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Thread: which cable is positive?

  1. #1
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    Default which cable is positive?

    Hello,

    I am in the process of installing a small solar array and ran my panel to charge controller cable through pvc - trouble is, I did not mark either of my two identical cables before pulling them through and now it is impossible to tell one from the other. This is 25' of large heavy cable that would be a long days work to take down, dismantle and mark it before re-assembly and remounting on my roof - so I'm hoping someone can tell me how to tell which cable is which.

    I'm thinking I can hook up both cables to my panels on the roof and use my multi-meter at the other end to see test which is positive and which is negative. How would I use the multi-meter to test for polarity?

    Thanks to all you smart people at there!

  2. #2
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    Quote Originally Posted by tday View Post

    I'm thinking I can hook up both cables to my panels on the roof and use my multi-meter at the other end to see test which is positive and which is negative. How would I use the multi-meter to test for polarity?

    Thanks to all you smart people at there!

    Thats the way i'd do it. If you look at your multimeter you can see a negative sign displayed when the polarity's are reversed. If not your going in the right direction.

  3. #3
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    Only your Meter knows.
    MSEE, PE

  4. #4
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    If you want a legal installation that conforms to code then the wires should be two different colors and the negative one should always be white. The positive can be any color but is usually black. If you do not care about the legal part and potential problems and liability and equipment damage to the inverter (miss matching the cables for a second with some inverters will fry them and this not covered by the warranty), then get a very long wire and attach it to one of the wires at one end of your run and then attach it to the leads at the other end and use a meter to check resistance. Once you have the correct ends identified then wrap each end with white electrical tape and make that your negative or neutral wire. The use of tape is according to code only for very large gauge wires.

    White wire does not cost any more than black so might as well do it right.

  5. #5
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    Quote Originally Posted by Elkhornsun View Post
    negative one should always be white. The positive can be any color but is usually black.
    Last chance for you to revise that statement or else a whole lot of pros will jump all over you with specs and standards.

    There is no color code standard for Solar PV panels like there is for AC systems. Only your volt meter will tell you the truth.
    MSEE, PE

  6. #6
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    Quote Originally Posted by Sunking View Post
    Last chance for you to revise that statement or else a whole lot of pros will jump all over you with specs and standards.

    There is no color code standard for Solar PV panels like there is for AC systems. Only your volt meter will tell you the truth.
    Actually there is a color code standard for DC PV systems, and as the NEC code book does not specify AC or DC the color code applies equally to both such systems.

    White for negative denotes this is a grounded system and the negative is grounded. Grounding the positive is also NEC compliant and would thus have a white wire carrying positive.

    If this is an ungrounded system (also compliant in some circumstances) then neither wire should be white. Red and black are acceptable colors to use.

  7. #7
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    Quote Originally Posted by ErnieM View Post
    Actually there is a color code standard for DC PV systems, and as the NEC code book does not specify AC or DC the color code applies equally to both such systems.

    White for negative denotes this is a grounded system and the negative is grounded. Grounding the positive is also NEC compliant and would thus have a white wire carrying positive.

    If this is an ungrounded system (also compliant in some circumstances) then neither wire should be white. Red and black are acceptable colors to use.
    But since some of the wires will be exposed to UV light from the sun, the only two colors you will eventually have are black (UV resistant) and white (starting white or bleached to look white). As a practical matter many systems use black for all wires and identify the ends (which will be protected from the sunlight) with colored tape, colored plastic rings, etc.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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