N.E.C 2008 code classes

[Eric R 1973]

Recently in my class an argument has risen over this ques. What is the allowable ampacity of a #12 THHN conductor run in a raceway with 8 other current carrying conductors, in an ambient temp. of 94 degrees F, And connected to a device that has 75-degree terminations?
(a)16.8A (b)16.45A (c) 20.16A (d)30A

I just finished the course today with a 93 avg. so i'm not trying to cheat on an exam. Isay its (a) one of my instructors agreed another says (c)
so wht are your thoughts?

 

[infinity]

The answer is C. The 75? is irrelevant.

30 amps
9 CCC's=70%
.96 Correction Factor

30 * 70% * .96 = 20.16

 

[charlie b]

I agree with Rob, except that I would not dismiss the 75C as being irrelevant. If turns out not to influence the final answer this time, but with other sets of numbers it might.

The only way I can get to the answer of 16.8 amps is to use the ampacity of 25 amps from column B, and the temperature adjustment factor of 0.96 from column C. If that is what you did, then I would ask why you used information from two different columns.

Now if I had written the exam, I might have been cruel and sadistic by putting 20 amps as a possible answer. It would be a wrong answer, but it could easily fool the unwary. True, we cannot protect this wire above 20 amps, but the "ampacity" is still 20.16.

 

[infinity]

I agree with Rob, except that I would not dismiss the 75C as being irrelevant. If turns out not to influence the final answer this time, but with other sets of numbers it might.

The only way I can get to the answer of 16.8 amps is to use the ampacity of 25 amps from column B, and the temperature adjustment factor of 0.96 from column C. If that is what you did, then I would ask why you used information from two different columns.

Now if I had written the exam, I might have been cruel and sadistic by putting 20 amps as a possible answer. It would be a wrong answer, but it could easily fool the unwary. True, we cannot protect this wire above 20 amps, but the "ampacity" is still 20.16.

I should have said irrelevant to this calculation. It's likely that this is just some information thrown in there to confuse you.

 

[gndrod]

16.8

16.8

The only way I can get to the answer of 16.8 amps is to use the ampacity of 25 amps from column B, and the temperature adjustment factor of 0.96 from column C. If that is what you did, then I would ask why you used information from two different columns.


He was probably using Al wire. 70% x 25 (Al 90C derate) x .96

 

[cripple]

N.E.C-2008-code-classes

N.E.C-2008-code-classes

If the question stated what is the allowable ampacity of a 12 AWG conductor the right answer would (c), but if it is asking what is the maximum ampacity permitted of the branch-circuit conductors of a designed load on a 20 amp circuit then (a) would correct. Table 310.16 (2008) is what we use to determine the allowable ampacity of conductors for any load.

 

[gndrod]

If the question stated what is the allowable ampacity of a 12 AWG conductor the right answer would (c), but if it is asking what is the maximum ampacity permitted of the branch-circuit conductors of a designed load on a 20 amp circuit then (a) would correct. Table 310.16 (2008) is what we use to determine the allowable ampacity of conductors for any load.

My apologies. Charlie b answered that and I jumped in trying to inject a little humor to 16.8.

 

[dana1028]

If the question stated what is the allowable ampacity of a 12 AWG conductor the right answer would (c), but if it is asking what is the maximum ampacity permitted of the branch-circuit conductors of a designed load on a 20 amp circuit then (a) would correct.

Nobody jumped on this?

Since when is the maximum allowable ampacity of a 20A circuit 16.8 amps?

You are allowed 20A on a 20A circuit...you are limited to 16A for a continuous load.

 

[gndrod]

20 vs 16.8

20 vs 16.8

Nobody jumped on this?

Since when is the maximum allowable ampacity of a 20A circuit 16.8 amps?

You are allowed 20A on a 20A circuit...you are limited to 16A for a continuous load.

Hi Dana,
No one jumped on this because the OP question related to 12Awg allowable ampacity for 8 conductor bundling adjustment at 94C ambient and not the ampacity of a 20A circuit. Whether the conductors were CU or Al were not mentioned. Accordingly, there could be two answers without assumptions...
a) 16.8 is correct for Al.... c) 20.16 is correct for Cu.

I hope this clears up the confusion.

 

[gndrod]

Whoops

Whoops

change to 94F