Code Change Summary: Chapter 9, Note 9 was expanded to clarify the rules on calculating cables in a conduit or raceway.

Chapter 9, Note 9 previously stated that multiconductor cable, optical fiber cable, or flexible cord of two or more conductors is treated as a single conductor for calculating the percentage of conduit or tubing fill area. For cables that have elliptical cross sections (such as NM cable), the cross-sectional area calculation is based on using the major diameter of the ellipse as a circle diameter.

In the 2017 NEC^®, additional language was inserted to address other configurations of conductor assemblies in a conduit or raceway. Now, assemblies of single insulated conductors without an overall covering are not considered as a cable when determining conduit or tubing fill area. The conduit or tubing fill for the assemblies is calculated based upon the individual conductors.

The issue behind the code change is a newer practice of twisting individual conductors together and then placing the assembly on one reel for shipping and installation. These conductors have been mistakenly thought of as a cable when it comes to figuring the amount of raceway fill. The new code change makes it clear that they cannot be considered as a cable but are counted individually when determining raceway fill.

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 2017 NEC^® edition of NFPA 70.