[donf]

Okay, I'm working with a 2008 NEC study guide and I want to make sure I understand the high temperature correction process with respect to Ambient Temperatures.

I 'm given a 200 amp sunlight exposed, service drop. The area of the installation calls for an average 113(F) daily summer temp.

Using Table 310.15 (B) (6) - 200 Amp a 2/0 AWG USE cable.

To conductor sizing requirement, you divide 200 by 0.82 (for USE cable) <table 310-16
75 (C) column>. The factor is based on 45 (C) 0.82 from the table below table 310.16

So - amps 200 /0.82 = 243.9 or 244 amps. According to table 310.15 (B) (6) I would need to use a 250 kcmil cable rated for 255 Amps to meet the requirements for this installation.

255 amps X 0.82 correction factor = 209.1 amps or 209 amps.


Did I even come close to getting the process correct?

[Tev]

If you were required to apply those correction factors to the ampacities in table 310.15(B)(6) then your methodology would be sound. However, the correction factors apply only to the table they are a part of.

[donf]

Okay,

Since table 310.15 (B) (6) does not have any correction factors, then I must use 310.16 and the correction factors below that table, correct?

I cannot take advantage of the Residential Feeder ampacities in table 310.15 (B) (6), correct?

If the above is true, then the book is incorrect in its solution example.

[Tev]

I hesitate to say the book is wrong but the NEC to my knowledge does not limit the use of table 310.15(B)(6) due to temperature.

On the other hand, there is a code about not exceeding the temperature rating of conductors (310.10).

With that kind of temperature it may be a good idea to use 310.16 and use the correction factors but the correction factors attached to 310.16 do not apply to 310.15(B)(6).

I'm curious which of the 5 million study guides this is. It's possible the author lives in an area where it is common practice or even a local code to apply those factors to 310.15(B)(6). It's also possible I'm wrong. I live in an area where it just never gets hot enough to think about things like that. But now I've looked and if it's in the NEC then I can't find it. So, hesitation finished, the author at the very least is wrong to mix local practices into a study guide for the NEC. :)

[tkrussell]

To clear this up, I think we need to see the exact wording of the study guide question or problem.

Yo have USE as an exposed service drop is odd, since USE is rated for underground.


The temperature correction factors below table 310.16 are multipliers, do not divide.