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New Solar Installation Tie-in to Main Panel

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  • New Solar Installation Tie-in to Main Panel

    Hi, first time poster and home owner (non- electrician) in the middle of installing a new 20KW grid tied system and am looking for some input. I will be meeting with my electrical contractor later this week and want to understand the proper options available for tieing into my main panel. My system involves 70 Solarworld 285w panels which I already installed on my garage roof along with Solaredge optimizers feeding into 2 10KW inverters. My meter along with a 200 amp disconnect is located near the road which is 400 ft from my house where my main 200 amp panel is located. The two inverters are located in my detached garage which is 70 ft away from my house main panel. I'm new to solar systems and could figure out the roof top panel installation ok but just want to understand the electrical tie in side of the installation so when discussing it with my electrical contractor I'm sure we are doing the tie in properly. I've been told by an electrician that I could tie into my main panel with a 100 amp breaker but I've read about the 120% rule and it appears that this would be permitted by the code. Obviously the AHJ will be reviewing the layout prior to installation. Any input would be greatly appreciated....thanks!!!

  • #2
    I meant to say that per the 120% rule the 100 amp breaker option appears that it would NOT be permitted. Sorry!


    • #3
      A 100A backfeed breaker would vertainly break the 120% rule. You are going to have to go with a line side tap. This can be done a number of ways. 1 is to use a special adapter that fits between the meter and the meter base. Another is to use insulation piercing connectors to tap into the service wires between the meter and main breaker. You could also use mechanical multitap connectors (Unitap or Polaris).


      • Truenorth
        Truenorth commented
        Editing a comment
        Thanks for the confirmation of my suspicions! I'm also going to check into the mechanical taps.

    • #4
      Also I think 2 se10000's require >=105a breaker

      You could probably get away with 2 se7600s or definitely 1 se10000 and 1 se7600.
      Last edited by sunnyguy; 11-03-2016, 01:22 PM.


      • Truenorth
        Truenorth commented
        Editing a comment
        I should have posted on the forum prior to purchasing the inverters since I already bought the 2 10000's. One quote did suggest one 10000 and one 7600 but others offered the two 10000's for same price. I am using 4 strings two at 18 panels and two at 17 panels so I can run two strings with 35 panels into each inverter equally. Thanks!

    • #5
      Thanks for the feed back, I will review these options!


      • #6
        If there's a 200A breaker at the meter and a 200A breaker at the panel at the house, the AHJ might allow the wires between them to be tapped and connected to a backfeed breaker of 100A (possibly even up to 200A)
        It wouldn't be a line side tap because it would be after the first 200A breaker.
        And it would be safe because there could never be more than 200A in any section of that wire and the wire was sized for 200A.

        Another possibility is you can probably downsize the 200A main breaker at the house to 125A and have a backfeed of 100A at the opposite end of the breaker bar and that would use the 120% rule to meet code. That requires the electrician to do a calculation to make sure that 125A is sufficient for your house. (probably is - but depends on what all you have using electricity in your house - if you have a walk-in freezer, electrical baseboard heat, electric drier, electric hot water, electric kitchen, large AC units, etc - it is possible to be required to have more than 125A.

        And I agree with others that a pair of SE10k needs >100A breaker - probably winds up being 125A. Also if your main panel has a 200A breaker but a larger amperage bus bar you get 120% of the bus bar which might give you more room.

        Of course I am not an electrician - but since you will be talking to one, you will be able to rely on his advice and not mine.


        • Truenorth
          Truenorth commented
          Editing a comment
          I'm thinking your first suggestion is a good possibility. I probably can't downsize my 200A main due to so many amps load coming out of this main panel: 60A geothermal heat pump, dryer, kitchen stove, sauna stove etc and not to mention two 100A subpanels (one to garage and one feeding the house) coming out of this as well. I opened this main panel this morning and it looks like the busbar is only 200A and not 225A at least what I could read from UL label inside panel as it didn't specify it to be 225A. Thanks for input!!

      • #7
        The conventional solution to this situation is to replace your 200A main panel (at the road) with a 400A service - which is actually two 200A sections and use one of these 200A sections just for your solar backfeed. This will cost plenty of course.
        BSEE, R11, NABCEP, >1200kW installed


        • Truenorth
          Truenorth commented
          Editing a comment
          I've thought about this option too but as you mention this could be costly since I'm like 400ft from this location. I've also read about a 'ranch panel' (that's what it was called) being used which would have two 200A legs where you feed the house main panel from the ranch panel so it is a subpanel and then tie in the solar into the other leg. I haven't seen this just read about it. I think foo1bar solution is similar to this but probably less expensive. Thanks for feedback!!

      • #8
        Be aware of another potential problem. I read that you are feeding your inverter output back 470' to the PoCo. The inverters
        pushing 20KW back to the PoCo will cause a rise in voltage at the inverter end, due to voltage rise in the long runs. Here is a
        similar run, and 15KW combined with high line voltage caused my inverter output voltage to sometimes rise high enough to
        cause a high voltage shut down. At 20 KW this is even more likely. However a combination of moderate line voltage and
        heavy conductors to minimize voltage rise may solve the problem. I'd certainly make the 70' run of pretty heavy stuff. Bruce Roe


        • Truenorth
          Truenorth commented
          Editing a comment
          Excellent point and something I hadn't thought of. I will make sure my electrical contractor considers this. Thanks Bruce!!

          PS: One point I didn't mention in my first post is our area does not have an abundance of solar power so our AHJ's and contractors aren't doing this every day....that's why I'm reaching to the outside world to get some current opinions. Just want to do things correctly!

      • #9
        Most poco's do not like a line side tap between the meter and panel WITHOUT a breaker upstream. it is a liability thing as they are responsible for OCP until the first cb. Your solar has no business in your house panel, it needs a dedicated panel. 400a service is a joke and unless the poco demands it, it should not be considered. draw what I have shown below and submit it to the poco for your agreement. if they see a 200a cb immediately after the meter, they don't care any longer as the risk is yours not theirs...

        What you should do...
        Meter -> 200A CB outdoors at road/meter -> tap box near house panel -> separate wire feeds to 125/150a dedicated solar panel with seperate fused utility disconnect outdoors and 200a house panel wired straight to tap box

        consult poco on where they want the solar disconnect it's for them, not you.. if they want it at the meter 400' away it's gonna be expensive for all of that ac wiring. show it on the house in the drawings for your agreement. be crystal clear where the locations are with distances mentioned, when they approve it then change their mind when they realize it is 400' away you have them by the sack. I called my poco and they were quite helpful and honest.

        1. Buy a Midwest Electric terminal box (3r, ul rated, service rated metal 200A tap box for about $250, google it, pretty sweet!) a silly plastic box with Polaris taps is a joke and will break. self piercing taps are not ideal as you cannot inspect the connections. use a terminal box with lugs, or Polaris lug taps in that order... self piercing should be a last resort...not for new construction in my opinion. adding taps inside the old 200a panel to make the subpanel is not allowed due to space required some panels have an add on gutter for this but is a pita and silly.
        2. Buy a quality dedicated solar sub panel, must be backfeed only, no loads (maybe $250 loaded) I would do what is easy to source parts for...sq d qo series is my suggestion
        3. Add a digital plug in kwhr meter. analog only have 5 digits and you will max it out and roll it over in short order, digital has 6+ digits and cost the same. Add upstream of the subpanel.

        why the hell did you spend $30k on this system and not have a drawing and agreement with your poco prior to purchase? pretty risky...

        run the dc cabling the long distance, not the ac. I have over 450' of dc cabling from panels to inverters and didn't have to increase awg. check with SE about a length spec on the dc and also run the numbes on voltage drop as you will have to increase ac cable size after 100', but not dc. 10awg pv or se2 is cheap...just saying...

        pay attention to the ground bonding due to the 200a shutoff at the meter 400' away...this will get you in trouble if overlooked.

        "I've been told by an electrician that I could tie into my main panel with a 100 amp breaker" umm no! this is totally wrong and will be the insurance company's reason for not covering your house when it burns down. This guy hasn't read the code for a while...or ever and should be kept on a very short leash...does he have liability insurance? and a license? I wouldn't take his advice or work performed if the answer is no.

        your welcome
        Last edited by Eleceng1979; 11-08-2016, 11:33 PM.


        • Truenorth
          Truenorth commented
          Editing a comment
          Thanks for sharing some good input, I have met with a licensed electrical contractor (not the electrician providing offhand prelim input which agreeably was incorrect). I've shared all input received from the forum with him which I've told him is free input to ensure all bases are covered since 20kw installations aren't installed every day. He is also consulting with the AHJ to review the layout.

          As far as buying a system prior to having poco approval, I had a written agreement in place awhile ago and they provided their requirements which we are making sure are met.

          Thanks for the detailed suggestions!!

      • #10

        I am not an engineer but an electrical contractor. I have only done one solar install for a customer that installed his own system. The customer wired all his panels to the inverter left the line termination and permits for me. It was a small 5kw array which I did install on a qo 2 pole 30 amp breaker directly in his house panel. I'm curious as to why solar needs its own panel ahead of the main breaker. I have installed many generators and some times due to cost or astectics we are requested not to use a transfer switch and instead use a "generator interloc". In this installation I install a 2 pole breaker in the main panel and the interlock prevents to generator breaker and main breaker from being turned on simultaneously. As both a generator and a solar array generate power and backfeed it in to the panel bus I am curious what dangerous situation I might be creating. The. Reason I'm on this forum is I'm about to purchase and install my out grid tied system and I'm trying to glean as much knowledge from those in the know as possible. My plan was a simple install 5-6 kw SMA system as my garage has 0% chance of ever seeing any shade on it. However I planned to wire my inverter into my garage panel which is a 100 amp panel feed by #2 copper from a 100 amp breaker in the main panel in my house. All the generator and solar installs were inspected and approved by various local and state inspectors. So in a nut shell with as few 3 letter acronyms as possible why should something that generates power never go in the main house panel. The solar install that started this thread is the same size as the generators I install for customers so any input would be helpful. Thanks you in advance.



        • #11
          For openers your generator will never be feeding the panel at the same time as the PoCo; a grid tie will. The fear
          is if these 2 sources are at one end of the system, say 200A, the line source of 200A plus say a 60A inverter
          could feed 260A into a big load and damage the 200A busbars. This can be entirely avoided by placing the 2 sources at opposite ends of a feed system, so that nowhere in between can the currents add up in the busbars. That in fact is what is usually required for GTI; place the GTI breaker at the opposite end of the box from the
          PoCo feed breaker.

          In fact it may additionally required that the sum of the 2 feeding breakers not exceed 120% of the size line feed, so a
          200A line feed could have a 40A GTI breaker. The line breaker is sometimes reduced to allow a larger GTI breaker.
          Of course if the breakers are already at opposite ends, this gives belt and suspenders protection.

          My own experience is that GTI coming on with high power every day, and off at night, apparently by the heat/cool
          cycles tends to loosen up wire connectors. I have gotten into checking and tightening them a couple times a year
          to avoid burned up connections, but using much larger wire should reduce heating and help a lot. Bruce Roe
          Last edited by bcroe; 02-07-2017, 05:56 PM.


          • #12
            thank you serious food for thought. The power company in our area will email me a customers annual usage with the customers permission, with this I can see average usage as well as peak usage. I use this to size the generator and determine if load shedding switches are a good idea. In the case of my own pending install 125% of my peak and 125% of my solar is less than 200 amps so I will not be installing all the extra equipment eleceng recommended. Thanks again. I'm off the lurk some more and try to figure out string, optimizer or micro.