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Commercial solar PV grounding with CT cabinet supply side connection

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    Commercial solar PV grounding with CT cabinet supply side connection

    I am designing a 186kW PV system and need to make the grid connection on the supply side, and am using a CT cabinet. I would like some advice on grounding. The existing 480V service has an 800A fused main disconnect before the MLO panelboard. The Neutral and ground bond is in the main disconnect, as is the GEC. I have an AC combiner taking the three 62kW inverter outputs and providing a single PV System output to a 400A nonfused disconnect to serve as the PV System disconnect. I am bringing the system gound from the inverters thru to the ground bus in the combiner, and then then on to ground lug in System disconnect, and to the building main disconnect ground / neutral bus. I am unsure if the CT cabinet needs a separate ground or if just bonding the neutral to the ground in the CT Cabinet is what is required. I see example utility connection diagrams with the Netral bonded to the ground lug in the CT cabinet. Attached is the diagram. Is there anything wrong I am doing here? Explanations and/or code references would be appreciated.

    solarken
    Attached Files
    Last edited by solarken; 09-26-19, 11:13 PM.

    #2
    I don't think that there is anything glaringly 'wrong', but don't make any assumptions about what the AHJ's opinion is or should be. This is more or less another thread on whether 'the PV disconnect a service disconnect or not', which if you search through past threads you will find has been an intractable discussion here. The NEC has been quite vague on this stuff, although I believe the 2020 NEC will generally require and endorse what you've drawn, perhaps not to every last detail. The general alternative to what you've drawn would be to treat the PV disconnect as another service disconnect, and to have a main bonding jumper there and send an additional GEC from there to the existing grounding electrode system. In other words it would be mirror image of the existing service disconnect and you would not need a green wire running from one to the other. Either way, you have an effective ground fault path, either through the green wire in what you've drawn, or through the white wire if you do it the other way. You're AHJ, however, may think that for some reason it really matters which method you use.

    The only question/quibble I have with your drawing is that the ground symbol in the PV AC combiner should not represent an electrode. If that just represents the equipment ground terminal bar then it's fine.

    Comment


      #3
      As jaggedben wrote, some of this depends on how you treat the PV AC disconnect. Some AHJs require a system ground and some don't allow it. Outside of that the CT cabinet needs to be bonded to the rest of the grounded equipment with an EGC. The way it is drawn it is floating out there with no EGC. It will look like the EGC is duplicating the neutral connection to the building disconnect but there needs to be an EGC and a neutral even though they are technically in parallel.

      Comment


        #4
        Originally posted by jaggedben View Post
        I don't think that there is anything glaringly 'wrong', but don't make any assumptions about what the AHJ's opinion is or should be. This is more or less another thread on whether 'the PV disconnect a service disconnect or not', which if you search through past threads you will find has been an intractable discussion here.
        I wouldn't call it intractable; under present code it's compliant to do it either way. Ask the AHJ and do like they say.

        Comment


          #5
          Originally posted by pv_n00b View Post
          As jaggedben wrote, some of this depends on how you treat the PV AC disconnect. Some AHJs require a system ground and some don't allow it. Outside of that the CT cabinet needs to be bonded to the rest of the grounded equipment with an EGC. The way it is drawn it is floating out there with no EGC. It will look like the EGC is duplicating the neutral connection to the building disconnect but there needs to be an EGC and a neutral even though they are technically in parallel.
          I see the CT cabinet bonded to the neutral, as required for stuff on the supply side of the service disconnect. I also see an EGC or supply side bonding jumper brought from the service disconnect over to the PV disconnect. I think that's essentially okay, in context of other comments above.

          Comment


            #6
            Originally posted by jaggedben View Post

            I see the CT cabinet bonded to the neutral, as required for stuff on the supply side of the service disconnect. I also see an EGC or supply side bonding jumper brought from the service disconnect over to the PV disconnect. I think that's essentially okay, in context of other comments above.
            I just received the 2020 NEC version and was hoping it would provide some clarification on this, but not sure it does. I am now thinking I should remove the Neutral to Ground bonding jumper in the CT cabinet and run an EGC from the CT cabinet to the Main Disconnect that has the GEC and the main bonding jumper installed.

            Can you provide the NEC secionts that specify that the CT cabinet must have the neutral bonded to it's ground becuase it is on the supply side of the service disconnect? I provided the original dwgs to the AHJ and he is reviewing the permit application now, but have not yet received feedback from him on this.

            Thanks for the help.

            Comment


              #7
              Originally posted by pv_n00b View Post
              As jaggedben wrote, some of this depends on how you treat the PV AC disconnect. Some AHJs require a system ground and some don't allow it. Outside of that the CT cabinet needs to be bonded to the rest of the grounded equipment with an EGC. The way it is drawn it is floating out there with no EGC. It will look like the EGC is duplicating the neutral connection to the building disconnect but there needs to be an EGC and a neutral even though they are technically in parallel.
              I am tending to agree with you now, I think I need to remove the bonding jumper in the CT cabinet and run an EGC from CT cabinet to the building disconnect.

              Comment


                #8
                I didn't say those things, and I don't think you should do that if it represents the existing installation. The code section that supports bonding the CT cabinet to the neutral is 250.92.

                I just got my 2020 NEC the other day as well, and they removed the proposed section on bonding and grounding that would have clarified this stuff.

                Comment


                  #9
                  Originally posted by jaggedben View Post
                  I didn't say those things, and I don't think you should do that if it represents the existing installation. The code section that supports bonding the CT cabinet to the neutral is 250.92.

                  I just got my 2020 NEC the other day as well, and they removed the proposed section on bonding and grounding that would have clarified this stuff.
                  Can you clarify what you mean by "I don't think you should do that if it represents the existing installation"?

                  Comment


                    #10
                    I mean that if that bond already exists, I wouldn't remove it. If the CT cabinet isn't properly bonded now, there might be a more convenient way to bond it with a supply side jumper from somewhere else, or maybe bonding to the neutral in the cabinet would still be the best way.
                    Last edited by jaggedben; 10-08-19, 10:38 PM.

                    Comment


                      #11
                      Deleted
                      Last edited by jaggedben; 10-08-19, 10:39 PM. Reason: Accidental reply instead of edit.

                      Comment


                        #12
                        Originally posted by jaggedben View Post
                        I mean that if that bond already exists, I wouldn't remove it. If the CT cabinet isn't properly bonded now, there might be a more convenient way to bond it with a supply side jumper from somewhere else, or maybe bonding to the neutral in the cabinet would still be the best way.
                        I'm sorry, I might not have been clear. I am adding the CT Cabinet, it does not exist currently. The current service comes in from the utility transformer into the main building 800A fused disconnect. The load side of the disconnect goes to the panelboard main lugs. I am inserting a new CT cabinet between the utility transformer and the existing main 800A disconnect, to provide the extra lugs I need to land the solar on the supply side, and also to provide a convenient place to measure the current and voltage for the grid energy meter. As I add the CT cabinet, one of my questions was should I bond the neutral to the CT cabinet? There is already a Neutral to Equipment Ground main bonding jumper in the existing Main Disconnect.
                        Last edited by solarken; Yesterday, 10:01 PM.

                        Comment


                          #13
                          Originally posted by solarken View Post

                          I'm sorry, I might not have been clear. I am adding the CT Cabinet, it does not exist currently. The current service comes in from the utility transformer into the main building 800A fused disconnect. The load side of the disconnect goes to the panelboard main lugs. I am inserting a new CT cabinet between the utility transformer and the existing main 800A disconnect, to provide the extra lugs I need to land the solar on the supply side, and also to provide a convenient place to measure the current and voltage for the grid energy meter. As I add the CT cabinet, one of my questions was should I bond the neutral to the CT cabinet? There is already a Neutral to Ground main bonding jumper in the existing Main Disconnect.
                          Yes. Bonding between the service point and the service disconnect is done with the grounded conductor. You also have the choice of bonding it by running a bonding jumper to hit the grounded conductor somewhere else, such as the service disconnect. Usually CT cabs have a convenient way to bond the neutral buss to the cabinet.
                          Ethan Brush - East West Electric. NY, WA. MA

                          "You can't generalize"

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