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    208 3ph to 230-240 Y transformer

    Wondering if it's OK to connect a 208 3ph 230-240Y 112kva transformer to a 3phase subpanel the input current is 100amps

    #2
    Originally posted by Bill 12 View Post
    Wondering if it's OK to connect a 208 3ph 230-240Y 112kva transformer to a 3phase subpanel the input current is 100amps



    Whats the 240Y for? Your source is 208 volts and the secondary is 240Y?

    Comment


      #3
      I'm curious, why that large of a transformer for a 100-amp circuit?

      If you have the proper OCP in place, I don't believe the NEC has a problem in under using a transformer's rating. I have heard that transformers might waste more energy when lightly loaded.

      Comment


        #4
        It will feed a 3ph sub panel that is powering a bunch of 240 3ph equipment one is a 100amp welder.

        https://www.larsonelectronics.com/p-...BoCQuwQAvD_BwE

        This is the transformer they want me to get. Sorry it a 75kva not 112 that was wrong

        Comment


          #5
          Originally posted by Bill 12 View Post
          It will feed a 3ph sub panel that is powering a bunch of 240 3ph equipment one is a 100amp welder.

          https://www.larsonelectronics.com/p-...BoCQuwQAvD_BwE

          This is the transformer they want me to get. Sorry it a 75kva not 112 that was wrong
          That transformer is single phase. You won't be able to power 240 3ph equipment with it.


          Maybe the wrong link?

          Comment


            #6
            Originally posted by Bill 12 View Post
            It will feed a 3ph sub panel that is powering a bunch of 240 3ph equipment one is a 100amp welder.

            https://www.larsonelectronics.com/p-...BoCQuwQAvD_BwE

            This is the transformer they want me to get. Sorry it a 75kva not 112 that was wrong
            So I'm guessing that this will be a 3Ø, 3wire, 240 volt system without a neutral? If you need to supply any 120 volt loads then a 3Ø,4W Delta secondary might be better. A 240 volt Wye system has a phase to neutral voltage of 139 volts.
            Last edited by infinity; 03-14-19, 04:09 PM. Reason: Spelling
            Rob

            Moderator

            All responses based on the 2017 NEC unless otherwise noted

            Comment


              #7
              Larson gave me 2 quotes here is the other one
              https://www.larsonelectronics.com/p-147482-.aspx

              Comment


                #8
                So we are trying to keep from running a new service which would entail changing a main panel to a 400amp and doing a hot tap and 200ft of new wire

                Comment


                  #9
                  Originally posted by Bill 12 View Post
                  Larson gave me 2 quotes here is the other one
                  https://www.larsonelectronics.com/p-147482-.aspx
                  112.5kva is the correct one.


                  Yes it can be done- make sure your sub panel has straight rated breakers only and no 120 volt loads.

                  Comment


                    #10
                    OK cool. So if they wanted 120 also could I get a transformer that would do that also?

                    Comment


                      #11
                      Originally posted by Bill 12 View Post
                      OK cool. So if they wanted 120 also could I get a transformer that would do that also?

                      You would use the 208 volt system for that.

                      Comment


                        #12
                        Originally posted by Bill 12 View Post
                        OK cool. So if they wanted 120 also could I get a transformer that would do that also?
                        Look at post #6.
                        Rob

                        Moderator

                        All responses based on the 2017 NEC unless otherwise noted

                        Comment


                          #13
                          Very confusing thread; let's try to clarify:

                          So you HAVE a 208V 3 phase system, right?

                          They WANT you to supply their equipment with 240V 3 phase, is that right?

                          If so, on that 240V system, do they need you to have 120V single phase as well?
                          __________________________________________________ ____________________________
                          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


                            #14
                            Originally posted by Bill 12 View Post
                            So we are trying to keep from running a new service which would entail changing a main panel to a 400amp and doing a hot tap and 200ft of new wire
                            Have you done a load calculation for the new equipment? Is there room in the existing service load calculation to accept the new loads?

                            And that 112 kVA transformer is overkill for a 100-amp sub panel.

                            Comment


                              #15
                              Yes there was. Well they ended up not using the transformer they ended up doing a new 400amp panel, disconnects 200ft of wire and $24,000

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