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  • #16

    Re: Solar disconnect wiring

    Re: Solar disconnect wiring

    A 150 Amp cable can use a 150 amp fuse and should carry a maximum of:
    • 150 amps * 0.80 NEC derating = 120 amps maximum continuous current

    You should have a couple extra fuses stored with the application...

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

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    • #17

      Re: Solar disconnect wiring

      Re: Solar disconnect wiring

      Thank you Bill.

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      • #18

        Re: Solar disconnect wiring

        Re: Solar disconnect wiring

        Here's a nit to pick.

        Originally posted by Vic View Post
        From the Midnite Forum, this FAQ adds some deatil, escpcially the polarity of the breaker that connects the output of a Charge Controller (MPPT) to the battery bank.
        http://midnitesolar.com/smf_forum/index.php?topic=113.0
        Vic
        I disagree with Halfcrazy (from Midnite) on one point:
        "In a PV combiner the + sign marked on the breaker connects to the PV positive output."

        Here is why:
        - "The + sign designates the highest potential should be conneced there."
        - "The main job of this output breaker is to trip when and if there is a catastrophic failure."
        - "Since these two terminals inside the charge controller are normally connected up to a very large battery bank, you have a direct short across the battery bank if the controller fails. During this condition, the controller is acting like a piece of wire."

        This says to me that the PV combiner breakers should be hooked up with the + marks towards the charge controller.( towards the inverter for batteryless) Because if one string in a multi-string installation has a fault it will receive current, backfed through the combiner circuit, with all available current from all of the other strings or by current comming from the battery via. a faulted charge controller.

        Alex Aragon

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        • #19

          Re: Solar disconnect wiring

          Re: Solar disconnect wiring

          I agree with Alex/SolaRevolution on that interpretation. The "excess" current source is the Solar Array common bus.

          -Bill
          20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

          Comment


          • #20

            Re: Solar disconnect wiring

            Re: Solar disconnect wiring

            Alex,

            To further pick a nit ...

            Quoting from the linked MN FAQ, "In a PV combiner the + sign marked on the breaker connects to the PV positive output. The same breaker when hooked up to the battery circuit (not in a PV combiner) hooks up a little different. The + sign hooks up to the battery plus".

            I read this to mean that in the case of the PV Combiner, the + breaker terminal is connected to the PV module's + wire. THE + on the PV module, NOT the CC's PV INPUT + terminal.

            So, IMHO, you and HC are in agreement. Vic
            Off-Grid, Sys1: 1280 AH 48 V bat, 5.250 KW STC PV, Classic 150, WBjr, MX-60, MN KID, Xantrex Stacked SW+ 5548s; EU6500isa, 21KW Kubota diesel gens, misc Honda Eu gens
            Sys2: 1280 AH 48 V 4KS25 Surrettes, 5.88 KW STC, Two Classic 150s, WBjr, MX-60, MN SPDs, Stacked X SW+ 5548s; Kohler 18 KW LP, EU 3000isa gens, HB DC Charger, Midnite Breakers/boxes. Thanks for this great Forum!

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            • #21

              Re: Solar disconnect wiring

              Re: Solar disconnect wiring

              Been mulling this interesting Q over and rereading both postings and a BF occurred when I read this part again...

              This is an easy one to determine in a PV combiner. Follow the current path through the combiner, into the PV input of a charge controller and out of the controller to an output breaker and then into the battery plus. You would think that the end of the output breaker connected to the controller would be at a higher potential than the battery plus. In normal operation this is true. The main job of this output breaker is to trip when and if there is a catastrophic failure.......During this condition, the controller is acting like a piece of wire. The battery positive terminal is the highest potential!

              It occurs to me, simply, that if one wants to Keep the Magic Smoke IN (think: in either the PVs or the Battery) the breaker + needs to be pointed towards the GREATEST CURRENT Potential... at whichever connecting point you are at, Combiner or Battery.

              the more I think about it the clearer it gets... but still a bit confusing
              Last edited by westbranch; March 25th, 2012, 11:04. Reason: incluce Bills clarification
              100% Off Grid @ 51* 46' N lat 124* 44' W long

              New House system: coming - 2 arrays @ 2240W
              CL150&Epanel 2 @140 W 12v PVs , 24V C&D AT-15P AGM @ 950Ah
              + CL150 2@120W 12 V panels, 24V C&D AT-15P AGM @ 950Ah Linksys wet54g - WiFi bridge
              Cotek ST1500W inverter, TBS 30a-24v Omni-charger, Honda Eu3000is,

              Guest cabin system: 3 - 70W panels to BS 2000e CC, with 2 - 100 ah 12v SAFT wet NiCd's , 600W TSW Inverter

              Comment


              • #22

                Re: Solar disconnect wiring

                Re: Solar disconnect wiring

                The greatest "Current Potential"... And what failures you are protecting against (down stream shorts overheating the wiring, etc.).

                -Bill
                20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

                Comment


                • #23

                  Re: Solar disconnect wiring

                  Re: Solar disconnect wiring

                  Originally posted by Vic View Post
                  Alex,

                  To further pick a nit ...

                  Quoting from the linked MN FAQ, "In a PV combiner the + sign marked on the breaker connects to the PV positive output. The same breaker when hooked up to the battery circuit (not in a PV combiner) hooks up a little different. The + sign hooks up to the battery plus".

                  I read this to mean that in the case of the PV Combiner, the + breaker terminal is connected to the PV module's + wire. THE + on the PV module, NOT the CC's PV INPUT + terminal.
                  So, IMHO, you and HC are in agreement. Vic
                  Vic,

                  I disagree with your statement that HC and I are in agreement.
                  The (+) labled side of the breaker needs to be connected to the CC side of the combiner, not the PV module's positive output.
                  See the diagram:
                  Name:  54eb810998fc0c91e4a4a3fbdba01a92.pdf
Views: 1
Size:  145.5 KB

                  Alex

                  Comment


                  • #24

                    Re: Solar disconnect wiring

                    Re: Solar disconnect wiring

                    Originally posted by SolaRevolution View Post
                    Vic,

                    The (+) labled side of the breaker needs to be connected to the CC side of the combiner, not the PV module's positive output.

                    Alex
                    Alex is this true where there is a battery vs a GT?

                    As I see it, in a battery system, if/when there is a breaker at/near the battery this eliminates the need for the + to point towards the CC. that is, if the battery breaker trips the CC becomes a null current device, ie no potential as the path is broken and the potential is now the PVs.
                    Eric
                    100% Off Grid @ 51* 46' N lat 124* 44' W long

                    New House system: coming - 2 arrays @ 2240W
                    CL150&Epanel 2 @140 W 12v PVs , 24V C&D AT-15P AGM @ 950Ah
                    + CL150 2@120W 12 V panels, 24V C&D AT-15P AGM @ 950Ah Linksys wet54g - WiFi bridge
                    Cotek ST1500W inverter, TBS 30a-24v Omni-charger, Honda Eu3000is,

                    Guest cabin system: 3 - 70W panels to BS 2000e CC, with 2 - 100 ah 12v SAFT wet NiCd's , 600W TSW Inverter

                    Comment


                    • #25

                      Re: Solar disconnect wiring

                      Re: Solar disconnect wiring

                      Originally posted by westbranch View Post

                      As I see it, in a battery system, if/when there is a breaker at/near the battery this eliminates the need for the + to point towards the CC. that is, if the battery breaker trips the CC becomes a null current device, ie no potential as the path is broken and the potential is now the PVs.
                      Eric
                      Well, it is possible that a fault in the combiner output circuit could receive fault current back-fed from the battery via the CC. This is quite possible with a PWM charge controller even while it is working properly. It is my understanding that an MPPT CC would not backfeed current unless there is a major malfunction in the CC. With the MPPT CC, the CC to battery wiring is going to have a higher current rating than the PV to CC wiring. The CC/battery breaker is too high of a current rating to properly protect the PV/CC wiring. A wire with an oversized breaker on it can do a lot of arcing without tripping the over-rated breaker. It does seem unlikely for a fault to occur in both the CC and the PV output circuit at the same time except for the case when one may cause the other.

                      The more common and likely hazard is the failed PV module. Panels have failed for no apparent reasons and others have been broken by bullets, arrows, baseballs, tree branches, horses, elk, bicycles, idiots...
                      The circuits in the PV modules usually have a current rating of +/- 15 amps. (some as low as 6 amps) There is no way for the output current of a string of PV modules to trip it's own overcurrent protection. The only way for the overcurrent protection to trip is by being back fed from other parallel strings or from a CC fault.

                      Imagine if the PV module in the pictures below were in a system with 6 parallel strings. The fault current could be more than 3 times the fuse rating of the module. If it was a 100kw GT system it could be +50 times the fuse rating with a high volt DC arc. You probably would not use breakes in such a system but you may very well have multiple combiner devices with similar fault direction issues.

                      Name:  3f08247d74f6dc68742b0fa43448300d.jpg
Views: 1
Size:  41.9 KBName:  cc72b7c9581351cf821a78f2bcb24695.jpg
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                      Alex

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                      • #26

                        Re: Solar disconnect wiring

                        Re: Solar disconnect wiring

                        OK, so what I said needs to have an addition at the end

                        " If/when The PVs become a current source and as this potential has nowhere to go, it can back-feed the parallel panels, so the + breaker side must point towards the PV disconnect. "
                        100% Off Grid @ 51* 46' N lat 124* 44' W long

                        New House system: coming - 2 arrays @ 2240W
                        CL150&Epanel 2 @140 W 12v PVs , 24V C&D AT-15P AGM @ 950Ah
                        + CL150 2@120W 12 V panels, 24V C&D AT-15P AGM @ 950Ah Linksys wet54g - WiFi bridge
                        Cotek ST1500W inverter, TBS 30a-24v Omni-charger, Honda Eu3000is,

                        Guest cabin system: 3 - 70W panels to BS 2000e CC, with 2 - 100 ah 12v SAFT wet NiCd's , 600W TSW Inverter

                        Comment


                        • #27

                          Re: Solar disconnect wiring

                          Re: Solar disconnect wiring

                          I think we are on the same page, Eric.

                          Check out this pic of a failed string. This could never happen unless this burned up string was receiving parallel current.
                          http://www.curcap.com/wp-content/upl...anelfire_2.jpg

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