Code Change Summary: New requirements were added for power distribution blocks ahead of a service disconnect.

Power distribution blocks are often used for splicing service-entrance conductors in metal wireways (covered in Article 376).

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 were 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 service equipment with no regard to the suitability of the product being located on the line or load side of an overcurrent protection device.

Since the above code language was only found in Article 376, it was only 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) with the intent to have the rules apply to power distribution blocks in any box or enclosure.

In the 2020 NEC^®, the language previously located in 314.28(E)(1) was revised and relocated to 230.46 and now applies to power distribution blocks used with service-entrance conductors regardless of the enclosure type they are used in.

The revised 2020 requirements specify the following:

• Power distribution blocks, pressure connectors, and devices for splicing or tapping service-entrance conductors shall be listed
• Power distribution blocks installed on service conductors shall be marked “suitable for use on the line side of the service equipment” or equivalent
• Effective January 1, 2023, not just power distribution blocks, but any pressure connector or device used to splice or tap service conductors shall be marked “suitable for use on the line side of the service equipment” or equivalent.

The post date of 2023 provides time for product safety standards to catch up and test methods to be established that will address free-floating wire splices or devices that are not necessarily meant to be connected to the enclosure but generally connect other conductors of the same polarity. These devices move with the spliced conductors during a high-level fault condition and have not been required thus far to be tested in the same way that a power distribution block that is bolted to the enclosure is.

Power distribution blocks (suitable on the line side of service equipment) must be able to withstand opposing forces that can occur during a fault condition when the service conductor is likely to whip or move. Power distribution blocks often hold conductors of different phase, polarity or ground.

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 2020 NEC^® edition of NFPA 70.