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    Air Conditioner breaker

    If the condenser label states minimum breaker 21 amps and maximum breaker 35 amps, what awg wire size should be ran to the outside disconnect? What size breaker should be installed in the panel?

    I am getting some confusing statements from an inspector. Please clarify.

    #2
    Originally posted by hardworker View Post
    If the condenser label states minimum breaker 21 amps and maximum breaker 35 amps, what awg wire size should be ran to the outside disconnect? What size breaker should be installed in the panel?

    I am getting some confusing statements from an inspector. Please clarify.
    The nameplate will also tell you the minimum ampacity for the conductors.

    I would be inclined to put in the CB that would be least likely to give me trips. Hint - that would be a 35A CB if one is available for the panel you are powering it from.
    Bob

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      #3
      Originally posted by hardworker View Post
      If the condenser label states minimum breaker 21 amps and maximum breaker 35 amps, what awg wire size should be ran to the outside disconnect? What size breaker should be installed in the panel?

      I am getting some confusing statements from an inspector. Please clarify.
      On something like that it will likely give you that MCA (Minimum Circuit Ampacity) and MOCP (Maximum Over Current Protection). I'd hazard a guess that you are misinterpreting the MCA of 21A as being the "minimum circuit breaker amps", it is not; it is the minimum CIRCUIT amps, meaning you must run conductors rated for a minimum of 21A. Then you calculate the actual wire size based on your other conditions such as voltage drop, number of conductors etc. Once you get your conductor size, then you size the breaker to protect it, but that breaker (or fuses) cannot be larger than 35A.
      __________________________________________________ ____________________________
      Many people are shocked when they discover I am not a good electrician...

      I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

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        #4
        No nameplate would list 21 amps as an overcurrent minimum as there are no 21 amp fuses or breakers. I'm with the others.... 21 amps is the minimum circuit ampacity.

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          #5
          Originally posted by 480sparky View Post
          No nameplate would list 21 amps as an overcurrent minimum as there are no 21 amp fuses or breakers. I'm with the others.... 21 amps is the minimum circuit ampacity.
          that seems likely.
          Bob

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            #6
            For conductors you can use #12 AWG with a 35 amp OCPD if you have conduit and wire or MC cable. If you're using NM cable then you would need #10 AWG
            Rob

            Moderator

            All responses based on the 2017 NEC unless otherwise noted

            Comment


              #7
              Originally posted by 480sparky View Post
              No nameplate would list 21 amps as an overcurrent minimum as there are no 21 amp fuses or breakers. I'm with the others.... 21 amps is the minimum circuit ampacity.
              Yes you are correct I mis-read it. It is 21 amp MCA. Sorry.

              Comment


                #8
                Originally posted by infinity View Post
                For conductors you can use #12 AWG with a 35 amp OCPD if you have conduit and wire or MC cable. If you're using NM cable then you would need #10 AWG
                What happens to the #12awg wire if it pulls 30 amps for some reason and it is protected in the panel with the 35 amp breaker as you suggested? The breaker will not open and the #12 can only carry 20 amps. Please explain this to me for my knowledge.

                Comment


                  #9
                  Originally posted by Jraef View Post
                  ...
                  ...
                  Once you get your conductor size, then you size the breaker to protect it, but that breaker (or fuses) cannot be larger than 35A.
                  Actually, as long as the wiring is presumed to be protected by the motor overload device, you do not have to size the breaker to protect against anything but short circuits and ground faults
                  That means that if your wire, after corrections and adjustments, is rated for say 24A (higher than 21) you can still use a 35A breaker.



                  Sent from my XT1585 using Tapatalk

                  Comment


                    #10
                    Originally posted by GoldDigger View Post
                    Actually, as long as the wiring is presumed to be protected by the motor overload device, you do not have to size the breaker to protect against anything but short circuits and ground faults
                    That means that if your wire, after corrections and adjustments, is rated for say 24A (higher than 21) you can still use a 35A breaker.



                    Sent from my XT1585 using Tapatalk
                    Which is part of the basis for the MOCP listing.

                    But #12 only works for a 21A MCA if you don't need to factor in VD and # of CCCs...
                    __________________________________________________ ____________________________
                    Many people are shocked when they discover I am not a good electrician...

                    I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

                    Comment


                      #11
                      Originally posted by hardworker View Post
                      What happens to the #12awg wire if it pulls 30 amps for some reason and it is protected in the panel with the 35 amp breaker as you suggested? The breaker will not open and the #12 can only carry 20 amps. Please explain this to me for my knowledge.
                      For #12 THHN using the wiring methods in post #6 the conductor ampacity is 25 amps. The unit will not damage those conductors even with a 35 amp OCPD ahead of the branch circuit because the motor itself has integral protection.
                      Rob

                      Moderator

                      All responses based on the 2017 NEC unless otherwise noted

                      Comment

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