How do I determine the wire gauge from combiner box to charge controller?

showmeshowme Registered Users Posts: 63 ✭✭

You all are probably going to get tired of my questions before I'm done, but here's another question- I've got my wiring in place (not connected yet) for the first of two arrays. Although I've labeled it an 8kw system, at 320w per module, I've got to leave one off to even out the arrays to 12 each, so it's actually 7680w, with 3840w per array. I've got 4 strings of 3 panels, as suggested by those who've answered my questions, that will be going through a Midnite Solar 6 panel combiner box (each= I may add panels later), then going through MS classic 150. The return leads on my home run wires run 15' and under, and the distance from the combiner box on the array pole to the charge controllers is about 30' total path of the conduit.

My array wires are, of course, 10g, so what is the acceptable gauge for the combiner to cc wire? I'm thinking 6g. but I'd rather be safe than sorry.

While I'm asking, I've got another hypothetical question for a future run to the house. As of now, as I've said in other posts on this project, we're temporarily (until our house is built next spring/summer) installing all of our equipment in a shed I'm building between the arrays to be used during some of the construction and work on the property. After the house is built, I'll transfer as much of the equipment as is practical to the houses garage, which will be about 270' away from the "power house" and arrays. If I were to leave the solar chargers in the shed, what gauge wire would I need to use for that 270' run? Better yet, where can I find a reference that would allow me to figure this out myself? I really appreciate everyone's help on this forum, but as soon as I get a question answered I have another in the next phase. I'm starting to feel like a mooch. I've always been a DIY'er, but I hate to keep bugging you all with questions that probably seem trivial to you who know this stuff already. Thanks for any and all replies. Lee

"Knowing is not enough, we must apply. Willing is not enough, we must do."   Goethe

NOS Trace Xantrex power panel, (3) Trace Xantrex SW5548's (2 NOS in boxes, one used), Xantrex DC/disconnect, AC disconnect/conversion, Xantrex T240 Auto transformer, (3) C40 PWM charge controllers, (2 NOS, one used)  8k LG Neon 320w, (8)Evergreen  Solar 120w (960w)  , Bergey XL.1 1.5k genny, AirX 400 genny, 48v Interstate Workman batts (frozen/toast), (2) MT Solar Top of Pole 12's, (2) Midnite Solar MSPV 4 combiner boxes, (2) Midnite Solar Classic 150's and one nice Ozark hilltop to set them all.


Comments

  • PhotowhitPhotowhit Solar Expert Posts: 5,811 ✭✭✭✭✭
    In the end it's how much wire loss you can tolerate. Back in the days of expensive panels and somewhat cheaper wire we shot for <2%.

    Today with cheap panels, you might go a bit more. Higher voltage running from combiner box to charge controller (always should be close to battery bank) it's easier to keep within the 2%, but systems are more often over paneled these days so more rare to run at highest capacity.

    Either way, I'd just use a voltage drop calculator to see where you stand. At thos distances, I'd bet 10 gauge would be below 3% losses.

    Voltage Drop Calculator

    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.
  • SurfpathSurfpath Solar Expert Posts: 450 ✭✭✭
    I also recommend going a little bit bigger on the wiring. You never know when you’re going to upgrade your system in the future with more panels. We used six gauge originally in our system, and now wished we went with four.

    When you build your house and put in your conduit from the roof to the charge controller  also think about putting in slightly larger electrical conduit. You never know if you have to run thicker wires through the conduit, or more wires.
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • showmeshowme Registered Users Posts: 63 ✭✭
    Thanks, Surfpath. I've already got the 6 gauge installed, but it will be a temporary run, anyway. It has a 30' run from both arrays to the shed that will be the power plant until we get our house built. Then it will be a 260' run from to the house. I plan on using 4/0 welding cable for that, along with new conduit. I have the two 6 gauge pv wires and a 6 gauge bare ground wire running through 3/4" non metallic liquid tight conduit for the short temp run. I will definitely be using bigger, solid conduit pipe for the long run.

    "Knowing is not enough, we must apply. Willing is not enough, we must do."   Goethe

    NOS Trace Xantrex power panel, (3) Trace Xantrex SW5548's (2 NOS in boxes, one used), Xantrex DC/disconnect, AC disconnect/conversion, Xantrex T240 Auto transformer, (3) C40 PWM charge controllers, (2 NOS, one used)  8k LG Neon 320w, (8)Evergreen  Solar 120w (960w)  , Bergey XL.1 1.5k genny, AirX 400 genny, 48v Interstate Workman batts (frozen/toast), (2) MT Solar Top of Pole 12's, (2) Midnite Solar MSPV 4 combiner boxes, (2) Midnite Solar Classic 150's and one nice Ozark hilltop to set them all.


  • JarheadJarhead Registered Users Posts: 5 ✭✭
    showme said:

    You all are probably going to get tired of my questions before I'm done, but here's another question- I've got my wiring in place (not connected yet) for the first of two arrays. Although I've labeled it an 8kw system, at 320w per module, I've got to leave one off to even out the arrays to 12 each, so it's actually 7680w, with 3840w per array. I've got 4 strings of 3 panels, as suggested by those who've answered my questions, that will be going through a Midnite Solar 6 panel combiner box (each= I may add panels later), then going through MS classic 150. The return leads on my home run wires run 15' and under, and the distance from the combiner box on the array pole to the charge controllers is about 30' total path of the conduit.

    My array wires are, of course, 10g, so what is the acceptable gauge for the combiner to cc wire? I'm thinking 6g. but I'd rather be safe than sorry.

    While I'm asking, I've got another hypothetical question for a future run to the house. As of now, as I've said in other posts on this project, we're temporarily (until our house is built next spring/summer) installing all of our equipment in a shed I'm building between the arrays to be used during some of the construction and work on the property. After the house is built, I'll transfer as much of the equipment as is practical to the houses garage, which will be about 270' away from the "power house" and arrays. If I were to leave the solar chargers in the shed, what gauge wire would I need to use for that 270' run? Better yet, where can I find a reference that would allow me to figure this out myself? I really appreciate everyone's help on this forum, but as soon as I get a question answered I have another in the next phase. I'm starting to feel like a mooch. I've always been a DIY'er, but I hate to keep bugging you all with questions that probably seem trivial to you who know this stuff already. Thanks for any and all replies. Lee

    Go with #4 stranded copper if u can find ,always derate cable size by 20%
  • JarheadJarhead Registered Users Posts: 5 ✭✭
    Jarhead said:
    showme said:

    You all are probably going to get tired of my questions before I'm done, but here's another question- I've got my wiring in place (not connected yet) for the first of two arrays. Although I've labeled it an 8kw system, at 320w per module, I've got to leave one off to even out the arrays to 12 each, so it's actually 7680w, with 3840w per array. I've got 4 strings of 3 panels, as suggested by those who've answered my questions, that will be going through a Midnite Solar 6 panel combiner box (each= I may add panels later), then going through MS classic 150. The return leads on my home run wires run 15' and under, and the distance from the combiner box on the array pole to the charge controllers is about 30' total path of the conduit.

    My array wires are, of course, 10g, so what is the acceptable gauge for the combiner to cc wire? I'm thinking 6g. but I'd rather be safe than sorry.

    While I'm asking, I've got another hypothetical question for a future run to the house. As of now, as I've said in other posts on this project, we're temporarily (until our house is built next spring/summer) installing all of our equipment in a shed I'm building between the arrays to be used during some of the construction and work on the property. After the house is built, I'll transfer as much of the equipment as is practical to the houses garage, which will be about 270' away from the "power house" and arrays. If I were to leave the solar chargers in the shed, what gauge wire would I need to use for that 270' run? Better yet, where can I find a reference that would allow me to figure this out myself? I really appreciate everyone's help on this forum, but as soon as I get a question answered I have another in the next phase. I'm starting to feel like a mooch. I've always been a DIY'er, but I hate to keep bugging you all with questions that probably seem trivial to you who know this stuff already. Thanks for any and all replies. Lee

    Go with #4 stranded copper if u can find ,always derate cable size by 20%
    #2question the bigger the cable the smaller the voltage drop.if u can afford . voltage drop calculators can b googled b sure b4 u go 8kw can b carried by by#4 but #2 will have a smaller voltage drop over the run
  • BB.BB. Super Moderators, Administrators Posts: 32,612 admin
    edited March 10 #7
    Be careful with recommending AWG cable size by using Watts and KWatts... You really need to know the working voltage and current in the wiring to make the proper calculations for cable sizing.

    Also, "just going bigger" in cable AWG... Besides the high cost of copper, you can also run into other issues like cable will not fit into controller wiring terminals, and thick cables are very stiff and difficult to pull through bends and wire up in electrical boxes,

    -Bill

    PS: Also need to know wire run length to check voltage drop. Low voltages (especially 12 VDC), need very heavy cables to send a good amount of current distance from the battery bank.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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