Temperature effects on Flexible Cords where Tma > 30 C

[chrisv]

Hi folks,

Long time reader, first time poster. Couldn't resist.

First, thanks for all the helpful information you've posted throughout the years! This site really is amazing trove of knowledge.

Second, I'm trying to work through an ampacity derating of flexible cord under NEC 2008 Section 400.5 where the ambient temperature (Tma) is 50 C. I see from 400.5(A) the following:

Where cords are used in ambient temperatures exceeding 30 C, the temperature correction factors from Table 310.16 that correspond to the temperature rating of the cord shall be applied to the ampacity from Table 400.5(B).

As I flip over to Table 400.5(B), I learn that the caption is "Ampacity of Cable Types SC, SCE, SCT, PPE, G, G-GC, and W" ... which would be straight forward and make a lot of sense if I were to use one of those cable types.

Instead, I'm using SEOOW cord, which is covered under Table 400.5(A). Best as I've tried, I can't find any language in the NEC code that specifically relates temperature derating and Table 400.5(A).

So I'm hoping someone here can set me straight. A few direct questions:

1. Is temperature derating on the values in Table 400.5(A) required?
2. What is the relationship (if any exists) between Table 310.16 and Tables 400.5(A/B) when sizing a flexible cable?

Thanks for your help!

Chris

 

[pete m.]

The way I take this is that table 400.5(A) is strictly for temperatures that do not exceed 30 degrees Celcius. Once you exceed this temperature 400.5(A) requires you to use the ampacity given in 400.5(B) regardless of "type" of cable. In table 400.5(B) you match the temperature rating of the cable you are employing to begin your correction for the ambient. I believe that the resulting adjusted ampacity (for the ambient) can still not exceed the allowable ampacity for the actual type of cable employed in accordance with table 400.5(A) meaning that you may have to increase the conductor size of the cable you wish to use.

Thats my 2 cents.

Pete