adjustment factor help

[S7VEN]

hello, I'm practicing some conductor ampacitie adjustment factors in emt and I would like to know what Iam doing wrong.


for example:


what's the allowable ampacitie of 9 #12 THHN current carrying conductors in a 1/2 EMT?


1/2 EMT - 9 #12 THHN
7-9 Adj. 70%
#12 THHN 90?c - 30 amps


30 x .70% = 21 amps
so good for a 20 amp breaker ?




although the ** by #12 sends you to 240.4(D)
that's only referring to max ocpd
so you still derate at 30 amps correct ?


9 wires in 1/2 allowed 20 amps.
i don't know anybody who would do that..
help ?


thank you

 

[infinity]

Are all 9 conductors considered CCC's? Only the CCC's count towards derating. Yes, you can use the 90? C ampacity for derating purposes you just cannot provide an OCPD that exceeds 240.4(D) unless it falls under 240.4(G).

 

[ActionDave]

9 wires in 1/2 allowed 20 amps.
i don't know anybody who would do that..
help ?


thank you

I would do that, do do that, will continue to do that. Everybody I work with would do that.

I can't think of a good reason not to pull nine 12AWG in a 1/2" emt. What is your concern?

 

[iwire]

I would do that, do do that, will continue to do that. Everybody I work with would do that.

I can't think of a good reason not to pull nine 12AWG in a 1/2" emt. What is your concern?

I am not saying I would never put nine 12s in 1/2" but I would try to avoid it.

In general if it is more than three 12s I run 3/4". Just a few nights ago I had to do three 10 AWGs in EMT and I chose 3/4" Why make it hard?

 

[Smart $]

If it is a straight run or short run with only one 90 bend, 9 #12 THHN conductors isn't too bad to pull. Add bends and [seems like] the difficulty increases exponentially.

Also depends a lot whether there is someone feeding the conductors while another does the pulling. Pulling into a j-box 12 feet off the floor?where the wire rack is?without someone feeding the wire and life becomes unpleasant, at least for a little while. :blink:

 

[infinity]

If using stranded #12's even with 1/2" EMT, 9 conductors isn't a problem.

 

[Smart $]

...
30 x .70% = 21 amps
so good for a 20 amp breaker ?
...

FWIW, you can go as low as 16A and still put it on a 20A breaker, as long as the calculated load is not greater than the maximum adjusted ampacity. However, the next level of adjustment (10-20 conductors) is 50%... which puts you exactly at 15A and you'd have to use a 15A breaker.

BTW, what you are determining is the adjusted ampacity, not the allowable ampacity. The allowable ampacity is the value listed in the table. Correctly stated, the question should have been:

"What's the adjusted ampacity of 9 #12 THHN current carrying conductors in a 1/2 EMT?"

 

[don_resqcapt19]

FWIW, you can go as low as 16A and still put it on a 20A breaker, as long as the calculated load is not greater than the maximum adjusted ampacity. However, the next level of adjustment (10-20 conductors) is 50%... which puts you exactly at 15A and you'd have to use a 15A breaker.

BTW, what you are determining is the adjusted ampacity, not the allowable ampacity. The allowable ampacity is the value listed in the table. Correctly stated, the question should have been:

"What's the adjusted ampacity of 9 #12 THHN current carrying conductors in a 1/2 EMT?"

I don't see a need to add the word adjusted. You are required to adjust the "table" values to find the "ampacity" of those 9 current carrying conductors in the raceway. You may also be required to correct the table values based on temperature, but in both cases you end up with the ampacity of the conductor.

 

[Smart $]

I don't see a need to add the word adjusted. ...

That is correct. There is no need to add the word. But it is still better than using allowable ampacity. If we were to answer the OP question, as stated, from a strictly literal perspective, the answer would be 30A.

However, the question should be worded with adjusted ampacity because it does not exclude there being any correction for temperature.

 

[S7VEN]

Thanks for the help everyone. This is another reason why i picked up the NEC in the first place, can't trust peoples judgement or ways of doing things. In my company the most wire they would pull in an 1/2 EMT would be 1 full boat 3 phase black, red, blue, and white. I understand why they wouldn't want to, but it's unnecessary to refer to the code, when the code allows it. Also I'm a little uncertain of when a neutral is and isn't considered a CCC. For Example:

3 phase 120/208 black red blue neutral - neutral not considered CCC because it carries the unbalanced load?

3 phase 120/208 black red neutral - neutral is or isn't considered CCC?

3 phase 120/208 black neutral - neutral is considered CCC, carrying full load?

1 phase 120/240 black red neutral - neutral isn't considered CCC?

1 phase 120/240 black white - neutral is considered CCC?

thanks to anyone who reads

 

[Smart $]

...

3 phase 120/208 black red blue neutral - neutral not considered CCC because it carries the unbalanced load? Correct

3 phase 120/208 black red neutral - neutral is or isn't considered CCC? Is

3 phase 120/208 black neutral - neutral is considered CCC, carrying full load? Correct

1 phase 120/240 black red neutral - neutral isn't considered CCC? Correct

1 phase 120/240 black white - neutral is considered CCC? Correct

...

Answers red within quote.

 

[S7VEN]

Answers red within quote.

Thanks a lot!

 

[GoldDigger]

Two of three phases, neutral is a CCC.
All of the questions you answered yourself were answered correctly.