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8400w Grid Tie System - Kit or piece it together?

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  • I think I'm on track now.

    Here is another question... I think I may have wasted some coin on fuse holders for the dc conductors.

    I will have 3 strings of panels (9 panels in series each) feeding 3 separate MPPT inputs on the inverter. Since none of the strings parallel with another outside of the inverter, do I even need fusing on the DC side?

    I had it in my head that because I had 3 strings... a fault on 1 could leave the other 2 feeding that fault and put me over the limit for requiring OCP... but each string will technically be kept separate as the inverter has 3 MPPTs and 3 separate inputs for them.

    Do I need fuses on the DC side in this case?

    Comment


    • This monster showed up today.
      IMG_20180419_112251769 by acidburn02zts, on Flickr

      IMG_20180419_112339283 by acidburn02zts, on Flickr

      Planning on getting it mounted tonight and finish up the AC wiring once the taps get here. 4 pallets of panels and racking are due to show up early next week and then the real work begins.

      Comment


      • Originally posted by Mr4btTahoe View Post
        I think I'm on track now.

        Here is another question... I think I may have wasted some coin on fuse holders for the dc conductors.

        I will have 3 strings of panels (9 panels in series each) feeding 3 separate MPPT inputs on the inverter. Since none of the strings parallel with another outside of the inverter, do I even need fusing on the DC side?

        I had it in my head that because I had 3 strings... a fault on 1 could leave the other 2 feeding that fault and put me over the limit for requiring OCP... but each string will technically be kept separate as the inverter has 3 MPPTs and 3 separate inputs for them.

        Do I need fuses on the DC side in this case?
        Nope. You can put up to two strings in parallel without needing to use any fusing. I don't have my NEC 2017 handy, but I recall it explicitly noting that PV sources are inherently current-limited and establishing the two-string upper limit for no fusing.

        I confirmed that current-limited business by accident a month or so ago by leaving my multimeter in the "Amperes" mode when trying to check the voltage on a string under full sun. There was a pretty dramatic arc from the PV positive making a sudden connection to PV negative through the test lead, due to the 300+ VDC involved, but the current flow never blew the 10A fuse in the multimeter. And that's from a string of PV panels that produces over 3000W under maximum-power point operating conditions.

        One thing to be aware of, though: For a PV connection that is not solidly grounded (and the inputs to the SunnyBoy almost certainly are functionally grounded instead), you need a PV disconnect switch to each MPPT input that breaks both poles of the connection, positive and negative.

        Comment


        • A disconnect other then the built in DC disconnect on the inverter? The SB7.7 has a main DC disconnect and nothing in the wiring portion of the diagram about adding additional disconnects unless a RSD is required.

          Is the built in disconnect enough?

          If you can, post the code for reference.

          One of the big reasons I went with this inverter was the GFCI, afci, and DC disconnect are all integrated. Would be disappointing to have to buy more equipment.
          Last edited by Mr4btTahoe; 04-20-2018, 01:15 AM.

          Comment


          • Originally posted by Mr4btTahoe View Post
            A disconnect other then the built in DC disconnect on the inverter? The SB7.7 has a main DC disconnect and nothing in the wiring portion of the diagram about adding additional disconnects unless a RSD is required.

            Is the built in disconnect enough?

            If you can, post the code for reference.

            One of the big reasons I went with this inverter was the GFCI, afci, and DC disconnect are all integrated. Would be disappointing to have to buy more equipment.
            Yes, if it has a built-in DC disconnect that breaks contact on both poles (positive and negative), then you're good. I mention this because I know of one charge controller (not quite the same as a grid-tied inverter, but still has the same PV connection requirements) with a built-in DC disconnect that doesn't meet this requirement. I'm guessing yours does given that it has all that other code-related stuff, but it would be good to check.

            The requirement is under the photovoltaic power systems section of the NEC where you will find such delights as GFCI, AFCI, and rapid shutdown. I don't recall the code reference, but it's easy enough to just Google it using those terms. The Mike Holt form is a great place for code -related information as well. You won't be able to post there, and neither am I, but I've learned a lot from reading the smart questions from licensed electricians and the answers provided.

            Comment


            • Originally posted by BackwoodsEE View Post

              Yes, if it has a built-in DC disconnect that breaks contact on both poles (positive and negative), then you're good. I mention this because I know of one charge controller (not quite the same as a grid-tied inverter, but still has the same PV connection requirements) with a built-in DC disconnect that doesn't meet this requirement. I'm guessing yours does given that it has all that other code-related stuff, but it would be good to check.

              The requirement is under the photovoltaic power systems section of the NEC where you will find such delights as GFCI, AFCI, and rapid shutdown. I don't recall the code reference, but it's easy enough to just Google it using those terms. The Mike Holt form is a great place for code -related information as well. You won't be able to post there, and neither am I, but I've learned a lot from reading the smart questions from licensed electricians and the answers provided.
              It doesn't specify anything other then it has a "built-in DC Disconnect Load Break Switch". Based on that, I'd say it disconnects both the + and - conductors at the switch since as you said, everything else that is required for code compliance is built in.

              I have been tossing around the idea of an additional disconnect on the roof.. but it isn't required in my area and I'm not sure if I want to add more complications or potential trouble spots to the system or not. It wouldn't be difficult to add it in after the fact if I chose to though...

              I discovered that I made a bad call on code with wiring up the AC side of the system. I used all 8awg THHN wire. Went to the big box store to get red, green, white, and black. All they had in stock was black and thinking I could just color code them with vinyl tape.. got all black.

              Now after some digging, discovered that anything 6awg or smaller can't be marked with tape or paint.. must be the actual jacket color.. and the ground must be green.. neutral must be white or grey. Back to the store to pick up the correct colors. It's a small oversight and since I hadn't ran the EGC to the roof yet, a cheap and easy fix... but just a note for those who may be reading this thread. NEC 200.6 says grounded conductors (neutral) must by white or grey. NEC 250.119 denotes mandatory ground colors.

              Small oversight but it can be a hold up.

              Comment


              • I don't have chapter & verse, but the Fire Dept wants a way to disconnect the HV DC when they roll up. If the inverter is inside, they won't like it. Your building inspector is also going to look for that too. I had to do it in Los Angeles county in 2004ish when I installed a 3Kw GT system, the inverter had a DC disconnect, but I had to add an outdoor one too.
                Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

                Comment


                • Originally posted by Mike90250 View Post
                  I don't have chapter & verse, but the Fire Dept wants a way to disconnect the HV DC when they roll up. If the inverter is inside, they won't like it. Your building inspector is also going to look for that too. I had to do it in Los Angeles county in 2004ish when I installed a 3Kw GT system, the inverter had a DC disconnect, but I had to add an outdoor one too.
                  Same situation here, they would not like it, and neither would I. Inverters are snug inside, but a
                  set of disconnects is outside that wall. Bruce Roe

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                  • Probably worth while to do it... I'll look into it more and see what it'll take.

                    Comment


                    • Had an idea today about having a dc disconnect accessible from outside.

                      Instead of adding more equipment, I think I'm going to cut the wall and add an access hatch to make the disconnect on the inverter accessible from outside. Being a pole barn, it would be fairly easy to do (cut sheet metal.. frame out the opening and make a hatch that is weather proof). Then clearly mark the hatch on the outside.

                      Would eliminate a component and give outside access to the disconnect.

                      Should satisfy their needs.

                      Comment


                      • Originally posted by Mr4btTahoe View Post
                        Had an idea today about having a dc disconnect accessible from outside.

                        Instead of adding more equipment, I think I'm going to cut the wall and add an access hatch to make the disconnect on the inverter accessible from outside. Being a pole barn, it would be fairly easy to do (cut sheet metal.. frame out the opening and make a hatch that is weather proof). Then clearly mark the hatch on the outside.
                        Doesn't sound aesthetically appealing to me.
                        And doesn't sound much cheaper either.

                        Since it's a pole barn it may not need a DC external disconnect. It's not a place where people are going to be living or sleeping - so check and see what the rules are.

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                        • Rest of the goodies showed up today. 2k lbs worth of racking, panels, etc...

                          IMG_20180423_123828319 by acidburn02zts, on Flickr

                          Now to get to work...

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                          • Everything is in order and ready to roll. Just got our approval from the POCO with a tentative generator start-up date of 5/18/18.

                            Plans are to have all the racking and grounding done by the end of the weekend. I made up some stuff to aid in lifting the panels to the roof. Have 50' of 5/16 poly with an eye in one end and a 6' 3/32" coated GAC sling with 3/16" carabiners on each end. I can hook to the factory holes in the panels and lift the panels to the roof with the poly.

                            I'll be laying out a "slide" of 18' 2x6s for the panels to slide up on as I pull them up. If I can get a few panels up and mounted each night after work, I should be able to pull it off.



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                            • Check with your utility company on both ac and dc disocnnect requirements. They are usually stricter than ahj, and ahj is usually stricter than code.

                              Also, regarding getting panels on the roof, consider renting a scissor lift. Best $400(monthly rental from a private party) on the solar project I ever spent. The amount of times up and down with materials, tools, plus the panels, was well worth the nominal project cost increase.

                              Comment


                              • Originally posted by ImInPhxAZ View Post
                                Check with your utility company on both ac and dc disocnnect requirements. They are usually stricter than ahj, and ahj is usually stricter than code.

                                Also, regarding getting panels on the roof, consider renting a scissor lift. Best $400(monthly rental from a private party) on the solar project I ever spent. The amount of times up and down with materials, tools, plus the panels, was well worth the nominal project cost increase.
                                As far as the requirements are concerned... all of that was handled months ago.

                                I considered renting a scissor lift, but the ground is too uneven to safely operate one. I'd have better luck with a bucket truck or similar but I believe the manual method will work out. It'll be a bit slower but with the pulley system I'm going to be using, it'll be fairly easy and give good control over the lift.

                                Starting on racking in the morning.

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