Code Change Summary: Language was added to ensure that each individual space inside a box with a barrier is calculated separately.

In the 2017 NEC^®, Section 314.16(A) was changed to require the volume of barriers installed in boxes to be counted when performing box volume calculations. That being said, it is only fitting that another code change in 314.16(B) would require the individual space on each side of a barrier within the box to be calculated separately.

This code change needs to be applied carefully when performing box fill calculations. Here are a few things to consider:

First, where one or more internal cable clamps, whether factory or field supplied, are present in the box, a single volume allowance in accordance with Table 314.16(B) shall be made based on the largest conductor present in the box. Without a barrier in the box, a box with four internal cable clamps would only have one single volume allowance made for the all cable clamps in the box. Once a barrier is installed in the middle, there would be two cable clamps on each side of the barrier. In this case, the same box would now have two volume allowances for cable clamps; one for each space separated by a divider. The same principle would apply to equipment grounding conductors installed on each side of the barrier.

Installing a barrier in a box could potentially result in a significant change in the overall allowable conductor fill depending on what is in the box.

Below is a preview of Article 314. 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.