Fred S
New member
- Location
- Plainfield,NJ USA
Ho many #10 THHN wires allowed in 1 inch emt after derating for 20 amp circuits all seprate nuetrals
conduit fill
- Thread starter Fred S
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Welcome
Your question sounds as if it is test question and as such we prefer you tell what you think the answer is and briefly how you determined that answer and any number of folks will be glad to help.
Roger directed you to a starting point.
Your question sounds as if it is test question and as such we prefer you tell what you think the answer is and briefly how you determined that answer and any number of folks will be glad to help.
Roger directed you to a starting point.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Here's another hint fill has nothing to do with ampacity. The purpose of the fill restrictions are to keep the conductors from being damaged during installation.
JFletcher
Senior Member
- Location
- Williamsburg, VA
Welcome to the forum.
If he wanted to use 30A breakers, that would be more limiting than the pipe size. It's irrelevant here but the OP needs to be able to figure out why.
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Here's another hint: the maximum number of #10 CCC that can be compliantly installed in a 1" EMT conduit is less than the number that would bring your allowable OCPD to less than 20A due to derating. and yet another hint: online tables vary a bit and may give you an incorrect answer.
If he wanted to use 30A breakers, that would be more limiting than the pipe size. It's irrelevant here but the OP needs to be able to figure out why.
~~~~~~~~~~~~~~~~~~~~~~~
Here's another hint: the maximum number of #10 CCC that can be compliantly installed in a 1" EMT conduit is less than the number that would bring your allowable OCPD to less than 20A due to derating. and yet another hint: online tables vary a bit and may give you an incorrect answer.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I think that you read the question incorrectly :"Ho many #10 THHN wires allowed in 1 inch emt"?
I don't want to confuse the OP (if he comes back) but I see where JFlecther is coming from. One should take the derating factor from the question into account to see if it's relevant or not. I originally thought it would be.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I'm curious as to why? The thread title is "conduit fill" and the question is "Ho many#10 THHN wires allowed in 1 inch emt".
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
It does not stop there---the question continues with after derating for a 20 amp circuit. I assume the separate neutrals refers to 120v circuits and that the neutrals shall be counted as current carrying conductor's.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
So the question is not about maximum conduit fill it's about how many #10s can you put in the raceway. To my point the second part is irrelevant because the answer is the same the derating doesn't change a thing.
So the question is not about maximum conduit fill it's about how many #10s can you put in the raceway. To my point the second part is irrelevant because the answer is the same (IF) the derating doesn't change a thing.
I think the clue would be to add "If" to your statement as I have above.
One needs to realize that it is permissible to use the 90° column. As JFletcher points out the answer would not be the same using 30 amp breakers nor would it be the same using THHW is a wet location.
I can easily see that as a test question to challenge one.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Agreed but why would you add all of these variables into a simple question? The information given is 1" EMT, #10 THHN and 20 amp circuits with separate neutrals. Can the question not be answered with what's in bold?
JFletcher
Senior Member
- Location
- Williamsburg, VA
It can be but using the aforementioned table 310.15(b)(3)(a) alone is insufficient in determining the answer. It's only correct in this case because you've done the mental math to know you'd need 21+ CCC to drop #10 THHN derating below 20A OCPD and you cant fit 21 #10s in a 1" EMT conduit. The fill is the limiting factor here, not the derating, but both must be used to arrive at a correct answer.
Fred: there's another hint. Answer is less than 21.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
My simple point is that if this were a test question, however poorly it's written, could you answer the question given the information provided?
sure. ,, but since the question went beyond "how many" and introduced derating if you did not know how to apply derating vs the 75° and 90° columns you could come up with an incorrect answer.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Where does 75° C come into play with the stated conductor insulation type of THHN?
And the test would assume the student already knew that information or how to go about finding it. The "how many" and "derating" parts would be the same for any size conduit that could accommodate enough #10 CCC's to mandate the reduction in ampacity.
Roger
JFletcher
Senior Member
- Location
- Williamsburg, VA
Yes I can. My point is that your initial post:
While technically correct could lead to an incorrect answer to the question Fred posed if one did not also consider ampacity adjustments. That they do not come into play here does not mean they can be ignored. If the thread title was "Question?" instead of "conduit fill", would that help you see my point?
Take the exact same question Fred asked, make it this:
"How many #10 THHN wires allowed in 1 inch emt after derating for 30 amp circuits all separate neutrals"
Is that question answerable? and is the answer different than for 20A? yes and yes.
Fill very much has something to do with ampacity because if you put 12 #10 CCC in a 1" EMT conduit on 30A breakers you are going to fail your inspection.
It doesn't and you and I know that, From teaching my course, IF I asked that question I guarantee some student would miss the question by performing some sort of derating. From the tests I have taken it's important to know what to ignore...
"You got to know when to hold 'em and when to fold 'em"
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