conduit fill/derating

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dj94

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hi guys i need a bit of clairifaction.
i have an engineer telling me i need to use the termination temp. rating of my breakers (75 degrees) to calculate my conduit fill. why??? arent these 2 totally seperate issues?
7-9#12 thhn in 310.15(b)(2)a calcs at 70%
#12 thhn the 90 degree column 30amps(for calc)= 21a
if i go to the 75 degree column it = 17.5a
 
Welcome to the forum.:)

You can use the 90 degree column of Table 310.16 to start your ampacity adjustments in accordance with 310.15(B)(2)(a).

Show the engineer the last sentence of 110.14(C)

(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.
Click to expand...

Chris
 
10-4
so am i correct in that there is no correlation between conduit fill calcs.
and temp . rating of terminations? 2 seperate issues all the time?
 
dj94 said:
10-4
so am i correct in that there is no correlation between conduit fill calcs.
and temp . rating of terminations? 2 seperate issues all the time?
Click to expand...


Well, one may lead to the other. In short, you may need to increase your conductor size, which will lead to another set of fill calcs.
 
dj94 said:
10-4
so am i correct in that there is no correlation between conduit fill calcs.
and temp . rating of terminations? 2 seperate issues all the time?
Click to expand...

Yes. Conduit fill requirements are meant to ensure that the conductors can be pulled in without damage. The derating issue is completely separate.
 
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