Code Change Summary: New requirements were added about the listing of power distribution blocks.

Power distribution blocks are most commonly used in metal wireways (covered in Article 376) but there is nothing prohibiting their use in other enclosures.

In the 2014 NEC^®, code language was added in 376.56(B)(1) to ensure that power distribution blocks installed on the line side of the service equipment are listed for the purpose. Before the code language was added, it was common practice to see any kind of power distribution block used ahead of a service disconnect with no regard to the suitability of the product being located on the line side of any overcurrent protection.

By locating the above code language only in Article 376, it would only be applicable if the power distribution blocks were installed in a metal wireway.

In the 2017 NEC^®, similar code language was added to 314.28(E)(1). Now that the requirement is also repeated in Article 314, it will apply to power distribution blocks in any box or enclosure.

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.