Ampacity

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J.roth0864@brightwood.edu

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What is the ampacity for each of eight No. 2 THWN copper current carrying conductors installed in a single conduit.
A.) 57.5A
B.) 80.5A
C.) 91A
D.) 92A

I have been looking in the NEC for this answer for the last 30 minutes and I will think that I have found it but then the answers that I come to on the charts don't match any of the possible answers I have listed. In what section would I find the answer to this and once it is found how would I do the calculations would be needed to come to the correct answer ?
 
J.roth0864@brightwood.edu said:
What is the ampacity for each of eight No. 2 THWN copper current carrying conductors installed in a single conduit.
A.) 57.5A
B.) 80.5A
C.) 91A
D.) 92A

I have been looking in the NEC for this answer for the last 30 minutes and I will think that I have found it but then the answers that I come to on the charts don't match any of the possible answers I have listed. In what section would I find the answer to this and once it is found how would I do the calculations would be needed to come to the correct answer ?
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The tables show the ampacity for up to three conductors in a single raceway.

You have eight conductors so the table ampacity has to be adjusted down.

Have you been taught how to derate?
 
As a further step in you education, after you look at 310.15(B)(3)(a) take a peek at 110.14(C). It does not change you answer on ampacity but it' an often overlooked section when selecting conductors.
 
augie47 said:
As a further step in you education, after you look at 310.15(B)(3)(a) take a peek at 110.14(C). It does not change you answer on ampacity but it' an often overlooked section when selecting conductors.
Click to expand...
What that amounts to is 110.14(C) is part of the minimum conductor size determination. It is based on ampacity determined a certain way...

Then there is a minimum conductor ampacity determination, and that's done a different way than above.

What the orignal poster (OP... and welcome btw) is asking about falls in the latter.
 
Before you use 310.15(B)(3)(a) take a look at Table 310.104. You must derate from the column of 310.15(B)(16) that corresponds to the maximum operating temperature of your conductor. For your question the correct answer is there as well as one plausible distractor.
 
RB1 said:
Before you use 310.15(B)(3)(a) take a look at Table 310.104. You must derate from the column of 310.15(B)(16) that corresponds to the maximum operating temperature of your conductor. For your question the correct answer is there as well as one plausible distractor.
Click to expand...

I love the way we are all just itching to blurt out our answers but wont.....


JAP>
 
I thought you could use the 90d column at 130 amps for derating calculations ?

Jap.
 
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