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    Voltage issue

    Bottom line is that I messed up on a design. I designed two new 480/277V, 3ph, 4W panels to two seperate existing 480V, 3ph, 3w distribution panels. See attached one line diagram for reference. What would be the best way to correct this mistake? The 480/277V, 3 ph, 4W panels are already installed and the feeders have been pulled. The electrical contractor just brought this to my attention. Thank you.
    Last edited by john2016; 10-21-19, 09:47 PM.

    #2
    Originally posted by john2016 View Post
    Bottom line is that I messed up on a design. I designed two new 480/277V, 3ph, 4W panels to two seperate existing 480V, 3ph, 3w distribution panels. See attached one line diagram for reference. What would be the best way to correct this mistake? The 480/277V, 3 ph, 4W panels are already installed and the feeders have been pulled. The electrical contractor just brought this to my attention. Thank you.
    The panel labeling probably says it must be installed on a system that does not exceed 277V L-G. It likely does not require that a neutral conductor actually be run to panel.
    Just because you can, doesn't mean you should.

    Comment


      #3
      Do panels 1ERCH1 and 1ERSH1 have any line-to-neutral loads? If so, the only solution I see are 480-480Y/277 transformers.
      The more they overthink the plumbing, the easier it is to stop up the drain

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        #4
        One of the panel has lighting loads at 277V. I was thinking 480-480Y/277 transformers as well but wanted to see if anyone had any other ideas. Thanks.

        Comment


          #5
          Is the problem that there is no neutral? Can one be added?
          Master Electrician
          Electrical Contractor
          Richmond, VA

          Comment


            #6
            Originally posted by dkidd View Post
            Do panels 1ERCH1 and 1ERSH1 have any line-to-neutral loads? If so, the only solution I see are 480-480Y/277 transformers.
            What is going to cost more, installing the transformer(s) or pulling a neutral?
            I live for today, I'm just a day behind.

            Comment


              #7
              Originally posted by LarryFine View Post
              Is the problem that there is no neutral? Can one be added?
              Might be harder than we think. There is a neutral from the utility to the MDP. We don't know if it was also carried to MDPA. But both of them are 3W, so I don't know where the neutral would be landed. If the neutral is available at the two MDPs, you would have to bring it through the ATSs and to the downstream panels EDP and ECDP (which are also 3W), and from there to the new panels.

              But I see a far more significant issue. Gen 1 is called a "Separately Derived System," and Gen 2 is called a "Non-Separately Derived System." Someone please check me on this. I don't believe that can happen (i.e., one of each type) at the same facility. An SDS would require the generator's neutral to be bonded to its case, and would require downstream ATSs to switch the neutral (i.e., 4 pole). The Non-SDS would require the generator's neutral to not be bonded to its case, and would require downstream ATSs not to switch the neutral (i.e. 3 pole). The PDF does not show us the complete wiring downstream of the two generators, and it does not say whether the ATSs are 3-pole or 4-pole. So I can't tell if this system was set up correctly.

              Charles E. Beck, P.E., Seattle
              Comments based on 2017 NEC unless otherwise noted.

              Comment


                #8
                Unfortunately there is no neutral between the two MDP's. Hopefully you can read the one line diagram below. I couldn't get the PDF to attached since it was over 2MB.
                Last edited by john2016; 10-21-19, 09:35 PM.

                Comment


                  #9
                  Another issue may be its a corner grounded delta service instead of a wye, so there would be no 277 tap, so a 480 to 480/277 volt transformer may be the only solution.

                  Comment


                    #10
                    Originally posted by john2016 View Post
                    One of the panel has lighting loads at 277V. I was thinking 480-480Y/277 transformers as well but wanted to see if anyone had any other ideas. Thanks.
                    Might be cheaper to replace the lights.
                    Bob

                    Comment


                      #11
                      Originally posted by john2016 View Post
                      Unfortunately there is no neutral between the two MDP's. Hopefully you can read the one line diagram below. I couldn't get the PDF to attached since it was over 2MB.
                      Sent you a PM

                      Depending on the load there is hope- I'd imagine the lights and other items typically on 277 are on 120.

                      Comment


                        #12
                        Originally posted by charlie b View Post
                        Might be harder than we think. There is a neutral from the utility to the MDP. We don't know if it was also carried to MDPA. But both of them are 3W, so I don't know where the neutral would be landed. If the neutral is available at the two MDPs, you would have to bring it through the ATSs and to the downstream panels EDP and ECDP (which are also 3W), and from there to the new panels.

                        But I see a far more significant issue. Gen 1 is called a "Separately Derived System," and Gen 2 is called a "Non-Separately Derived System." Someone please check me on this. I don't believe that can happen (i.e., one of each type) at the same facility. An SDS would require the generator's neutral to be bonded to its case, and would require downstream ATSs to switch the neutral (i.e., 4 pole). The Non-SDS would require the generator's neutral to not be bonded to its case, and would require downstream ATSs not to switch the neutral (i.e. 3 pole). The PDF does not show us the complete wiring downstream of the two generators, and it does not say whether the ATSs are 3-pole or 4-pole. So I can't tell if this system was set up correctly.
                        In addition, with just a brief glance at the drawing I don't see how you can have a non-SDS genset connected to 3 wire gear.

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