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PV Interconnection at the Secondary of the Existing Transformer

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    PV Interconnection at the Secondary of the Existing Transformer

    Hey guys,

    We are doing a project where the final interconnection of the PV system is at the secondary of the existing transformer at the site (that also supplies the building). We asked the POCO for their guidelines for this interconnection (either to penetrate the t/f from the side or to go underground, etc) because the transformer is owned by them, but they said "Ask your Electrician". We are in talks with the couple of people, but did anyone here do such interconnection previously? if so how did you go about it?

    Ps. This T/F is located just outside the building above ground and installed on a PAD (Check attached)

    #2
    Where is the POCO's revenue meter? Most POCOs will not allow you to connect outside the meter.

    Comment


      #3
      Originally posted by ggunn View Post
      Where is the POCO's revenue meter? Most POCOs will not allow you to connect outside the meter.
      And if you are ever exporting power to the grid, you do not want that to be unmetered!
      Some jurisdictions meter the PV generation separately instead of offering net metering though.

      Comment


        #4
        Originally posted by ggunn View Post
        Where is the POCO's revenue meter? Most POCOs will not allow you to connect outside the meter.
        I am sorry I didn't mention - it is a 100% export to the utility and circuit is basically PV -> Inverter -> Switchboard -> Meter -> Interconnection point. So it is metered.

        Comment


          #5
          Originally posted by GoldDigger View Post

          And if you are ever exporting power to the grid, you do not want that to be unmetered!
          Some jurisdictions meter the PV generation separately instead of offering net metering though.
          Yes it is metered separately and exported 100% to the utility. It is a Community Solar

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            #6
            Just come up from underground like the existing service conductors. I can't imagine any POCO allowing anything else.

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              #7
              Originally posted by texie View Post
              Just come up from underground like the existing service conductors. I can't imagine any POCO allowing anything else.
              Thank you, is there any NEC code that we have to comply while doing such Interconnection?

              Also, since the transformer is already installed won't that be a task to trench into it? Or I am thinking to remove that transformer, then trench it, install conduits, pull the wire and then connect back the transformer. Wonder how much this is going to cost considering we have to provide a backup generator until we do this work!
              Last edited by TheElectrician; 11-07-19, 05:02 PM.

              Comment


                #8
                Originally posted by TheElectrician View Post

                Thank you, is there any NEC code that we have to comply while doing such Interconnection?

                Also, since the transformer is already installed won't that be a task to trench into it? Or I am thinking to remove that transformer, then trench it, install conduits, pull the wire and then connect back the transformer. Wonder how much this is going to cost considering we have to provide a backup generator until we do this work!
                Get a locate on the existing conduits, core a hole thru the slab, dig under to meet the new hole. Get everything set up and I bet its just a 1-2 hour outage.
                Ethan Brush - East West Electric. NY, WA. MA

                "You can't generalize"

                Comment


                  #9
                  Originally posted by TheElectrician View Post

                  Thank you, is there any NEC code that we have to comply while doing such Interconnection?

                  Also, since the transformer is already installed won't that be a task to trench into it? Or I am thinking to remove that transformer, then trench it, install conduits, pull the wire and then connect back the transformer. Wonder how much this is going to cost considering we have to provide a backup generator until we do this work!
                  You will need to work with the POCO as some, depending on the size and POCO standards, are sitting on a vault or just a concrete pad with a rectangular hole. Normally there is no need to remove the xformer. Not a big deal to do but details are important.

                  Comment


                    #10
                    Originally posted by electrofelon View Post

                    Get a locate on the existing conduits, core a hole thru the slab, dig under to meet the new hole. Get everything set up and I bet its just a 1-2 hour outage.
                    This is what I am thinking too, let me talk to the electrical contractors.

                    Comment


                      #11
                      Originally posted by texie View Post

                      You will need to work with the POCO as some, depending on the size and POCO standards, are sitting on a vault or just a concrete pad with a rectangular hole. Normally there is no need to remove the xformer. Not a big deal to do but details are important.
                      This T/F is sitting on a concrete pad with a rectangular cut out like in the pictures. We don't want to remove the transformer as well. I guess I will talk with my electrical contractors and do something like what electrofelon suggested.

                      Comment


                        #12
                        Originally posted by TheElectrician View Post

                        Thank you, is there any NEC code that we have to comply while doing such Interconnection?
                        The conductors between the utility-owned transformer and the Point of Common Coupling (PCC) are usually utility-owned. You might have to install them to the utility's specs but then they usually take ownership. The NEC provides some basic guidance for these conductors in NEC 230 Part III. From the PCC to the service disconnect the conductors are Service Entrance Conductors under NEC 230 Part IV.

                        Comment


                          #13
                          Originally posted by pv_n00b View Post

                          The conductors between the utility-owned transformer and the Point of Common Coupling (PCC) are usually utility-owned. You might have to install them to the utility's specs but then they usually take ownership. The NEC provides some basic guidance for these conductors in NEC 230 Part III. From the PCC to the service disconnect the conductors are Service Entrance Conductors under NEC 230 Part IV.
                          Got it, Thank you very much!

                          Comment


                            #14
                            The point of delivery (common coupling) is the secondary side of the XF.
                            On our system they will always be your wires, we never take ownership of your equipment.
                            metering here is easy. Slip on CTs over the spades, done...
                            the pad is a spec pad probably. Ours have a 4’X18” opening.
                            electricians dig under ours with no problem. We open the XF door while they are working to get in their conduits. If the XF is in service now you will have to come up with a safe plan to pull your conductors in.
                            I have rubbered up the spades and connectors for electricians many times for pulls.
                            I wouldn’t imagine the POCO would just open and leave...

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