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    110.15(C)(1) confusion

    Hi,

    I'm getting myself all jammed up on this section 110.15(C)(1)

    How does this section jive with 310.15(B)(16)?

    For instance, I'm looking to install a 100 amp sub-panel to a detached pool house on a single family dwelling. I was looking at the equipment and saw that my circuit breaker is rated for 75C and thought that I can use #3 THHN then I started reading elsewhere that because of 110.15(C)(1) that I have to abide by 60C. So I need help understanding if I'm reading the code correctly.

    Not to mention the confusion of the grounding conductor I thought should be #8 according to the NEC but read that it should be #6 or even #4 and now I've just got myself all confused.

    Why is the code so confusing?

    #2
    What year are you looking at?

    Comment


      #3
      2014 and I have the 2017

      Comment


        #4
        110.15(C)(1) ???
        At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

        Comment


          #5
          that's exactly how confused I am. 110.14(C)(1)

          specifically
          "Termination provision of eqipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only of the following:

          (1) Conductors rated 60C

          Do I have always have to size wires to 60C if they are 14 AWG to 1 AWG?
          Or if I have 75C wire and a 75C circuit breaker can I use that column of 310.15(B)(16)?

          Comment


            #6
            Originally posted by prattz99 View Post
            that's exactly how confused I am. 110.14(C)(1)

            specifically
            "Termination provision of eqipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only of the following:

            (1) Conductors rated 60C

            Do I have always have to size wires to 60C if they are 14 AWG to 1 AWG?
            Or if I have 75C wire and a 75C circuit breaker can I use that column of 310.15(B)(16)?
            The key is in C1: "Unless equipment is listed and marked otherwise...."

            If you don't have the equipment and label right in front of you, my understanding is that its pretty safe to assume modern equipment has a 75 degree rating, even for equipment under 100 amps.

            Comment


              #7
              Originally posted by steve66 View Post
              The key is in C1: "Unless equipment is listed and marked otherwise...."

              If you don't have the equipment and label right in front of you, my understanding is that its pretty safe to assume modern equipment has a 75 degree rating, even for equipment under 100 amps.
              Unless that equipment is more then 30 years old, it likely has 75C terminal ratings. You generally only need to use 60C ampacity with older equipment, older conductors that were only 60C, or with NM or (some) SE cable applications.
              I live for today, I'm just a day behind.

              Comment


                #8
                Okay great, so I've been using 310.15(B)(16) correctly then?

                A breaker rated at 75C I can then use #3THHN copper rated at 90C I've within the NEC to fuse it for 100 amps. Good to go?

                Comment


                  #9
                  Originally posted by prattz99 View Post
                  Okay great, so I've been using 310.15(B)(16) correctly then?

                  A breaker rated at 75C I can then use #3THHN copper rated at 90C I've within the NEC to fuse it for 100 amps. Good to go?
                  Generally yes, but you do have a burden of proof to confirm that the equipment on both sides is "listed and labeled otherwise" for 75C, if you are questioned on it. It is a rare scenario that recently manufactured equipment isn't listed and labeled otherwise for 75C.

                  Comment


                    #10
                    Originally posted by prattz99 View Post
                    Okay great, so I've been using 310.15(B)(16) correctly then?

                    A breaker rated at 75C I can then use #3THHN copper rated at 90C I've within the NEC to fuse it for 100 amps. Good to go?
                    Careful how you interpret what you just said. #3THHN is rated for 90C, and you can use 90C ampacity as the starting basis for ampacity adjustments - but after adjustments are applied you still must have a conductor no smaller then what is listed in the 75C column of the table because of the 75C termination rating.
                    I live for today, I'm just a day behind.

                    Comment


                      #11
                      Originally posted by prattz99 View Post
                      Okay great, so I've been using 310.15(B)(16) correctly then?

                      A breaker rated at 75C I can then use #3THHN copper rated at 90C I've within the NEC to fuse it for 100 amps. Good to go?
                      With 75° C terminations at both end #3 THHN has an ampacity of 100 amps so you're code complaint. Even if you used a 75° C conductor like THWN it would still be rated for 100 amps.
                      Rob

                      Moderator

                      All responses based on the 2017 NEC unless otherwise noted

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