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  • A few questions about Grid-tie and SES specifics

    I am in Phoenix, AZ, USA and I am planning a solar self-install on my roof using Enphase microinverters with a grid tie installation of 6.2-6.6 KW.
    My utility (APS) requires that I install both a Solar meter and a disconnect. I'm trying to figure the specifics of my system and have a few questions.

    To start off, I want to say that I know it is ultimately up to the exact conditions of my home and the opinion of the AHJ whether or not something is acceptable and meets code. Also, when it comes to actually working on the Main SES, I will hire an electrician, but I want to understand what is being done and not make unnecessary changes.

    All that said, my questions are:

    1. I have a 200A main panel. If my backfed breaker is 40A, do I need to derate the main? My understanding is that NEC says that I can install up to 120% of of the Main rating so it looks like 40A is acceptable with no derate.

    2. If AC amps from the microinverters is 32A or less, is a 40A breaker at the main sufficient? (note: I am only planning for 23-28 amps)

    3. If I have OCPDs (2 20A breakers) on the roof in a combiner box, do I need another sub panel? or can I just wire direct from the combiner box to the PV meter? If I can, is it okay to transition from the 12 AWG wire in the engage cable to 6AWG romex/NM-B for the run to the PV Meter.

    4. Does anyone know if the GE kv2cs meter is acceptable to APS as a PV meter?

    5. Last question, It appears from reading APS's documentation that my disconnect needs to be at least a 2p 60A nonfusable. Would a D Square DU222RB meet that criteria? If it does, is it sufficient for my service, or do I somehow need larger because of the larger SES main size?

    Thank you in advance for you assistance..

  • #2
    Originally posted by SCA ESQ View Post
    I am in Phoenix, AZ, USA and I am planning a solar self-install on my roof using Enphase microinverters with a grid tie installation of 6.2-6.6 KW.
    My utility (APS) requires that I install both a Solar meter and a disconnect. I'm trying to figure the specifics of my system and have a few questions.

    To start off, I want to say that I know it is ultimately up to the exact conditions of my home and the opinion of the AHJ whether or not something is acceptable and meets code. Also, when it comes to actually working on the Main SES, I will hire an electrician, but I want to understand what is being done and not make unnecessary changes.

    All that said, my questions are:

    1. I have a 200A main panel. If my backfed breaker is 40A, do I need to derate the main? My understanding is that NEC says that I can install up to 120% of of the Main rating so it looks like 40A is acceptable with no derate.

    2. If AC amps from the microinverters is 32A or less, is a 40A breaker at the main sufficient? (note: I am only planning for 23-28 amps)

    3. If I have OCPDs (2 20A breakers) on the roof in a combiner box, do I need another sub panel? or can I just wire direct from the combiner box to the PV meter? If I can, is it okay to transition from the 12 AWG wire in the engage cable to 6AWG romex/NM-B for the run to the PV Meter.

    4. Does anyone know if the GE kv2cs meter is acceptable to APS as a PV meter?

    5. Last question, It appears from reading APS's documentation that my disconnect needs to be at least a 2p 60A nonfusable. Would a D Square DU222RB meet that criteria? If it does, is it sufficient for my service, or do I somehow need larger because of the larger SES main size?

    Thank you in advance for you assistance..
    0. Has Phoenix adopted the 2014 NEC? The choice is not made at the state level in AZ. I will assume [2014] below.

    1. Yes.

    2. Yes, on the AC side. Any overcurrent protection on the DC side must first multiply the STC current total by 1.25 to allow for exceptional production events (cloud fringe, low temp, high altitude, etc.) and that result must then be multiplied by 1.25 because the current is continuous. You have correctly multiplied 32 by 1.25 to get 40.

    3. You need a single disconnect (circuit breakers or fused disconnect at the point where the dedicated inverter output hits the house wiring. That would rule out just running the output of breakers at the inverters to the load side of the POCO meter. But since you appear to be talking about a separate production meter, the single disconnect would have to be on the supply side of that meter.

    4. No idea.

    5. Are you sure whether they are not referring to a minimum size of the main breaker (service size?) rather than the size of the backfeed breaker for PV AC? IF the former, you have a 200A service with a 200A main breaker, which would be OK.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

    Comment


    • #3
      Phoenix is still on the 2011 NEC.

      Re 3. I am wondering if I this proposed setup will work for my system: PV Modules --> microinverters-->engage cable--> AC combiner box with 2 20A circuit breakers and appropriate bus bar-->romex wire through attic--->PV meter--->AC disconnect--->Main SES.

      Does that meet code requirements? or do I have to install a sub panel between the Romex and the PV meter?

      Re 5: I specifically was reading this document https://www.aps.com/library/dg/suppl...quirements.pdf and wondering if the minimum 60A disconnect it mentions means that I need a 60A disconnect for my 40A backfeed or if I need to look for a 200A disconnect because of my 200A Main SES.

      Comment


      • #4
        Re 4: My 3 year old system was installed with a mechanical production meter. Some months later APS replaced it with an Elster electronic meter that's a different model from the main meter. Apparently APS likes Elster so you'd have to check with them to see if the GE would suffice.

        Comment


        • #5
          I am doing a self install with APS also

          Looks like Questions 1 and 2 have solid answers
          1 Sum of MAIN and PV BREAKER can not exceed 120% of bus rating
          2 PV BREAKER will be 125% over total rated inverter output or outputs. My example is 32 amps from a sma 7700TL-22 so a 32 X 125%= 40 Amp breaker
          3 Not much help here as I am doing a different setup but I think inspectors like EMT or MC over Romex... I could be way off here.
          4 APS will provide the production meter. Just need a meter socket jumper for testing. I think when they bring out the Bi Directional meter they slap your old one in your solar meter socket.
          5 The Square D DU222RB is a listed disco on the APS site. Its perfect for your application.
          6 If you haven't already you need to set up an Installer/dealer account with APS. Separate login from your home account with a separate email.
          30 SW310XL SB7700
          20 SW320XL SB5000

          Comment


          • #6
            Thank you both for your responses. That is some solid information. Especially on 4. and 5.

            I do already have an installer account setup. Though I'm still waiting for APS to respond to my email requesting they configure it as a self installer account.

            I have been reading everything APS has available on their website about interconnection and this pdf https://www.aps.com/library/dg/suppl...quirements.pdf talks about requiring a two disconnect configuration. I get that one is the external disconnect i.e. the Square D unit I mentioned earlier, but I am unclear on what the second one is. Is that the backfed breaker in my main panel, is it a breaker in a separate panel or is it something else entirely?

            edit: left out a comma and doubled a word
            Last edited by SCA ESQ; 09-24-2015, 12:08 PM. Reason: left out a comma and doubled a word

            Comment


            • #7
              Originally posted by SCA ESQ View Post
              Thank you both for your responses. That is some solid information. Especially on 4. and 5.

              I do already have an installer account setup. Though I'm still waiting for APS to respond to my email requesting they configure it as a self installer account.

              I have been reading everything APS has available on their website about interconnection and this pdf https://www.aps.com/library/dg/suppl...quirements.pdf talks about requiring a two disconnect configuration. I get that one is the external disconnect i.e. the Square D unit I mentioned earlier, but I am unclear on what the second one is. Is that the backfed breaker in my main panel, is it a breaker in a separate panel or is it something else entirely?

              edit: left out a comma and doubled a word
              That is only for a Line side tap. Where you would bypass your service panel and go right to the incoming feed.

              If you doing a load side connection (back feeding a breaker in your panel) then just a single 2 pole unfused saftey switch is required.
              30 SW310XL SB7700
              20 SW320XL SB5000

              Comment


              • #8
                Ah..Got it. Learning all these terms is like learning a whole new language. Thank you again.

                Comment


                • #9
                  Be careful in using the SQ-D DUxxxRB type AC disconnects. If you read the fine print on the label on the back of the cover, it states that the AIR rating is only good when the device is in series with fuses not breakers. Since these disconnects are required to be the fuseless type, technically you would have to put another fused device in series with them to be code approved. Not many inspectors know about this detail, but some do and enforce it and I believe Phoenix does. The solution is to use the EATON equivalent disconnect like a DG-222URB which does its testing using breakers as well as fuses. I still don't quite understand why the 10,000A AIR rating is even an issue in residential panels, but Be Safe - this is a heads up!
                  BSEE, R11, NABCEP, Chevy BoltEV, >2000kW installed

                  Comment


                  • #10
                    I did not know that, but that is part of the reason that I asked. I guess I'll go with an Eaton model instead. Thanks for the heads up.

                    Since you seem to know some info about NEC code and Phoenix's inspection policy, can you tell me if my question 3 in the original post is code compliant? I made a diagram (Meter Detail 2.jpg) of what I mean. Notice no sub panel - just cable from the attic. The cable in the attic running to a Soladeck AC combiner (with circuit breakers) on the roof.

                    Comment


                    • #11
                      Yes, your diagram looks ok (and inetdog has it right) except another little known rule (not often enforced) that you should have 8" of clearance around the disconnect handle to allow for a firefighter (with big gloves on) to operate it. Be sure to enter into the service panel below any active components inside (thats why the knockouts are all on the bottom) and also have 36" of clear, flat ground in front of all equipment to accommodate safe servicing of it.

                      Be aware that your utility (APS) will use this opportunity of having to sign off on your solar job as a way of forcing you to bring your service up to their latest requirements.
                      BSEE, R11, NABCEP, Chevy BoltEV, >2000kW installed

                      Comment


                      • #12
                        Well I made a new diagram Meter Detail 3.jpg. I didn't actually change the conduit on the main SES because there is a knockout there on the side. Which brings me to the next question - you mentioned APS will make me meet their latest requirements, my main panel is about 20 years old - as near as I can tell (no printed markings extant) it is a Murray panel. Is it likely that I will have to replace my main panel to get APS approval?

                        Comment


                        • #13
                          No, APS will not make you change your old Murray panel, but you know - electrical equipment doesn't last forever and for safety's sake, it might be a good idea to change out breakers, switches and outlets, etc every 50 years or so whether they need it or not.....
                          BSEE, R11, NABCEP, Chevy BoltEV, >2000kW installed

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