Wiring Question

shinybeast
shinybeast Registered Users Posts: 2
in Solar Beginners Corner #1
Hi, I was reading HandyBob's Blog, The RV Battery Charging Puzzle and saw this in the 'Wiring' section...

"Big wire is cheap compared to the cost of panels, so err on the big side. You can either run big wire or install multiple smaller runs and split the panels up into several feeds. DO NOT tie the wires together at both ends. One wire will always have less resistance & carry more of the load. Find a voltage drop chart and limit your loss from the roof to the batteries to 3%."

What does he mean about not tying the wires together at both ends? I have a bunch of #10 wire and was thinking of pairing two 15 ft. lengths to make each run of wire from two parallel panels to charge controller. Is that not a good idea? Is that what he's talking about?

Thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Wiring Question
    shinybeast wrote: »
    Hi, I was reading HandyBob's Blog, The RV Battery Charging Puzzle and saw this in the 'Wiring' section...

    "Big wire is cheap compared to the cost of panels, so err on the big side. You can either run big wire or install multiple smaller runs and split the panels up into several feeds. DO NOT tie the wires together at both ends. One wire will always have less resistance & carry more of the load. Find a voltage drop chart and limit your loss from the roof to the batteries to 3%."

    What does he mean about not tying the wires together at both ends? I have a bunch of #10 wire and was thinking of pairing two 15 ft. lengths to make each run of wire from two parallel panels to charge controller. Is that not a good idea? Is that what he's talking about?

    Thanks

    Not well-written but the sentiment is correct: you can not parallel small wires to increase current-carrying capacity. An example would be connecting two strands of 14 AWG at the same terminal of the power source and the same terminal of the load in order to carry 30 Amps of current. Use one strand of 10 AWG instead.

    So you either combine your panels 'on the roof' and run heavy gauge wire capable of handling the full current of all down to the charge controller, or you run individual sets of wires for the panels and combine at the charge controller. The latter is really messy and does not follow code of good conduct.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Wiring Question

    Oh and because there are nit-pickers out there who think "moderator" is a synonym for "target" ....

    NEC does allow paralleling of large gauge wire under certain conditions.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
    Re: Wiring Question
    Cariboocoot wrote: »
    Oh and because there are nit-pickers out there who think "moderator" is a synonym for "target" ....

    NEC does allow paralleling of large gauge wire under certain conditions.

    Is it not also permissible to parallel any other cable as long as it is to reduce voltage drop and not to increase ampacity? (The overcurrent protection must be for the thinnest cable in the parallel run).

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Wiring Question
    vtmaps wrote: »
    Is it not also permissible to parallel any other cable as long as it is to reduce voltage drop and not to increase ampacity? (The overcurrent protection must be for the thinnest cable in the parallel run).

    --vtMaps

    The way I read it the answer is "no". I'm not sure they'd make the distinction between the two functions as far as paralleling is concerned.

    This is not to say you won't find someone who will interpret it differently.

    As far as code of good practice is concerned it's 'not on' either way (even with independent fusing of the lines).
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