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    Main service panel with feedthrough lugs and 120% rule

    Hello folks, this is my first post. Been reading the forum for some time, some great information.

    Im in the planning stage of a microinverter based system (Silfab 310 modules, enphase 7+ microinverters, and Ironridge racking).

    Im having some kinks in my planning due to a somewhat unusual main service panel with feedthrough lugs. Seems the NEC code is a little vague for this setup.

    I have a 200A main combination panel with feedthru lugs that feeds a 200A main breaker subpanel in my garage. The service panel basically feeds through to the panel in the garage that feeds all the primary house loads.

    I'd like to add a 60A PV system and would like to leverage the 120% rule if at all possible so that I only have to downsize to 175A main breaker to allow for future expansion.

    The main service entrance panel has a 50A breaker to an outlet for a compresser/portable equipment as the only load but I am considering future addition of 100A breaker to the main panel to feed an ADU.

    After reading the forum I found several old posts that seemed to offer conflicting information on how to consider the feedthrough lugs and attached panel for purposes of NEC 705.12 (b) (3)

    1) Some of the posts suggested that by placing the backfeed inverter into the panel furthest from the main breaker would meet (b) 120% rule. However the feedthrough lugs are at the end of the busbar, while not a physical breaker seems to violate the spirit of the code.

    2) Some other posts suggested that the (c) sum of breakers in subpanel might apply and the lugs are not considered a breaker in this panel for purposes of the calculation. The argument being that the feed lugs are characterized separately by the panel manufacturer and technically not part of the bus.

    3) The other option I was thinking of is to backfeed the solar into the furthest slot away from the main breaker of the subpanel in the garage and derate the service panel and subpanel breakers to 175A. For this scenario the 120% rule (b) would work for the subpanel in the garage but then when I carry this upstream to the main panel I would then possibly face challenge as there are not really any load breakers other than the 50A compressor in the main panel. It seems to expose the possibility the inspector might say that (b) implies that there are breakers present to spread out the loading which was the basis for the 120% rule. If I did add more breakers in the future then there would be some spreading of the current but it seems it comes to luck of the draw with the inspectors.

    Also for scenario 3, since I would no longer have the PV feeback breaker in the main panel, I would not have a solar disconnect within 10' of the main panel. The AHJ seemed ok with only having the A/C disconnect in the garage, but Im afraid PGE might make me have the A/C shutoff within 10' of the meter. If I wanted to install an AC shutoff, then it seems PGE wants it within 10' of the main panel. This would require looped the PV through an AC shutoff placed near the main and then back to feed the subpanel in the garage. This does not seem elegant and the extra detouring might present challenges meeting voltage rise.

    PGE has a document that shows scenario for when A/C shutoff is needed online, and my system seems to meet the criteria (no line side tap, no 3 phase, < 320A) but Im not sure if they are assuming central inverter based system, or might insist that I have it despite the "AC Disconnect and Variance Logic Standard NEM" document that says its not needed.

    Im thinking I might need to bite the bullet and downgrade my system to 50A and downside main breaker to 150A but this does not leave any room for future expansion.

    I would greatly appreciate any help in navigating my possible options and feedback on what you folks would do in my situation.

    Thanks,

    Kuma




    #2
    Option 3 is the simplest. It's totally compliant, and you are being too paranoid about it. For a service with a non-CT meter rated 320A or less PG&E do not require a disconnect. Also your theory that "(b) implies that there are breakers present to spread out the loading" is not correct as far as I understand. I believe that the idea is simply that the busbar distance between the two sources allows better heat dissipation regardless of what any loads are doing. And to my understanding that's not based on any real science either. So it really just comes down to following the letter of the code, which you would be doing in both panels.

    I agree that the following approaches would be exploiting 'loopholes' in the code and not meeting the safety standard that the rules intend:
    - not counting the feed through lugs as the 'opposite end' for the '(b)' 120% option
    - not counting the downstream 200A breaker in the subpanel as a load on the busbar for the '(c)' sum of breakers option

    Thus I don't see a defensible ability to use 'c' to avoid downsizing the main breaker.
    (In either case it would be worse, safety wise, if the subpanel did not have a main breaker, as you could theoretically feed 260A to the 200A subpanel.)

    The 2020 NEC will actually have a rule addressing feed through lugs. I just read it for the first time. I think it closes the loopholes mentioned above, and perhaps goes even more stringent.

    Comment


      #3
      Thanks for the feedback it is much appreciated.

      Back feeding the solar through the garage panel and no AC shutoff seems like the option that is the cleanest if PGE would be ok. The panel is centrally located towards the center of the house/panels and saves the main conduit run. I can just pop out the roof to the array directly above the garage panel to a string combiner box. It is where I would place the combiner box if I was backfeeding the main service panel. If Im using loads in the house (A/C) and generating solar it is less voltage drop for the loads.

      For my wife/kids If they needed to shut PV off for some reason, the garage panel is indoor type and easier to open/access than outside at the front of the house. It also seems more intuitive since all the load breakers are there and this is where they already know to go to reset breakers.

      When I spoke to the AHJ they thought PGE would insist I have the A/C shutoff if there was not a "PV" breaker in the main panel or other location reachable without breaking into the garage.
      Agreed with microinverters the system shuts down immediately if you kill the main breaker at the service entrance so I don't believe with proper labeling it is a real safety issue but Im interested to follow best practices if possible.

      My roof is all hip type and very easy access to the ridge for fire/ventilation on multiple sides so I expect it would be easy for first responders to stay clear of the PV. Im mostly concerned with getting PGE to pass it. The online "AC Disconnect and Variance Logic Standard NEM" document clearly shows AC Disconnect/Variance not required. Im wondering if anybody has had any experience with NorCal PGE for a similar setup?






      Comment


        #4
        I've done hundreds of these in PG&E territory. It's what I do every day. Here is when you don't need a PG&E disconnect. 99.9% of residential qualifies.

        Exemption to the Disconnect Switch installation Requirement
        Applicants with inverter-based generating systems that are supplied by PG&E single phase services up to 240 volts
        may be exempted from installing a disconnect switch, as determined by PG&E, if the meter panel that is
        interconnected with the generation source(s) meets all of the following conditions:
        • Self-contained (not transformer-rated).
        • Accepts form ”S” socket-based (e.g., FM2S) meters (not bolt-on meters).
        • Rated for 320 amps (CL 320) or less of “continuous” current.
        • Single-phase, 120/240 volt or 120/208 volt.
        Any generation system that does not meet these conditions must install a disconnect switch, as required by PG&E.

        Comment


          #5
          Option #1, I agree totally. 200 at main and 60 at PV wherever it is still totals more than 240
          Option #2, not really understanding how that works... potential is still there for more than 240 amps to flow over the main panel busbar.
          Option #3 Seems a little confusing, but may work.


          At our utility we allow our customers to connect on the source side of the main, generally with double lugs in the 320A meterbase.
          is this an option with PG&E??


          Also for #3, what’s to stop you when the inspector leaves?
          the rule is a good rule and was made for your exact predicament.

          Say you have a 200 amp main, and the total amperage ratings of all load breakers is >400A. That’s not unheard of and quite common... mine is over 550 amps in my house.
          should any combination of these pull more than 200 amps, the breaker will trip (based on its trip curve)
          No matter where you put the 60 amp breaker, whether it be at the main panel, sub panel, or any sub panel fed from the main panel, there exists the possibility that loads in the main panel could be over 200 amps, and the PV COULD supply the extra amperage to feed these loads.

          I know it’s about an impossibility, and realistically if your loads exceed the 200 amp main panels limit with the PV breaker connected at the BOTTOM of the panel, the PV theoretically should feed these loads, therefore resulting in no loads on your panel being over 200 (or 240)amps at any spot on the bus.
          Should the loads continue to increase and get over the 260A mark, (again, depending on breaker TCC), one or both breakers should trip. Without having the main bus ever seeing any loads over 200(240) amps.

          Its almost like your bus is separated.

          Comment


            #6
            Originally posted by jaggedben View Post

            The 2020 NEC will actually have a rule addressing feed through lugs. I just read it for the first time. I think it closes the loopholes mentioned above, and perhaps goes even more stringent.

            Are you sure about this. The 2020 will not allow the 6 handle rule in one enclosure but if there is a main breaker then you can have feed thru lugs. You may have meant this but I want to be clear with others about it. If I am wrong please tell me.
            They say I shot a man named Gray and took his wife to Italy
            She inherited a million bucks and when she died it came to me
            I can't help it if I'm lucky

            Comment


              #7
              Originally posted by Dennis Alwon View Post


              Are you sure about this. The 2020 will not allow the 6 handle rule in one enclosure but if there is a main breaker then you can have feed thru lugs. You may have meant this but I want to be clear with others about it. If I am wrong please tell me.
              The change to the six-handle rule affects this other recent thread more than it affects this one. In 2020 Article 705 will have new, separate references to both feed through lugs and to Article 230 with respect to supply side connections (705.12(A)). I have to say that from what I recall, the changes to 705 were not coordinated with the changes that you refer to that affect the 6 handle rule in article 230. In particular, I fear that adding solar connections to existing panels that were compliant under the old six-handle rules will become a thorny issue.

              Comment


                #8
                Originally posted by Hv&Lv View Post
                ...

                At our utility we allow our customers to connect on the source side of the main, generally with double lugs in the 320A meterbase.
                is this an option with PG&E??

                ...
                PG&E would allow it, but I find that this option generally isn't available for existing meter/main combo service panels. Unless the house truly needs 200A and can't live with 175A - and I've yet to do a load calculation on a single-family home where it came out that way - then downsizing the main to 175A is the cheaper, simpler option, on materials, labor, and bureaucracy.

                Comment


                  #9
                  Originally posted by jaggedben View Post

                  The change to the six-handle rule affects this other recent thread more than it affects this one. In 2020 Article 705 will have new, separate references to both feed through lugs and to Article 230 with respect to supply side connections (705.12(A)). I have to say that from what I recall, the changes to 705 were not coordinated with the changes that you refer to that affect the 6 handle rule in article 230. In particular, I fear that adding solar connections to existing panels that were compliant under the old six-handle rules will become a thorny issue.
                  Adding solar to an MLO panel that already has six handles does not violate the six handle rule (it's not a seventh handle to the same power source). Our benefactor has a lot to say on the subject and he helped me convince my local AHJ of it.

                  Comment


                    #10
                    Originally posted by ggunn View Post

                    Adding solar to an MLO panel that already has six handles does not violate the six handle rule (it's not a seventh handle to the same power source). Our benefactor has a lot to say on the subject and he helped me convince my local AHJ of it.
                    But you're not on the 2020 code yet. The 2020 NEC will prohibit the six disconnects from being in the same enclosure. So what will your AHJ say when you have an existing MLO service panel with however many handles and you want to add one more? Will they grandfather the whole service enclosure or not?

                    for me this problem is 3+ years away but I'm still not looking forward to the uncertainty.

                    Comment


                      #11
                      Originally posted by jaggedben View Post
                      I've done hundreds of these in PG&E territory. It's what I do every day. Here is when you don't need a PG&E disconnect. 99.9% of residential qualifies.
                      Jaggedben, greatly appreciate the help. Im new to dealing with PGE and Im trying to plan carefully to avoid problems that might require looping back to the city.
                      I thought about line side tap, had many benefits especially if I add an ADU, but with the variances involved it seemed like a complicated route for me.
                      Think downsizing the breakers to 175a and feeding into the garage panel for now is the way to go.

                      I had tried contacting PGE solar department for clarification on a few points but the phone reps were clearly non technical and couldn't get me in touch with somebody who was. According to them before I can file an application or talk with them I need to already have the solar installed and permit signed off by AHJ.

                      Im kind of disappointed I had opted for the 8/16 feed through service entrance panel when I upgraded to 200A a little while back.
                      The feedthrough lug panel seemed a cleaner approach to feed the garage subpanel as it eliminated a redundant breaker.

                      Had I planned for solar I could have opted for the sibling 2040 panel and a 200A load breaker to feed the subpanel in the garage. Its the exact same box, just longer busbar. This would have allowed me to backfeed at the main service panel and put the sources at opposite end of bus and still apply the 120% rule.

                      Problem with feed thru lugs panel is there is no easy way to leverage the 120% rule. If I compare specs between the 816 and 2040 panels, the 816 has a smaller max amps/bus stab that seems to be extra padding to account for the extra current feeding through the busbar/lugs. With the small number of slots and limited current/stab I think it would be hard to configure it in a way it would overheat with only 20% extra current.

                      The 120% rule involves a bit of excess pessimism removal. The center fed panel got lucky in the last NEC round, but still no help for the feed through lug panel owners.
                      Glad I think I have a way to work around for now.

                      Thanks much,

                      Kuma

                      Comment


                        #12
                        Originally posted by jaggedben View Post

                        But you're not on the 2020 code yet. The 2020 NEC will prohibit the six disconnects from being in the same enclosure. So what will your AHJ say when you have an existing MLO service panel with however many handles and you want to add one more? Will they grandfather the whole service enclosure or not?

                        for me this problem is 3+ years away but I'm still not looking forward to the uncertainty.
                        Actually, when we did it the AHJ had us mount a fused disco on the wall next to the panel and tap the bus. Electrically it was no different (it was still a "seventh handle") but it was no big deal.

                        Comment


                          #13
                          Originally posted by Paul Donehue View Post

                          Jaggedben, greatly appreciate the help. Im new to dealing with PGE and Im trying to plan carefully to avoid problems that might require looping back to the city.
                          I thought about line side tap, had many benefits especially if I add an ADU, but with the variances involved it seemed like a complicated route for me.
                          Think downsizing the breakers to 175a and feeding into the garage panel for now is the way to go.

                          I had tried contacting PGE solar department for clarification on a few points but the phone reps were clearly non technical and couldn't get me in touch with somebody who was. According to them before I can file an application or talk with them I need to already have the solar installed and permit signed off by AHJ.

                          Im kind of disappointed I had opted for the 8/16 feed through service entrance panel when I upgraded to 200A a little while back.
                          The feedthrough lug panel seemed a cleaner approach to feed the garage subpanel as it eliminated a redundant breaker.

                          Had I planned for solar I could have opted for the sibling 2040 panel and a 200A load breaker to feed the subpanel in the garage. Its the exact same box, just longer busbar. This would have allowed me to backfeed at the main service panel and put the sources at opposite end of bus and still apply the 120% rule.

                          Problem with feed thru lugs panel is there is no easy way to leverage the 120% rule. If I compare specs between the 816 and 2040 panels, the 816 has a smaller max amps/bus stab that seems to be extra padding to account for the extra current feeding through the busbar/lugs. With the small number of slots and limited current/stab I think it would be hard to configure it in a way it would overheat with only 20% extra current.

                          The 120% rule involves a bit of excess pessimism removal. The center fed panel got lucky in the last NEC round, but still no help for the feed through lug panel owners.
                          Glad I think I have a way to work around for now.

                          Thanks much,

                          Kuma
                          One potential problem with feedthrough lugs is that you have to think about what is being fed by them. If it's an MLO subpanel then you could be overloading it.

                          Comment


                            #14
                            My setup has a main breaker panel. If I put my solar feed at the end of the box (by the feed lugs) and my 50A single load breaker, think there is no way it would overheat the bus. Just does not meet the code as currently written.

                            Comment


                              #15
                              Originally posted by Paul Donehue View Post
                              My setup has a main breaker panel. If I put my solar feed at the end of the box (by the feed lugs) and my 50A single load breaker, think there is no way it would overheat the bus. Just does not meet the code as currently written.
                              That's kind of a gray area. More significant is what is on the other end of the conductors connected to the feedthrough lugs.

                              Comment

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