"wire" confusion

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al128
al128 Solar Expert Posts: 65 ✭✭✭✭
in Solar Beginners Corner #1
hi there,

non-native speaker alarm!

what type of "wire" do you use for PV systems?

- the "stranded?" wires (many tiny twisted up copper strands)
- the "solid" wire (basically one solid but thin (or not so thin) copper bar)

(could you name them correctly for me?)

does the "gauge" value only apply to the solid wire or also to the stranded?



my guess would be ... from the PVs to the CC and batt's the strandes ones (running 4.4A @ 60V in a string) ... and then from the batt to the inverter the solid one (say 100A @ 24V)

is it all a matter of gauge-value or does it also matter if the wire is solid or stranded?

any confirmations?
thx
al
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
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    Re: "wire" confusion

    you are correct that no matter if it is stranded or solid it is the same gauge and therefore equal to one another. you are also correct that a preference may be derived from the application as very large gauge wires that are stranded may be difficult to work with and stranded wires tend to take handling or wind when swinging in the air better than its solid counterpart.
    edit to add:
    they are the same if the metals used are also the same and not just the gauge being the same. #8 aluminum is vastly different from #8 copper. sometimes wires are plated with a different metal such as gold to stop corrosion, but if kept to the same gauge the gold influences the resistance. although gold on copper will be close to the same resistance you may find wires like copper on steel and the resistance is far higher than an all copper wire of the same gauge. the copper on steel is used in antennas to give the radio energy the low "skin" resistance while giving the strength of the steel for support. antennas are also a good place to have stranded wire for many reasons with the winds being an obvious one, but the area exposed to the air becomes a factor and gives it a larger "skin" area.
    not that it is important here, but i know somebody will ask what is a skin effect? it is the fact that radio waves flow better on the outer portions of wires than on the inside and it is more prevalent the higher in frequency that you go. some wires can be hollowed out and not impact the resistance of the radio waves flowing on it, but in solar this isn't the case as we just need low dc resistance to allow current to flow without much drop in the voltage. i'll end this here as i could keep going with this, but i've deviated enough.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,442 admin
    #3
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    Re: "wire" confusion

    Al,

    Solid wire works just fine for DC and low frequency AC circuits.

    Stranded wire, as Niel said, is used when flexing is possible.

    The finer the strands, the more flexing the copper wire will withstand before it "work hardens", then cracking/failing.

    If you have ever seen welding cables (use for electric "arc" welding)--they are very heavy cables with very fine wires.

    The one major problem I have had experienced with finely stranded cable is that its physical diameter is quite a bit larger than the diameter of solid copper cable.

    Because there is more "air space" in the fine cable--it requires larger crimp connectors and is more difficult to crimp correctly (and it is difficult to find the correct crimping connectors). Plus fine cable strands "wick up" water and other contaminants more easily--not good if your wiring will be wet or in weather).

    I would stay with solid or wiring with relatively thick strands unless there is an application where the cable needs to be very flexible (say a solar tracker).

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