Wireway Derating

[Richard S]

We are working in an existing facility that has multi section panels utilizing wireways for branch circuit distribution (see attached pictures). In these wireways, they installed DIN rail and terminal blocks for splicing. 376.56(A) allows for splices and taps in wireways (2014 NEC). 376.56(B) addresses the use of power distribution blocks, but I'm not sure if DIN rail mounted terminal blocks would be considered a power distribution block.

Of greater concerning is the percent fill and number of current carrying conductors adjustment factors. I've read numbers posts on the number of conductors in wireways and I'm still not clear on 376.22(A) and (B).
376.22(A) Cross-Sectional Areas of Wireway. The sum of the cross-sectional areas of all contained conductors at any cross section of a wireway shall not exceed 20 percent of the interior cross-sectional area of the wireway.
376.22(B) Adjustment Factors. The adjustment factors in 310.15(B)(3)(a) shall be applied only where the number of current-carrying conductors, including neutral conductors classified as current-carrying under the provisions of 310.15(B)(5), exceeds 30 at any cross section of the wireway.

The way I understand it is that a wireway can't exceed 20% fill "AT ANY CROSS SECTION OF THE WIREWAY." Ampacity adjustment per 310.15(B)(3)(a) is required when the number off current carrying conductors exceeds 30 "AT ANY CROSS SECTION OF THE WIREWAY" (I see the "AT ANY CROSS SECTION OF THE WIREWAY" is new to the 2014 code for 376.22(B)). Therefore even if I have more that 30 current carry conductors in a wireway as long as they don't traverse the wireway so that any section of the wireway has more than 30, then there is no need adjust ampacity per 310.15(B)(3)(a).

Am I interpreting this correct or do the adjustment factors come into play once the number of current carrying conductors in the entire wireway exceeds 30?

 

[infinity]

You would need to have more than 30 at any cross section of the wireway to require derating. The wording was added to the 2014 for clarity but didn't change the earlier code requirement.

 

[Richard S]

You would need to have more than 30 at any cross section of the wireway to require derating. The wording was added to the 2014 for clarity but didn't change the earlier code requirement.

Thank you sir for your reply. My next clarification would be on the cross sectional area. These are 12"x12"x60" wireways mounted horizontally. When the code references "cross sectional area" I would consider that a vertical slice in the 12x12 area. Would the code also pertain to a horizontal slice in the 12x60 area? If so the install has major issues.

 

[GoldDigger]

Thank you sir for your reply. My next clarification would be on the cross sectional area. These are 12"x12"x60" wireways mounted horizontally. When the code references "cross sectional area" I would consider that a vertical slice in the 12x12 area. Would the code also pertain to a horizontal slice in the 12x60 area? If so the install has major issues.

This has been discussed in some other threads, and the consensus was that the only reasonable interpretation is that it means "any cross section perpendicular to the longest axis of the wire way."
But an individual AHJ might still disagree.

Sent from my XT1585 using Tapatalk

 

[infinity]

This has been discussed in some other threads, and the consensus was that the only reasonable interpretation is that it means "any cross section perpendicular to the longest axis of the wire way."
But an individual AHJ might still disagree.

That would be my interpretation as well, although with a 12"X12"X12" wireway it gets tricky.

 

[iwire]

That would be my interpretation as well, although with a 12"X12"X12" wireway it gets tricky.

No direction over 24" so we are good to go.