Using a Square D QO Load Center for Combiner Box... pics and video..

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  • Dill
    Dill Solar Expert Posts: 170 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    In Minn you're in the same 1.3 factor zone as me: six panels in series will not work. The Voc will be way over the limit.

    There's a difference between one string or panel shorting and one shorting when it's got two (or more) others attached to it. Panels are capable of putting out their Isc under full light and short-circuit, and that is the maximum current their construction is designed to handle. The current will always take the path of least resistance. If that path is through an adjacent panel and that panel is only capable of Isc but the source is capable of 'X' * Isc then the shorted panel can literally burst into flames.

    A short in a panel (or string) that is on its own will not blow a fuse connecting it to the charge controller because the panel will cease to output current. However, there are things that can happen to a panel that will cause it to put out more than normal current that will blow a fuse. And there are things that can happen to a charge controller that will cause a short-circuit condition or back-feed battery current to the panel. That last one is pretty much "put out the flames and replace everything".

    thanks for the clarification. I am going to be adding 3 smaller panels to my Kyocera 135W panels, I will probably put one of the smaller panels (very close match in voltage specs) in series with one of the Kyoceras to make 3 strings, and fuse each string at my junction box. A fire would be the LAST thing I need right now...
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    Dill wrote: »
    thanks for the clarification. I am going to be adding 3 smaller panels to my Kyocera 135W panels, I will probably put one of the smaller panels (very close match in voltage specs) in series with one of the Kyoceras to make 3 strings, and fuse each string at my junction box. A fire would be the LAST thing I need right now...

    Okay now you introduced a new variable: different panels.
    Here you have to watch out because the same "overloading" can occur in the even of a short. In other words; if you have a string of Kyoceras with an Isc of, say, 8 and you connect a string of lesser Wattage panels that second string may have an Isc of, say, 5. Again you now have the possibility that the larger panels can push more current into the smaller panels than they can handle, even though there are only two strings of panels. So the Vmp matters for the parallel connection but in this instance you also have to look at the difference in Isc so that you don't have the same disaster potential as can happen with two strings pushing into a third (of the same type).

    I hope that wasn't too confusing.
  • Dill
    Dill Solar Expert Posts: 170 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    ah isn't this fun! I was saying series a Kyocera and one of the smaller panels and make 3 strings that way. Can you series 2 different panels like that? I got the idea from a post of yours in the past (used the search function)

    http://forum.solar-electric.com/showthread.php?15667-What-happen-if-doing-%283x24V-panels-in-parallel%29-then-series-with-1x12V-to-make-36V&highlight=strings+panels
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    Dill wrote: »
    ah isn't this fun! I was saying series a Kyocera and one of the smaller panels and make 3 strings that way. Can you series 2 different panels like that? I got the idea from a post of yours in the past (used the search function)

    http://forum.solar-electric.com/showthread.php?15667-What-happen-if-doing-%283x24V-panels-in-parallel%29-then-series-with-1x12V-to-make-36V&highlight=strings+panels

    Yes, you can. So long as the Imp is close enough. The Voltage doesn't matter, as it will add up. But if the Imp's are too far off the "smaller" one will limit the current of the larger and prevent it reaching full power.

    Yes, it is fun isn't it? Some of these formuli would make my old math teachers jump out a 3rd story window! :p
  • Dill
    Dill Solar Expert Posts: 170 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    Yes, you can. So long as the Imp is close enough. The Voltage doesn't matter, as it will add up. But if the Imp's are too far off the "smaller" one will limit the current of the larger and prevent it reaching full power.

    Yes, it is fun isn't it? Some of these formuli would make my old math teachers jump out a 3rd story window! :p

    so in that above post, wouldn't the 128W panel be limited by the 68W panel in series with it? My scenario will be adding 3 80W panels I'm acquiring from a friend to my 3 135W Kyos. Sounds like this might not work after all as the impp on the Kyo's is 7.63a and only 4.65a on the 80's. darnit.


    Sorry for the slight thread hijack Al, I will probably be using your idea at my cabin in the next month or so when I install my panels there. I am re-using my old Blue Sky 12v MPPT controller so all the panels will need to be paralleled as it only supports up to 35vdc from the panels.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    Dill wrote: »
    so in that above post, wouldn't the 128W panel be limited by the 68W panel in series with it? My scenario will be adding 3 80W panels I'm acquiring from a friend to my 3 135W Kyos. Sounds like this might not work after all as the impp on the Kyo's is 7.63a and only 4.65a on the 80's. darnit.

    That is what will happen: the KD135's output will be limited to 17.7 Vmp * 4.65 Amps or about 82 Watts.
  • Dill
    Dill Solar Expert Posts: 170 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    that's what I thought. I can't run them in their own 3 panel series either, so I guess I'll put them on my cabin up 'north' in parallel.
  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    Hate to be the code police, but...........................
    1.- The negative wire(s) should have a white maker on them.
    2.- This box will not pass NEC inspection, as the back-feed breakers must be bolted down.

    I am guilty of violating #2.:blush:
  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    n3qik wrote: »
    Hate to be the code police, but...........................
    1.- The negative wire(s) should have a white maker on them.
    2.- This box will not pass NEC inspection, as the back-feed breakers must be bolted down.

    I am guilty of violating #2.:blush:

    Um.. ok.. You do realize the red/black coming in was for this demo.. currently there is no wires in the box except the wires coming off the backbone/buss that head to the charge controller..

    The wire coming in will actually be whatever the standard 10AWG wire that comes on the MC4 type wire (I knows its black)..

    wind-sun_2209_38830677.jpg

    And I don't know if it matters as this is a DC panel not an AC panel... nothing AC is in this box..
  • silvertop
    silvertop Solar Expert Posts: 155 ✭✭✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    I like Square D QO load centers and breakers I used them for my c-60 controller and my 110 side, but just wanted to caution you about MPPT controllers. I have one array that runs aprox. 70-80 Volts ( wired 48 Volts) and my XW MPPT down converts to 24 Volt batt. bank. If I were using QO breakers I would be WAY over the QO 48 Volt limit. If you ever see this in your future......
  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    silvertop wrote: »
    I like Square D QO load centers and breakers I used them for my c-60 controller and my 110 side, but just wanted to caution you about MPPT controllers. I have one array that runs aprox. 70-80 Volts ( wired 48 Volts) and my XW MPPT down converts to 24 Volt batt. bank. If I were using QO breakers I would be WAY over the QO 48 Volt limit. If you ever see this in your future......

    In my OP I put this notice.. maybe you missed it.. I dunno.. >>

    QO breakers are rated for up to 48 VDC.. do not however try to use this in/with a 48 VDC rated panel..

    You can use this with 12v (17vdc usually) or 24v (30 and 37vdc) panels.. again do not exceed 48VDC..
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    The 48 VDC rating--In general, the UL ratings of stuff (when I used to use the stuff in products years ago) were always a bit unclear if these were "nominal" working voltages or never to exceed (i.e., there are 120 and 240 VAC rated fuses--But the normal maximum voltage for 120/240 is around 132/264 VAC).

    Interestingly, there appears to be no "legal/engineering" defined min/max grid voltage limits in the US. And those fuses/protective devices are perfectly OK to use on AC lines (from what I could find at the time).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    One of the significant differences between AC and DC: 'X' Volts DC really is 'X' Volts while 'X' Volts AC is RMS. This is why it is easier to interrupt AC than DC.

    A "48 Volt" array may have a Vmp of 70 Volts. The Square D QOU have a maximum DC Voltage rating of 60. I would not use them in that application. MidNite has DC breakers rated for 150 VDC which will work fine on such an array.
  • silvertop
    silvertop Solar Expert Posts: 155 ✭✭✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    I very much agree with Cariboocoot. I just received my Midnight Solar MNPV6 outdoor combiner box for my #3 array ,I think sometimes you need to be a little forward thinking about possible expansion. I have done my fair share of back tracking I just wanted to put this out there......8)
  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    I agree..

    Never use this Square D / Scheider box for more than a 24 VDC array setup.. the max is 48 VDC.. but you can't run 36 or 48 VDC panels..

    I did this for myself as I will never run more than a 24V array (at the max).. currently I am limiting myself to 12 VDC..

    Note I have used a 32VDC (60 Amp) max breaker on the side of the combiner (see bottom pic).. thats for the breaker to the controller..

    So that limits me entirely to 12v (17-18VDC) panels.. and not even 24v panels as they go from 30-38 VDC..

    I did this post for people whom may think no fuse/breakers are OK on a system, and use just a bussbar * 2 in a mini junction box..

    Which it is not OK to do..

    I am building this with my 10 yo son and explaining the limits of every component.. since the finished cabin will eventually be his..

    60AmpBrkrMounted.jpg
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    ywhic wrote: »
    I did this post for people whom may think no fuse/breakers are OK on a system, and use just a bussbar * 2 in a mini junction box..

    Which it is not OK to do..

    Let me jump in once again, and say, to meet code. For an awfully long time systems were setup with out fusing each panel or string of panels. There may be a small risk of over loading a panel, and a tiny risk of fire. I wouldn't do a roof mount with out fusing. But there is dang little risk of a serious fire, other than with homemade panels as the glass, silicon and even the backing are not particularly flammable. It was once a common practice to use a distribution block to combine panels and may solar companies still carry them.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Dill
    Dill Solar Expert Posts: 170 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    for a 12V or 24V system, couldn't you use something like a Blue Sea Systems blade fuse block, one for each panel? Then mount it in a waterproof box?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    Dill wrote: »
    for a 12V or 24V system, couldn't you use something like a Blue Sea Systems blade fuse block, one for each panel? Then mount it in a waterproof box?

    Functionally? Yes. In fact you may find very similar installs on RV's & campers and even cabins.

    There is sometimes a significant difference between what will work and what will pass code inspection.

    I rather thought the issue here was how many Volts DC you can put through the Square D breakers. That same issue comes up with "automotive" type fuses which are only rated for 32 Volts and therefore would not be a good choice for a "24 Volt" array which would have an actual Vmp of around 35.

    If you're installing safety devices of any sort it is paramount that they will actually function within the parameters of the system. Otherwise you have that "might work, might not" scenario which isn't safe. Worse, you might think it's safe when it isn't.
  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    You could.. and I did this 3 weeks back.. keep in mind more than likely they to are also rated for 32v max DC.. so 24v panels will not work as they are 29-37 vdc usually..

    IM000004.JPG

    I decided breakers and a real enclosure might be better.. and I can remove that 1 simple 60 amp breaker (as its rated at 32vDC).. and step right upto 24vDC rated panels..

    The little fuse block was $11 at autozone.. the 3R double gang box was about $10 with lid. thats already $20.. the Square D box for inside use is $20.. and the ourdoor is $37.. so therefore you'd have breakers (only $6 each) and some upgrade options..
  • Dill
    Dill Solar Expert Posts: 170 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    I think I'll use something similar to what Al did for my 12V system at my cabin, and do something a bit more robust for my higher voltage system at home. Thanks for opening my eyes on the safety aspects a bit.
  • solarNewb
    solarNewb Registered Users Posts: 2
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    ywhic wrote: »
    I did this for people who are new to solar and may be on a budget.. this case is indoor rated.. they do make a 3R rated version of this case.. wire used is 10AWG (to represent the solar panel wire) and 8AWG going to my charge controller.. The box was $20.. the outdoor box is $36 at MillsFleetFarm, HD, or Lowes..

    QO breakers are rated for up to 48 VDC.. do not however try to use this in/with a 48 VDC rated panel..

    You can use this with 12v (17vdc usually) or 24v (30 and 37vdc) panels.. again do not exceed 48VDC..

    You can series up to 2 of 12v panels (totals to 35vdc usually), or with singles of the 24vdc panels in parallel..

    Heres the basic QO612L100 box..

    QOCombiner1.jpg

    openbox.jpg

    Connect the backbone HOT/LOAD lugs so all the breakers will be combined.. (important to use 8AWG or heavier wire)

    I used 8AWG wire from HD (rated to about 70 amps).. I only need 60 amps..

    I went above with this 'connector' wire, some people go below with this wire..

    connectLOADhots.jpg

    We will be using the built-in neutral bussbar as our NEGATIVE/GROUND bar.. Its insulated from the case and LOAD.

    insertNEGController.jpg

    At this time REMOVE the little green screw that may be installed in the neutral busbar.. that goes thru the isolation plastic and into the metal casing.. this may/may not cause a shock from the NEGATIVE side of your solar PV array.. takes about 2 turns to remove.. this screw is used for ground and neutral bonding 110V AC applications.. which were NOT doing..

    NeutralBond.JPG

    Great idea using the combiner box. My question is about whether the fuses connected to the panel are connected in series. For instance, say I have 3 panels all at 12v each connected to a separate fuse - which are in turn connected to the back panel for the HOT and all negative/ground to the busbar. This is then outgoing voltage from the combiner box to say a charge controller...is this outgoing voltage a parallel or serial connection? i.e. is this 36v going out, or 12v?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    solarNewb wrote: »
    Great idea using the combiner box. My question is about whether the fuses connected to the panel are connected in series. For instance, say I have 3 panels all at 12v each connected to a separate fuse - which are in turn connected to the back panel for the HOT and all negative/ground to the busbar. This is then outgoing voltage from the combiner box to say a charge controller...is this outgoing voltage a parallel or serial connection? i.e. is this 36v going out, or 12v?

    If you connect all the negatives from multiple panels together the only possible combination is in parallel. This is the reason for the individual per-panel fuses; to protect against overloading a panel if it becomes shorted.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    Panels in series connection, you add the Volts of each panel, Amps do not add
    Panels in parallel connection you add the Amps of each panel, Volts do not add

    hth
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
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  • solarNewb
    solarNewb Registered Users Posts: 2
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    If you connect all the negatives from multiple panels together the only possible combination is in parallel. This is the reason for the individual per-panel fuses; to protect against overloading a panel if it becomes shorted.

    Thanks for this. The more I thought about it, I realized how obvious this was lol. Of course its parallel...I am connecting all negatives to the bus bar.
  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    I guess the nice side of most off-grid installs is that your not working for an inspector. Been beat up by inspectors a few times here by not using electrical devices in the application for which they are "listed". In other words, SQ-D did not intend for you to use a load panel as a DC combiner and did not test it for that - so you don't get to do that under the Code.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    solarix wrote: »
    I guess the nice side of most off-grid installs is that your not working for an inspector. Been beat up by inspectors a few times here by not using electrical devices in the application for which they are "listed". In other words, SQ-D did not intend for you to use a load panel as a DC combiner and did not test it for that - so you don't get to do that under the Code.

    Which is a little weird because when you think about it a combiner box is just a distribution box in reverse. Conductors do not care if they have AC or DC on them, so as long as the breakers used are DC rated there's no difference electrically.

    The big difference is that the D-box is not suitable for outdoor installation where combiner boxes are usually located. And that is a significant difference.
  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..

    There is a big difference between code rules and common sense, practicality, and will it work
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    solarix wrote: »
    There is a big difference between code rules and common sense, practicality, and will it work

    That's for sure! :D
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Using a Square D QO Load Center for Combiner Box... pics and video..
    solarix wrote: »
    There is a big difference between code rules and common sense, practicality, and will it work

    Amen! +1 on that post! :D
  • MC3
    MC3 Registered Users Posts: 1
    edited December 2016 #61
    Thank you for this information.  This is just a note to say that Square D QO and QOB breakers are not limited to 48 volts DC if they are used as described in Square D Data Bulletin  0601DB0401, though the use is not certified by Underwriter Labs, it is certified by Square D. The Data Bulletin is found here

    http://static.schneider-electric.us/docs/Circuit Protection/DC Rated Circuit Breakers/0601DB0401.pdf

    I called the phone number in the bulletin and confirmed that QO and QOB breakers can be used for up to 125 volts DC if used as described in the bulletin. A footnote and circuit diagram in the bulletin explain that the intent is that either two single pole breakers, or one double pole breaker, be used to break both the positive and negative DC lines (each getting its own breaker pole). I also confirmed something I had heard years ago, which is that Square D QO breakers will break DC current in either direction, that is, the breakers do not depend upon being wired in with any particular polarity.

    I am not sure, but I think other DC breakers need to be wired in with the greatest potential being wired to a specific side of the breaker (not so with Square D from what I was told). I have not used these breakers yet, but thought I would pass this on, as that bulletin is the only place I have seen that Square D QO and QOB breakers can be used for more than 48 volt DC circuits.