Ambient temperature adjustment.

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Hello, I have 2 separate mc cables, one is #14 awg, and the other one #12 awg. Both are THHN/THWN, copper conductors,rated for 90C degrees. They will go in the attic where the temperature can get up to 150F degrees in the summer. What is the allowable ampacity for each cable after adjusting for this ambient temperature?
Thanks for your help.
 

iwire

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We really try not to hand out answers to those that are learning without them putting some effort into it.

What code sections do you think apply here?
 

charlie b

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This sounds like a homework assignment. We will be glad to assist. But you have to give it a try first. Let us know what you think, or where you have looked in order to try to find the answer. Then we will give you our opinions. That is how this forum works.
 
ambient temperature adjustment.

ambient temperature adjustment.

Fair enough.
310.15(3) Temperature limitations of conductors.(1)ambient temperature. (2)Heat generated internally in the conductor...
Table 310.15 (B)(2)(a) Ambient temperature correction factors based on 30C degrees (86F). Table 310.15(B)(2)(b) based on 40C degrees(104F)
(3)adjustment factors.

Thanks again.
 

don_resqcapt19

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Fair enough.
310.15(3) Temperature limitations of conductors.(1)ambient temperature. (2)Heat generated internally in the conductor...
Table 310.15 (B)(2)(a) Ambient temperature correction factors based on 30C degrees (86F). Table 310.15(B)(2)(b) based on 40C degrees(104F)
(3)adjustment factors.

Thanks again.
That is a good start. Apply the tables and do the math.
 
Hello, I have 2 separate mc cables, one is #14 awg, and the other one #12 awg. Both are THHN/THWN, copper conductors,rated for 90C degrees. They will go in the attic where the temperature can get up to 140F degrees in the summer. What is the allowable ampacity for each cable after adjusting for this ambient temperature?
Thanks for your help.

Is this correct? based on table 310.15(B)(2)(a) factors based on 30C degrees (86F)

#14 awg= 17.75 amps.

#12 awg=19.5 amps.
 
This sounds like a homework assignment. We will be glad to assist. But you have to give it a try first. Let us know what you think, or where you have looked in order to try to find the answer. Then we will give you our opinions. That is how this forum works.
It is not for homework. I took an NEC class,but this topic was not covered.

Is this answer correct? for 141-149F?
#14 awg. 25 x.65=16.25 amps.
#12awg. 30x .35=19.5 amps.

Thanks.
 

don_resqcapt19

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Location
Illinois
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retired electrician
It is not for homework. I took an NEC class,but this topic was not covered.

Is this answer correct? for 141-149F?
#14 awg. 25 x.65=16.25 amps.
#12awg. 30x .35=19.5 amps.

Thanks.
Yes, except for the typo for the #12 correction factor.
 
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