Hi, I need help in figuring out how to do the calcuation on conduit size for different size conductors. I have 3'4" EMT and I would like to put 6 #12 THHN's,2#14's,2#8's and 1#10 equipment grounding conductor in this conduit. I have looked in the back of the 05 NEC in table #9 but am confused.I looked in table 5 for the demensions of each conductor. Also looked in table #4 for 3/4" EMT. I am asking for an example on how to do the math. Any help at all please. Thanks Will this combonation of conductors fit in 3'4" EMT?
Conduit Fill Question
- Thread starter elecmen
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Go to Table 5 (in the Chapter 9 Tables), look up the size of THHN conductors (in units of square inches). I see the following:
#12 - .0133
#14 - .0097
#8 - .0366
#10 - .0211
Multiple 6 times .0133, add 2 times .0097, add 2 times .0366, and add .0211, and I get .1935.
Now look at Table 4 (in the Chapter 9 Tables), look up the limit for conductor area for a 3/4 inch EMT (far right column). I see .213.
I conclude that the total area of the proposed conductors is less than the limit, and so therefore the installation is legal. Now, as to how hard it might be to pull that many conductors in the conduit, I have no information to offer.
#12 - .0133
#14 - .0097
#8 - .0366
#10 - .0211
Multiple 6 times .0133, add 2 times .0097, add 2 times .0366, and add .0211, and I get .1935.
Now look at Table 4 (in the Chapter 9 Tables), look up the limit for conductor area for a 3/4 inch EMT (far right column). I see .213.
I conclude that the total area of the proposed conductors is less than the limit, and so therefore the installation is legal. Now, as to how hard it might be to pull that many conductors in the conduit, I have no information to offer.
according to table 4...
according to table 4...
3/4" EMT has a total area of .533 in^2
6 #12 thhn's have a total area of .0133*6=.0798in^2
2 #14 thhn's have a total area of .0097*2=.00194in^2
2 #8 thhns's have a total area of .0507*2=.1014in^2
1 #10 thhn has a total area of .0211in^2
so the total area of your conductors in inches^2 is 0.20618, and since you are using over 2 wires, you are only permitted to occupy 40% of the total area of the conduit which is 0.213. So by code, you are just on the OK side of too many, but on the practical side, you probably will have some trouble pulling it. Is stepping up to 1" or even 1 1/4" an option?
Someone please correct me if there is error in my findings...
Use plenty of lube!
according to table 4...
3/4" EMT has a total area of .533 in^2
6 #12 thhn's have a total area of .0133*6=.0798in^2
2 #14 thhn's have a total area of .0097*2=.00194in^2
2 #8 thhns's have a total area of .0507*2=.1014in^2
1 #10 thhn has a total area of .0211in^2
so the total area of your conductors in inches^2 is 0.20618, and since you are using over 2 wires, you are only permitted to occupy 40% of the total area of the conduit which is 0.213. So by code, you are just on the OK side of too many, but on the practical side, you probably will have some trouble pulling it. Is stepping up to 1" or even 1 1/4" an option?
Someone please correct me if there is error in my findings...
Use plenty of lube!
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LarryFine
Master Electrician Electric Contractor Richmond VA
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Let us not forget about derating for those 10 CC conductors.
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- Lockport, IL
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- Retired Electrical Engineer
Table 310.15(B)(2)(a). You have 10 current-carrying conductors in the same raceway, so you must derate the ampacity of each by 50%. Please note that you may start with the rating in the 90C column, before applying the 50% factor.
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sparkydon,
No that cannot be assumed. Only an engineer can use the tables in Annex B.
Don
chris kennedy
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charlie b said:
Details please. I've always derated from the 75 col.
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That is certainly allowed too, but it is unnecessary. See the second sentence of 110.14(C). I concede that that sentence is not written as clearly as one could wish. But what it says to me is that if I use a conductor with 90C insulation, then I can apply the derating factors (i.e., ambient over 30C and more than three current-carrying conductors) to the values in the 90C column. My final answer for ampacity cannot be higher than the value in the 75C column, but I don't have to start there.chris kennedy said:
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It is not defined, not in the NEC, and not in any of the college textbooks I keep at my desk. That is part of the problem, and it is the reason I wish the NEC did not include that phrase. People will want to take advantage of the tables that apply a "load diversity," but there is no easy way to prove that it is applicable.sparkydon said:
One possible sense of that phrase could be applied to a situation in which you have the conductors feeding several motors in a single conduit, and in which an interlock system prevents all the motors from running at the same time. But there is some disagreement regarding whether an interlock is necessary.
chris kennedy
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charlie b said:
Of course. Seems perfectly clear to me.
RUWIREDRITE
Senior Member
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- PA, Business' in NJ/PA
conduit fill
conduit fill
one interseting factor about this question is what are the conductors for, feeds, neutrals,controls ,egc? this might change your derating factors, but as stated above a larger conduit can make the wire pull easier even with some pulling soap.
conduit fill
one interseting factor about this question is what are the conductors for, feeds, neutrals,controls ,egc? this might change your derating factors, but as stated above a larger conduit can make the wire pull easier even with some pulling soap.
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If this is a short straight run you may not have a problem pulling wires but if you have 2 or 3 90's-- gulp. Also, I believe if you conduit is less than 2 feet then you do not have to derate.
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Dennis Alwon said:
That is true and the permitted amount of fill goes up to 60%.
RRelec
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When using 110.14(C) & derating from the 90C column, don't forget to look at 110.14(C)(1). As in the OP, I would assume 110.14(C)(1)(a)(2) applies.
Quote:
"My final answer for ampacity cannot be higher than the value in the 75C column, but I don't have to start there."
Please correct me if I'm wrong, I assume the 75C would be 60C, in regards to the OP.
Disclaimer:
I'm just stating this for clarification and informational purposes only.
R
Quote:
"My final answer for ampacity cannot be higher than the value in the 75C column, but I don't have to start there."
Please correct me if I'm wrong, I assume the 75C would be 60C, in regards to the OP.
Disclaimer:
I'm just stating this for clarification and informational purposes only.
R
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RRelec said:
This is 90 degree C conductor, THHN, in a conduit. The 60 degree C column would come into play at the terminations if they were rated for 60 degrees C.
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