Wiring for 25 amps? what's the safest size

Urbandialect
Urbandialect Solar Expert Posts: 107 ✭✭✭✭
in Solar Beginners Corner #1
I have 7 55watt (home made) panels ... I'm wiring them all into a combiner box i made, each panel is about 3 to 3.5 amps a piece, so I'm coming out of the combiner box around 20 to 25 amps, I have about 80 feet of 14 gauge Romex wire i got for free, the distance between array and charge controller is about 15-20 feet.. Can i use 14 gauge wire to run 25 amps from combiner box to charge controller without burning the wire? The fuses I'm using are 5 amps they are on the positive leads of each panel coming into the postive bus bar in the combiner box.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
    Re: Wiring for 25 amps? what's the safest size
    Urbandialect wrote: »
    I have 7 55watt (home made) panels ... I'm wiring them all into a combiner box i made, each panel is about 3 to 3.5 amps a piece, so I'm coming out of the combiner box around 20 to 25 amps, I have about 80 feet of 14 gauge Romex wire i got for free, the distance between array and charge controller is about 15-20 feet.. Can i use 14 gauge wire to run 25 amps from combiner box to charge controller without burning the wire? The fuses I'm using are 5 amps they are on the positive leads of each panel coming into the postive bus bar in the combiner box.

    Even if you did get away with it, you'd have major losses in that wire. Definitely not recommended even if it didn't burn the wire. I won't ask about the panels.
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  • Urbandialect
    Urbandialect Solar Expert Posts: 107 ✭✭✭✭
    #3
    Re: Wiring for 25 amps? what's the safest size
    waynefromnscanada wrote: »
    Even if you did get away with it, you'd have major losses in that wire. Definitely not recommended even if it didn't burn the wire. I won't ask about the panels.

    Dang it, I'm trying to get out of buying 10 and 8 gauge wire, Somebody tell me that 14 gauge wire can handle 25 amps w/no problem.

    Far as lossing power from the wire? that is fine, I'm coming out at 20 volts, it's cool long as i don't drop below 16 volts b4 i get to charge controller, and I'm pushing it on the amps doe, that's why lossing power is a good thing, the PWM controller is rated for 25 amps, if i get one of those days where the array put out it's full power 3.8 amps, i could end up w/26.6 amps which could fry the charge controller, I doubt going over by 1 amp can fry it, but it is a cheap charge controller, so I don't know, it might really be a 20 amp rated at 25 amps.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Wiring for 25 amps? what's the safest size

    Short answer: no.

    14 AWG would be pushed to its limit at 20 Amps. It's typically used for 15 Amp household circuits you may note.
    Wayne's take on the V-drop is correct: looks like a 20% Voltage loss for that distance/Voltage/current. You're looking at 6 AWG before the V-drop is under control. This is why panels are often put in series and then run through an MPPT controller.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,654 admin
    #5
    Re: Wiring for 25 amps? what's the safest size

    For some reason, 14 AWG (by the numbers) should be good for 20 amps, and so on for 12 and 10 awg (I think).

    For some reason, that I could never find, NEC derates those first 2-3 standard gauge wires by ~5 amps.
    • 25 amps * 4 volt drop = 100 watt drop
    That is a fairly significant power loss...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #6
    Re: Wiring for 25 amps? what's the safest size

    Split it in half and run two runs @ 12.5a, probably still have the voltage drop. But I am no EE or electrician.
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  • Urbandialect
    Urbandialect Solar Expert Posts: 107 ✭✭✭✭
    #7
    Re: Wiring for 25 amps? what's the safest size
    Cariboocoot wrote: »
    Short answer: no.

    14 AWG would be pushed to its limit at 20 Amps. It's typically used for 15 Amp household circuits you may note.
    Wayne's take on the V-drop is correct: looks like a 20% Voltage loss for that distance/Voltage/current. You're looking at 6 AWG before the V-drop is under control. This is why panels are often put in series and then run through an MPPT controller.

    How did i know you where going to say that, ok 6 awg it is, i do have 20 feet of 0 gauge i got for free but it's too big to fit on the terminals of the charge controller and bus bar
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Wiring for 25 amps? what's the safest size

    If you divide it up as solar_dave suggested the V-drop goes down to a "mere" 10% per line (approximately). It's still fairly substantial, though.
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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    #9
    Re: Wiring for 25 amps? what's the safest size

    what would work, and how i did it since 14 gauge can be had rather cheap comparatively, is wire each panel to a combiner box closer to the base station with 14 gauge, i actually used 12 gauge, then use something heavy to tie to the controller and bank ..
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  • Urbandialect
    Urbandialect Solar Expert Posts: 107 ✭✭✭✭
    #10
    Re: Wiring for 25 amps? what's the safest size
    bsolar wrote: »
    what would work, and how i did it since 14 gauge can be had rather cheap comparatively, is wire each panel to a combiner box closer to the base station with 14 gauge, i actually used 12 gauge, then use something heavy to tie to the controller and bank ..

    Yeah, that's what i planned to do... I have 12 gauge coming off the panels about 6inches off each panel, connect the 12gauge to the 14 gauge and run it to the combiner box..and use the same 14 gauge from the combiner box to the charge controller, but the 14 awg is only rated for 20 amps :( And the 0 gauge is too big to fit
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #11
    Re: Wiring for 25 amps? what's the safest size
    Urbandialect wrote: »
    0 gauge i got for free but it's too big to fit on the terminals of the charge controller and bus bar

    Cartainly NOT best practice and possibly NOT to code and I'm sure people can come up with 10 reasons to NOT do this... but you could use the 0 guage and just trim off enough of the strands on the end to make it fit the terminal. I often did this with car stereo amp installations way back in the day.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #12
    Re: Wiring for 25 amps? what's the safest size
    techntrek wrote: »
    Cartainly NOT best practice and possibly NOT to code and I'm sure people can come up with 10 reasons to NOT do this... but you could use the 0 guage and just trim off enough of the strands on the end to make it fit the terminal. I often did this with car stereo amp installations way back in the day.

    I did that too, until the equipment I was using required the big stuff. I still have a couple of 25' spools of it in the garage. I think the correct way to use that type of thinking is to run the 1/0 as close as you can and then attach it to a busbar and run a short distance with a cable that would fit. Best of both worlds.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: Wiring for 25 amps? what's the safest size

    "Current choking." Yep. That's fun. The small bit acts like a fusable link and is the first place for trouble to start. If you use small bits of wire, it's neatly wrapped in flammable insulation too.

    If you're going to shrink cable sizes to fit terminals remember you will basically be doing so to push too much current through too small a conductor. Best to reduce it with a proper connecting lug and make attachments with solid metal. Like to a fuse block.
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  • raydias
    raydias Solar Expert Posts: 68 ✭✭✭✭
    #14
    Re: Wiring for 25 amps? what's the safest size

    I used a fused power distribution block that had 1/0 in and 4-8 gauge out. Look at Stinger SHD820 - HPM MIDI Fused Distribution Block

    You can find them all over on E-Bay, auto parts stores and audio stores.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,654 admin
    #15
    Re: Wiring for 25 amps? what's the safest size

    People do it all the time--Remember, here we have used larger gauge cable to reduce resistance of longer / low voltage runs.

    As long as the remaining cable that fits into the terminal block still meets the required gauge for carrying current (i.e., you had to trim it to 6 awg--but you are only carrying 20 amps any way)--it should not be a problem.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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