2017 NEC 336.10(3) vs 336.10(9)

[BarklieEstes]

I am having a discussion with an inspection supervisor about the allowable ampacity of #8 TC-ER cable in a raceway for a one-family dwelling.

The inspector's understanding is that i) if it's in a one-family dwelling, ii) if it contains power and control conductors, and iii) if is identified for pulling through structural members then I must follow the stipulation to use the Part II of Article 334 and thus use the 60° Column. I object on two points:

The first is my understanding of the structure of the NEC, which is that permissions, by their nature, never disallow things [90.5(B)]. 336.10(3) allows me to put the cable in a raceway, and 336.80 tells me the ampacity must be in accordance with 310.15 (75° Column). The existence of 336.10(9) is irrelevant if I am not using it.

The second is specific, which is that 336.10(9) is for exposed runs, as clarified in 336.12(2). If I am using it in a raceway, then it is obviously not an exposed run.

Regards,
Barklie Estes

 

[wwhitney]

I agree in principle, but it is clear that the NEC writers are using the 3xx.10 sections differently. For example, 330.10(A)(1) for MC cable just says "For services, feeders, and branch circuits." If we get to stop reading there in 330.10(A), that means it's a blanket allowance for any premises wiring, and we could just delete the rest of the section. So we do have to read the whole section.

On the specific case in hand, the question is whether the second sentence in 336.10(9) that says "Type TC-ER cable used as interior wiring shall be installed per the requirements of Part II of Article 334" is implicitly limited to the case that you are utilizing the permission granted in the first sentence. I would say yes. If you take the second sentence out of context and apply it to other installations, then it requires compliance with Part II of Article 334 for all interior wiring, which pretty clearly is not the intention.

You could pose the following question to the inspector: say the cable in question did not have the -ER rating. Then it couldn't be installed under 336.10(9). The installation would still be allowed under 336.10(3), and as 336.10(9) is not in play, there's no question of the cable being limited to the 60C rating under the reference to Article 334 in 336.10(9). So does the inspector really want to say that the cable's extra unnecessary additional rating is going to decrease the ampacity, rather than just provide additional options for the installer?

Cheers, Wayne