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Why 15A for #14, 20A for #12, and 30A for #10?

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    #31
    As Curley once said "Cause there's no bones in ice cream.
    Bob O.84,Pa.15330

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      #32
      Originally posted by Pierre C Belarge
      Here is a bulletin from SQD that may shed some light on the topic.

      http://ecatalog.squared.com/pubs/Ele...B9901R2-02.pdf
      Thanks for the article, it has some good info. Unfortunately, they do not discuss why the smaller conductors are limited in current carrying capacity lower then the value provided in NEC T310.16.

      For conservatism, I will accept that I should use the 60 deg C column for ampacity on #14, #12, and #10 wire, regardless of the actual temp rating of the insulation. With that said, I have a 20A breaker, and I am going to only load it to 80%. T310.16 says #14 is good for 20A, and there cannot be more then 16A load on the circuit, which matches my breaker. (I can always size up to the next standard size = 20A) I meet all code requirements, "EXCEPT" that the NEC says I have to limit #14 AWG to 15A, WHY, WHY, WHY, WHY, WHY...????????????????????

      This makes no sense!
      "Just because you're paranoid, doesn't mean they're not out to get you"

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        #33
        Sometimes rules is rules.
        I may not agree with the 30 mph speed limit in an area of open road, but it is still the speed limit.

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          #34
          Originally posted by kingpb
          Thanks for the article, it has some good info. Unfortunately, they do not discuss why the smaller conductors are limited in current carrying capacity lower then the value provided in NEC T310.16.

          For conservatism, I will accept that I should use the 60 deg C column for ampacity on #14, #12, and #10 wire, regardless of the actual temp rating of the insulation. With that said, I have a 20A breaker, and I am going to only load it to 80%. T310.16 says #14 is good for 20A, and there cannot be more then 16A load on the circuit, which matches my breaker. (I can always size up to the next standard size = 20A) I meet all code requirements, "EXCEPT" that the NEC says I have to limit #14 AWG to 15A, WHY, WHY, WHY, WHY, WHY...????????????????????

          This makes no sense!
          The world may never know.

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            #35
            Originally posted by kingpb
            . . . there cannot be more then 16A load on the circuit . . .
            Actually, there certainly can. There may not be more than 80% load continuously applied, but the rules have no more power over abuse than a stop sign has over a moving vehicle.

            As Jon said back in: http://forums.mikeholt.com/showpost....4&postcount=16,
            Originally posted by winnie
            For the same _percentage_ overload, smaller conductors will heat up and overheat faster than larger conductors.
            Think of which circuits in your home you could fully load, or overload, without a malfunction of equipment, through normal use.
            Master Electrician
            Electrical Contractor
            Richmond, VA

            Comment


              #36
              Originally posted by kingpb
              . . . WHY, WHY, WHY, WHY, WHY...????????????????????
              Originally posted by Agent Smith

              "Why, Mr. Anderson? Why do you do it? Why get up? Why keep fighting? Do you believe you're fighting for something? For more that your survival? Can you tell me what it is? Do you even know? Is it freedom? Or truth? Perhaps peace? Yes? No? Could it be for love? Illusions, Mr. Anderson. Vagaries of perception. The temporary constructs of a feeble human intellect trying desperately to justify an existence that is without meaning or purpose. And all of them as artificial as the Matrix itself, although only a human mind could invent something as insipid as love. You must be able to see it, Mr. Anderson. You must know it by now. You can't win. It's pointless to keep fighting. Why, Mr. Anderson? Why? Why do you persist?"
              ~ The Matrix Revolutions
              Master Electrician
              Electrical Contractor
              Richmond, VA

              Comment


                #37
                May be on to something.......

                persist - To hold firmly and steadfastly to a purpose, state, or undertaking despite obstacles, warnings, or setbacks.

                So, in that regard the quest continues, and low and behold, under the right rock-

                According to the technical folks at Southwire, although they do not have anything in writing, the word is UL tested circuit breakers - 15, 20 and 30A as a system using #14, 12 and 10 Awg wire. UL found that when testing a #14 on a 20 amp breaker, there were problems with the breaker not operating properly. The same thing occurred with the #12 on a 30 amp breaker.

                Supposedly the heating of the wire would cause the breaker to over heat, which in turn would cause the wire temperature to rise, leading to the breaker temperature rising....... so, to combat this oddity, UL simply put a limit on the conductor ampacity to resolve the problem, instead of trying to understand what was really happening.

                I will continue to try and confirm this, and possibly get something in writing.
                "Just because you're paranoid, doesn't mean they're not out to get you"

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