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110.3B vs 725.48(A)

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    110.3B vs 725.48(A)

    I have a vendor device that has ONE conduit hub for the following circuits: 120VAC power, 24VDC discreet signal (customer supplied cable) and 1900VDC (vendor supplied cable) through the same conduit into the vendor supplied enclosure. The vendor supplied cable is insulated at 1900VDC/600VAC. The other two cables are customer supplied, insulated at 600VAC. All cables are functionally associated, but is this a violation of 725.48(A)? Or does 110.3B permit this since its a vendor design and listed device?

    #2
    My initial reaction is to say that if it is listed in the condition you describe, we don't have to question what goes inside the conduit or the enclosure. However, there is a general notion that conductors in the same conduit have to have the insulation rating of the highest voltage system in the set. What I don't know is how DC and AC voltage ratings are associated with one another. I believe the rule is intended to protect against the possibility that damage to the highest voltage conductor (perhaps during installation) could result in leakage current that exceeds the rating of a nearby conductor. If that second conductor has a lower voltage rating, then leakage current could pass into the second conductor, causing all kinds of unpleasantries. So I can't say that I would approve the installation. If the 24VDC and 120VAC conductors have insulation ratings in excess of 1900VDC (you didn't say that they did), then I would call this OK.
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

    Comment


      #3
      Thanks Charlie. Would it matter if the vendor supplied cable, i.e. 1900VDC is shielded in terms of mitigating leakage current into the lesser insulated cables?

      Comment


        #4
        Originally posted by Isaiah View Post
        Thanks Charlie. Would it matter if the vendor supplied cable, i.e. 1900VDC is shielded in terms of mitigating leakage current into the lesser insulated cables?
        I'm not sure that would matter in the context of mixing different voltages in the same raceway that you are concerned about. However, one thing you said could make all this OK.

        "I have a vendor device that has ONE conduit hub for the following circuits: 120VAC power, 24VDC discreet signal (customer supplied cable) and 1900VDC (vendor supplied cable) through the same conduit into the vendor supplied enclosure."

        If the vendor instructions and supplied materials instruct you to install the unit that way then I would assume it was approved.

        -Hal

        Comment


          #5
          Originally posted by charlie b View Post
          My initial reaction is to say that if it is listed in the condition you describe, we don't have to question what goes inside the conduit or the enclosure. However, there is a general notion that conductors in the same conduit have to have the insulation rating of the highest voltage system in the set. What I don't know is how DC and AC voltage ratings are associated with one another. I believe the rule is intended to protect against the possibility that damage to the highest voltage conductor (perhaps during installation) could result in leakage current that exceeds the rating of a nearby conductor. If that second conductor has a lower voltage rating, then leakage current could pass into the second conductor, causing all kinds of unpleasantries. So I can't say that I would approve the installation. If the 24VDC and 120VAC conductors have insulation ratings in excess of 1900VDC (you didn't say that they did), then I would call this OK.
          Charlie, I would just clarify/emphasize that this is for "conductors" ( which is indeed the term you used). The code reference for under 600 volts is 300.3(C)(1), over 600 volts is (C)(2). OP did use the word "cables". IMO those sections do not apply to conductors in cable assemblies.
          Ethan Brush - East West Electric. NY, WA. MA

          "You can't generalize"

          Comment


            #6
            Originally posted by electrofelon View Post

            Charlie, I would just clarify/emphasize that this is for "conductors" ( which is indeed the term you used). The code reference for under 600 volts is 300.3(C)(1), over 600 volts is (C)(2). OP did use the word "cables". IMO those sections do not apply to conductors in cable assemblies.

            300.3(C)(2) covers cables:
            Over 1000 Volts, Nominal. Conductors of circuits rated
            over 1000 volts, nominal, shall not occupy the same equipment
            wiring enclosure, cable, or raceway with conductors of circuits
            rated 1000 volts, nominal, or less unless otherwise permitted in
            300.3(C)(2)(a) through 300.3(C)(2)(d).

            What is this thing? even a link to the UL listed cable would be handy.
            If you have a significant amount of 1900V your also in article 490 territory.


            Comments based on 2017 NEC unless otherwise noted.

            Comment


              #7
              Originally posted by tortuga View Post
              300.3(C)(2) covers cables:
              The OP's situation would not have the differing voltages occupying the same cable.

              That rule is about conductors sharing a conduit or a cable, not cables sharing a conduit.

              The big question is whether conductors = cables. I say not.
              Master Electrician
              Electrical Contractor
              Richmond, VA

              Comment


                #8
                Originally posted by LarryFine View Post

                The OP's situation would not have the differing voltages occupying the same cable.

                That rule is about conductors sharing a conduit or a cable, not cables sharing a conduit.

                The big question is whether conductors = cables. I say not.
                You know, I missed that! I was thinking conductors (thanks Charlie), and Larry, you are absolutely right, conductors are not cables. So long as these are each cables, there is no prohibition with running them through a common raceway or opening. The cables don't even have to have the same insulation rating. No different than running NM and thermostat wire through the same hole.

                -Hal

                Comment


                  #9
                  Yes, they're multiconductor cables not conductors. I really appreciate the feedback!
                  Isaiah

                  Comment


                    #10
                    Originally posted by LarryFine View Post

                    The OP's situation would not have the differing voltages occupying the same cable.

                    That rule is about conductors sharing a conduit or a cable, not cables sharing a conduit.

                    The big question is whether conductors = cables. I say not.

                    Woops I thought the 1900V was sharing a cable with the other conductors,
                    Originally posted by Isaiah View Post
                    I have a vendor device that has ONE conduit hub for the following circuits: 120VAC power, 24VDC discreet signal (customer supplied cable) and 1900VDC (vendor supplied cable) ...
                    So is the 24V and 120V is sharing a cable then? Or is it two cables, a 24V and a 1900V being pulled in along side 120V THHN conductors?
                    Comments based on 2017 NEC unless otherwise noted.

                    Comment


                      #11
                      Originally posted by tortuga View Post
                      So is the 24V and 120V is sharing a cable then? Or is it two cables, a 24V and a 1900V being pulled in along side 120V THHN conductors?
                      Three separate cables, or at least two; the 120v might be individual conductors.
                      Master Electrician
                      Electrical Contractor
                      Richmond, VA

                      Comment

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