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What is the ampacity for 8 AWG wire? 50 or 40

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    #16
    One o the things used to irk me at a previous place of employment was the justification for doing something a particular way was often "we have been doing it that way for 40 years". My response was generally along the lines of "about time we started doing it right then".
    Bob

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      #17
      I had been "doing it that way" for years also.

      I only recently learned that while #8 SE is good for 50 amps, # 8 Romex is not.

      Lame.

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        #18
        Originally posted by JohnConnolly
        ...#8 SE is good for 50 amps...
        How do you figure? :confused:

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          #19
          Originally posted by georgestolz
          How do you figure? :confused:

          If both the SE and NM were copper the #8 SE could be used at 75 degrees C or 50 amps. The #8 NM at 60 degrees C or 40 amps.
          Rob

          Moderator

          All responses based on the 2017 NEC unless otherwise noted

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            #20
            Originally posted by infinity
            If both the SE and NM were copper the #8 SE could be used at 75 degrees C or 50 amps. The #8 NM at 60 degrees C or 40 amps.

            Yeah....what he said.

            A customer called me on it once about 5 years ago and I looked it up. He was right as far as I could tell. That code lingo really confuses me.

            When I started wiring, we didn't HAVE #8 NM, it was all SE style. I assumed for years that #8= 50 amps.

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              #21
              http://www.iaei.org/subscriber/magaz...d_hartwell.htm

              Saludos
              5 out of 10 people watching the TV... are 50%

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                #22
                Originally posted by Fer Lefer

                I see a lot of words but did you answer his question?

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                  #23
                  The NFPA gave me a disclaimed opinion once that you must go by worst-case temperature derating. Why they think this is a 30C/86F world is beyond me. Attics can easily hit 140+ F. It was 116F in Vegas last week. I can't imagine an attic there.

                  Personally I think they should make the nominal table ratings for 50C/122F, and make a new derate table from there, that way those who miss this key point will still have something closer to safely designed.

                  THERE'S NO LAW AGAINST FATTER WIRES other than cost and maybe it won't fit on the terminals. It's cheaper than what the fire will cost.

                  I won't get started on how many motors I've had where the terminals are two or more wire sizes smaller than their UL listed current rating requires.

                  Matt

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                    #24
                    Originally posted by JohnConnolly
                    I see a lot of words but did you answer his question?
                    And you had to quote them all!!!!!

                    Didn't I answer? My fault: you need, at least a 4AWG or a 6AWG40A if it feeds a non-continuous load, or 40/1.25 = 32A52.8A

                    :grin: Served!
                    5 out of 10 people watching the TV... are 50%

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                      #25
                      You can't really properly answer the question since he didn't say what the 50 ampere rating is. Is this the MCA or the maximum OCPD size?
                      Rob

                      Moderator

                      All responses based on the 2017 NEC unless otherwise noted

                      Comment


                        #26
                        Originally posted by infinity
                        You can't really properly answer the question since he didn't say what the 50 ampere rating is. Is this the MCA or the maximum OCPD size?
                        I bet its the maximum breaker, and the minimum is a 25 amp breaker... so # 10 THHN would be fine... but it's just a guess since I can't see the damn thing...
                        Last edited by stickboy1375; 07-10-07, 08:34 PM.
                        "Electricity is actually made up of extremely tiny particles called electrons, that you cannot see with the naked eye unless you have been drinking."

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                          #27
                          Isn't 52.8 more than 50?



                          Don't answer, I'll just get more confused.

                          I am going to take up drywall so I don't have to think anymore.

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                            #28
                            Originally posted by JohnConnolly
                            Isn't 52.8 more than 50?



                            Don't answer, I'll just get more confused.

                            I am going to take up drywall so I don't have to think anymore.

                            You're basing this on the assumption that were talking about the maximum OCPD and not the minimum conductor ampacity. For AC units the MCA is used to size the conductors not the max OCPD.
                            Rob

                            Moderator

                            All responses based on the 2017 NEC unless otherwise noted

                            Comment


                              #29
                              hmm...I have seen this question before...lol....This unit should have a nameplate on it with the Mininum circuit size and maximum OCPD size listed on it.
                              Last edited by radiopet; 07-11-07, 07:44 AM.

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                                #30
                                Originally posted by JohnConnolly
                                Isn't 52.8 more than 50?.
                                Yes

                                Originally posted by JohnConnolly
                                Don't answer, I'll just get more confused.

                                I am going to take up drywall so I don't have to think anymore.
                                :smile: "Yes": a confusing answer. :smile:
                                5 out of 10 people watching the TV... are 50%

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