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AFCI required on MWBC?

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    #31
    Originally posted by jap View Post
    A multiwire branch circuit is not a 120v circuit.

    JaP>
    Originally posted by jaggedben View Post
    Have you been able to argue this successfully with an AHJ?
    It is a 120/240 volt circuit, 120/208 and 277/480 are pretty common also.

    New loophole to get out of using AFCI's - only run MWBC's, and claim they are not "120 volt circuits"
    I live for today, I'm just a day behind.

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      #32
      Originally posted by infinity View Post
      210.12(A) says all 120 volt circuits, if you run MWBC for two 120 volt circuits then it requires AFCI protection.
      Sure. But the Article 100 definition of "Voltage, nominal" says:

      Voltage, Nominal. A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts).
      So the argument would be that a MWBC may be considered to be one 120/240 circuit, rather than two 120 volt circuits. Let's say that every outlet on the circuit has both ungrounded conductors present, along with the neutral.

      Cheers, Wayne

      Comment


        #33
        Originally posted by infinity View Post
        210.12(A) says all 120 volt circuits, if you run MWBC for two 120 volt circuits then it requires AFCI protection.
        I admit I have never thought of this, nor ever heard of the interpretation/philosophy of MWBC's being exempt from AFCI, but see the ambiguity now. Consider a NEMA 14-20 recep (as someone mentioned a few pages back). Does that need aFCI? I say no. But then I also say that it follows that a MWBC's doesnt require AFCI UNTIL it splits in to two 120V circuits.
        Ethan Brush - East West Electric. NY, WA. MA

        "You can't generalize"

        Comment


          #34
          Originally posted by electrofelon View Post
          I admit I have never thought of this, nor ever heard of the interpretation/philosophy of MWBC's being exempt from AFCI, but see the ambiguity now. Consider a NEMA 14-20 recep (as someone mentioned a few pages back). Does that need aFCI? I say no. But then I also say that it follows that a MWBC's doesnt require AFCI UNTIL it splits in to two 120V circuits.
          How often is a 14-20 used in the rooms mentioned in 210.12? Mostly only used at a dwelling as a standby generator inlet and that is about it, and not typically in any the rooms mentioned in 210.12 either.
          I live for today, I'm just a day behind.

          Comment


            #35
            Originally posted by kwired View Post
            How often is a 14-20 used in the rooms mentioned in 210.12?
            How long have you been on this forum? Its what we do here is come up with the most bizarre and unlikely things to debate and prove how poorly worded the code is
            Ethan Brush - East West Electric. NY, WA. MA

            "You can't generalize"

            Comment


              #36
              Originally posted by electrofelon View Post
              How long have you been on this forum? Its what we do here is come up with the most bizarre and unlikely things to debate and prove how poorly worded the code is
              I know, I suggested there is a loophole in using only MWBC's to avoid needing AFCI's - but I know that won't go over very well even if you have pretty convincing justification prepared.
              I live for today, I'm just a day behind.

              Comment


                #37
                Originally posted by kwired View Post
                It is a 120/240 volt circuit, 120/208 and 277/480 are pretty common also.
                You just had to let the cat out of the bag didn't you?

                Jap>

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                  #38
                  Originally posted by jap View Post
                  You just had to let the cat out of the bag didn't you?
                  Well, meow is as good a time as any.
                  Master Electrician
                  Electrical Contractor
                  Richmond, VA

                  Comment


                    #39
                    If a 20 amp small appliance multi wire branch circuit is not two branch circuits than thousands of kitchens have been wired in violation and passed inspection by thousands of inspectors for 50 plus years

                    interesting no one questioned that application for years, now that AFCI protection is a requirement all of a sudden a multi wire circuit for the same application is no longer two 120 volt branch circuits

                    Not a logical argument and seems self serving

                    Comment


                      #40
                      Originally posted by david View Post
                      If a 20 amp small appliance multi wire branch circuit is not two branch circuits than thousands of kitchens have been wired in violation and passed inspection by thousands of inspectors for 50 plus years

                      interesting no one questioned that application for years, now that AFCI protection is a requirement all of a sudden a multi wire circuit for the same application is no longer two 120 volt branch circuits

                      Not a logical argument and seems self serving
                      My argument exactly.
                      Rob

                      Moderator

                      All responses based on the 2017 NEC unless otherwise noted

                      Comment


                        #41
                        I guess 12-2-2 is the fix now....~RJ~

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                          #42
                          I'm glad I didn't do residential work.

                          Comment


                            #43
                            Originally posted by kwired View Post
                            New loophole to get out of using AFCI's - only run MWBC's, and claim they are not "120 volt circuits"
                            That would be a great loophole, except you wouldn't be able to install any 15A or 20A, 125V receptacles on the circuit, so the loophole is self defeating.

                            Comment


                              #44
                              Originally posted by david View Post
                              If a 20 amp small appliance multi wire branch circuit is not two branch circuits than thousands of kitchens have been wired in violation and passed inspection by thousands of inspectors for 50 plus years
                              The beauty of 210.4(A) is that it gives us a choice. If we run a single MWBC for the small appliance branch circuits, and we want to consider it as two 120V circuits for compliance with 210.11(C)(1), great. Then the two circuits will need to comply with 210.12.

                              But if you buy the idea that an MWBC considered as a single 120/240 circuit does not need to comply with 210.12, all that means is that to avoid needing to AFCI the small appliance branch circuits, you'd need to run two MWBCs for them.

                              No contradiction between the proposed interpretation and past practice.

                              Cheers, Wayne

                              Comment


                                #45
                                Originally posted by david luchini View Post
                                That would be a great loophole, except you wouldn't be able to install any 15A or 20A, 125V receptacles on the circuit, so the loophole is self defeating.
                                Sorry, where is the prohibition on installing a 125V receptacle on a 120/240V branch circuit? If there is one, I agree it would sink this line of thought.

                                Cheers, Wayne

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