User Tag List

Page 2 of 4 FirstFirst 1234 LastLast
Results 11 to 20 of 37

Thread: terminal temperature rating

  1. #11
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
    Posts
    6,042
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I think I'm just going to have to agree to disagree here. Due to other rules in the NEC, mainly 110.14(a) and 240.4(D), #10 THWN-2 can only be loaded to 30A. Regardless of its 40A (or 41.6A here) capacity as a starting point for derating, there's not a single NEC compliant piece of #10 THWN-2 carrying more than 30A, save for the first few moments of a motor starting, welders, etc.

    That #10 in a conduit at 70*F is connected to a load and a source, and even with 90* terminations on both ends, it's still limited to 30A.

    Let me put it another way: short of exceptions in 240.4(e-g), when can a #10 wire actually carry 40A?
    Electricians do it until it Hertz!

  2. #12
    Join Date
    Jan 2009
    Location
    3 Hr 2 Min from Winged Horses
    Posts
    15,950
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Legal?

    "Electricity is really just organized lightning." George Carlin


    Derek

  3. #13
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
    Posts
    6,042
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jumper View Post
    Legal?

    Yes, with conductors that dont fall under the 'small conductor rule' of 240.4(D). Yes, using a size down for a feeder using say 250MCM between the 90*C terminations and 300 or 350MCM from the 75* to 90* terminations is legal provided all conductors are rated for the ampacity at which they are used.

    You could not use say #8 from the 75* to 90* terminations, and #10 from 90 to 90*, if the breaker size was 40A.
    Electricians do it until it Hertz!

  4. #14
    Join Date
    Jan 2009
    Location
    3 Hr 2 Min from Winged Horses
    Posts
    15,950
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Read the question.

    The ampacity of copper # 10 THWN-2 is ____ when there are three current carrying conductors in the conduit and the ambient temperature is 70 degrees F.

    Nothing about loads, breakers, terminals or such.

    Yes, we would consider those things when actually installing but who knows what the person who wrote it factors in. Crappy question by the author IMO.
    "Electricity is really just organized lightning." George Carlin


    Derek

  5. #15
    Join Date
    Apr 2009
    Location
    Williamsburg, VA
    Posts
    6,042
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jumper View Post
    Read the question.

    The ampacity of copper # 10 THWN-2 is ____ when there are three current carrying conductors in the conduit and the ambient temperature is 70 degrees F.

    Nothing about loads, breakers, terminals or such.

    Yes, we would consider those things when actually installing but who knows what the person who wrote it factors in. Crappy question by the author IMO.
    That I can agree with! and yes, we consider the entire code when doing an install. In lieu of pertinent information, how much is one to assume or disregard with a test question like the OP gave? Is the author looking for a table value from 310.16, or 110.14(A), 240.4(D), some combination of, or something else? again, I'll agree with you that it's too vague and crappy.
    Electricians do it until it Hertz!

  6. #16
    Join Date
    Jan 2009
    Location
    3 Hr 2 Min from Winged Horses
    Posts
    15,950
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Let me state it like this:

    The actual ampacity is 40A.

    For correction/adjustments, the calculated ampacity is 41.6A.

    The most commonly used ampacity is 30A.

    Under certain conditions, the permitted ampacity is 35A.
    "Electricity is really just organized lightning." George Carlin


    Derek

  7. #17
    Join Date
    Jul 2003
    Location
    New Jersey
    Posts
    26,335
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jumper View Post
    Let me state it like this:

    The actual ampacity is 40A.

    For correction/adjustments, the calculated ampacity is 41.6A.

    The most commonly used ampacity is 30A.

    Under certain conditions, the permitted ampacity is 35A.
    I agree, if you ask what's the ampacity of a specific conductor you look up the size and insulation type and find the corresponding ampacity in one of the tables in Article 310.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  8. #18
    Join Date
    Jan 2009
    Location
    3 Hr 2 Min from Winged Horses
    Posts
    15,950
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by infinity View Post
    I agree, if you ask what's the ampacity of a specific conductor you look up the size and insulation type and find the corresponding ampacity in one of the tables in Article 310.
    Yep and if your calculations result in a higher ampacity then the actual, you could never use that calculated ampacity to install. 110.14(C)

    At best, one could do that trick above and use the 90C.

    I am hoping whatever answer is in the text reflects that. Using 70F with no other adjustments/corrections was kinda screwy IMO.
    "Electricity is really just organized lightning." George Carlin


    Derek

  9. #19
    Join Date
    Feb 2015
    Location
    Millbrae CA, San Mateo
    Posts
    23
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    let's focus this a bit more

    Thanks to everyone for weighing in. I did not include the Henry's answer. Perhaps it's a good thing I did not, for the posts reveal something that bothers me about this type of question--the answers were all over the place I suspect because the question is so vague. First of all, neither the Henry's nor I asked or said squat about OCPD's. The question is exactly as stated and one of you, i forget which, noted that since the question is simply asking for ampacity, therein lies the reason for defaulting to the 90 degree column. If the query was and only was, what is the ampacity?, then perhaps I could be convinced to go to the 90 degree column. The problem is that since the Henry's supplied additional information---70 degrees F----and then proceeded to answer the question including that information {per table 310.15 B (2) (a)} they are walking down the road of solving the problem as if it were a real world one requiring a thorough and complete application of the code. As I have understood 110.14 C for many years, in accordance with the interpretation of the code in North Carolina, Illinois, Michigan and Pennsylvania, unless you are informed that the terminal temperature rating on both ends is 75 degrees, you have to begin your rating of conductors, regardless of the insulation, in the 60 degree column.

    If the purpose of these tests is to help students prepare for the real world, and not merely word play, then 110.14 C (1) (a) (3) should apply just as does 310.15 B {2) (a).

  10. #20
    Join Date
    Jan 2009
    Location
    3 Hr 2 Min from Winged Horses
    Posts
    15,950
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    What was the answer in the text?
    "Electricity is really just organized lightning." George Carlin


    Derek

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •