Two or More Raceways or Cables.
If the ungrounded service-entrance conductors are connected in parallel in two or more raceways or cables, the grounded conductors shall also be installed in each raceway or cable and shall be connected in parallel. The size of each grounded conductor(s) in each raceway or cable shall not be smaller than 1/0 AWG and shall be sized in accordance with 250.24(D)(2)(a) or (D)(2)(b) in accordance with 250.24(D)(1).
(a) Shall be based on the largest ungrounded conductor in each raceway or cable.
(b) Shall be based on the sum of the circular mil areas of the largest ungrounded conductors from each set connected in parallel in each raceway or cable.