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    NEC 2014 Grounding Question

    Hello,
    I was wondering if you could help me out with my question in red in the attached pdf. The question is in part 2. Sorry about the 2 pdf's; it is because of the size limitation. Thank you!
    Attached Files

    #2
    Sounds like you're asking about how to calculate the SBJ when you have parallel secondary conductors. It's fairly straight forward you just add up the CM size of total number of ungrounded conductors per phase. So if you had 3 sets of parallel 250 kcmil your calculation would be 3*250 kcmil= 750 kcmil, this is your equivalent conductor size. You would then go to the table and find the SBJ size for a 750 kcmil conductor. They made it more complicated by using a conductor size (#3/0) that is not in circular mils.
    Rob

    Moderator

    All responses based on the 2017 NEC unless otherwise noted

    Comment


      #3
      I was trying to say that in the example they are saying that the SBJ is the one between X0 and the XFMR’s neutral bar, vs. the picture shows the SBJ as the one between the XFMR’s neutral bar and its enclosure.

      Comment


        #4
        The conductor that is highlighted in yellow is the neutral.
        Rob

        Moderator

        All responses based on the 2017 NEC unless otherwise noted

        Comment


          #5
          Is this the section in question?

          In this case, however, the system bonding jumper is installed at the transformer and connects the transformer neutral terminal (X0) to individual supply side bonding jumpers that are installed between the panelboard EC terminals and a terminal bus attached to the transformer enclosure.
          Rob

          Moderator

          All responses based on the 2017 NEC unless otherwise noted

          Comment


            #6
            Yes, my problem is with that statement. It says that the SBJ connects the X0 with SSBJ's, while on the picture the SBJ is that piece between the XFMR neutral bar and the XFMR enclosure.

            Comment


              #7
              I agree the wording in post #5 does not match the graphic that you've posted. The graphic does not have "a terminal bus attached to the transformer enclosure" it has a neutral bus and an SBJ connected to the enclosure.
              Rob

              Moderator

              All responses based on the 2017 NEC unless otherwise noted

              Comment


                #8
                Thank you! I understand now that there are many scenarios of system bonding jumper setups. The terminal bus attached to the XFMR enclosure (the scenario in the calculation example) serves as the connection point between the system bonding jumper and the grounding electrode conductor. This is a slightly different scenario than what Exhibit 250.14 shows, but it doesn't make either presentation wrong. Thanks again! Have a great day!

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