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Ground Wire Size for PV Array

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    Ground Wire Size for PV Array

    Looking for input regarding the grounding conductor from the inverter location to the roof top PV panels and racking on a typical grid-tied PV system. Since I don’t install PV systems, I don’t keep up with all the NEC requirements.

    We are just completing the rough wiring of a single-family dwelling. The homeowner has a contract with a local PV company to install the PV system once the home is complete. The PV company and homeowner have requested that we prewire for the future PV system. We do this all the time by running a 1” EMT raceway from the roof to the future inverter location.

    The way this home is designed with multiple roof levels it will be almost impossible to get between the array and inverter with EMT. The homeowner prefers not to see any exposed wiring on the roof.

    I just received info from the PV company that they want us to run (2) 10-4 MC cables for 2 strings since EMT is not practical. The also specified that we need to run a solid bare CU #8 with the MC cables. I sent a reply back questioning the solid bare #8. They state the #10 ground in the MC is not large enough to bond the rooftop equipment, it requires #8. They also state that solid wire is required if not in a raceway.

    I think they are definitely confused as far as the solid wire is concerned. 250 requires grounding/bonding wires smaller that #6 to be protected. It doesn’t have any different protection requirements for solid vs stranded.

    The sizing is something I need to investigate. I just received this request so have not reviewed the NEC yet but wanted to post here since I was on the forum now.

    From seeing systems installed most installers seem to be all over the place for the ground sizing. I see many systems installed with #10’s for the DC and #10 ground in EMT. I see other systems with #10’s for the DC and #8 or #6 ground in the EMT.

    I also question that if a larger ground is required, can it be run next to the MC cables. Generally the grounding conductor is required to be installed in the same raceway or cable sheath as the other conductors.
    Curt Swartz
    Electrical Contractor

    #2
    If this is actually in San Jose then you need the #8 because that's their way of enforcing 690.47(D). They don't actually make you install an additional electrode but they do require a 'GEC' from the array. Other jurisdictions in the area that I'm familiar with, except Palo Alto, mostly don't enforce that stupid requirement, which will go away at the end of the year.

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      #3
      Originally posted by jaggedben View Post
      If this is actually in San Jose then you need the #8 because that's their way of enforcing 690.47(D). They don't actually make you install an additional electrode but they do require a 'GEC' from the array. Other jurisdictions in the area that I'm familiar with, except Palo Alto, mostly don't enforce that stupid requirement, which will go away at the end of the year.
      Thanks for the reply. This is not in San Jose but a small single inspector city next to Los Gatos. I have no idea how this inspector is enforcing the grounding.

      Since my guys will need to do this work tomorrow I'll probably just have them run the additional ground. I can't think of any reason to run solid wire within the dwelling. Since the wire will not be installed in a raceway or cable I feel it needs to be at least #6. I'll probably just run a #6 green THWN from the inverter J-box to their roof deck box.
      Curt Swartz
      Electrical Contractor

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        #4
        Los Gatos or next to Los Gatos? Pretty sure Los Gatos wouldn't care.

        I would either run the #8 or get the inspector's assurance first that it's not required. The PV company is probably being conservative, or else they know his opinion. You wouldn't want to find out you're wrong after the walls are closed up.

        (I'm curious how they plan to bring the MC to the roof. Transition in attic boxes? Soladeck? We usually run flex so we can transition to EMT to go through the roof deck and pull wire before finishing.)

        Comment


          #5
          Monte Sereno.

          They want us to pull the MC's and ground leaving a long coil in the area of the roof box. They said they will have one of there installers stop by to install a SolaDeck box and land the cables prior to spray foam insulation of rafter bays.
          Curt Swartz
          Electrical Contractor

          Comment


            #6
            Originally posted by jaggedben View Post
            If this is actually in San Jose then you need the #8 because that's their way of enforcing 690.47(D). They don't actually make you install an additional electrode but they do require a 'GEC' from the array. Other jurisdictions in the area that I'm familiar with, except Palo Alto, mostly don't enforce that stupid requirement, which will go away at the end of the year.
            We have a couple of AHJ's who want the same thing, and we do a lot of work in their areas, so we just always run #8 to keep things simple.

            Comment


              #7
              Originally posted by jaggedben View Post
              If this is actually in San Jose then you need the #8 because that's their way of enforcing 690.47(D). They don't actually make you install an additional electrode but they do require a 'GEC' from the array. Other jurisdictions in the area that I'm familiar with, except Palo Alto, mostly don't enforce that stupid requirement, which will go away at the end of the year.
              We are pretty sure that stupid requirement caused this, there really isn’t any other explanation because the houses in that tract have ufers

              https://forums.mikeholt.com/forum/ac...v-installation

              the gas company supervisor that was killed, he replaced a good friend of mine a few years ago when my buddy was promoted to manager. I’ll see him this weekend and find out how the investigation is going,

              as far as the EGC, how it’s ran depends on if it’s central inverter/optimizer or if it’s micro inverters.

              If they want to “future proof” probably the best bet would be to run a 3/4” EMT from adjacent to the service to a roof stub and then another stub in 3/4” emt out the service to a different box adjacent to to the service. Either way, there is going to be some combination of equipment/switches adjacent the service panel and the DC cables can’t enter the main service

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