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Voltage on one lead of solar panel/string

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  • Voltage on one lead of solar panel/string

    Can someone explain what the voltage on one lead (+ or -) of a solar panel/string is?
    Obviously testing voltage from one lead to the other is Voc.
    From experience, testing voltage from one lead to ground shows a small initial voltage which quickly dissipates to 0. Does this mean that touching the bare conductor from one lead of a panel (or string) presents no shock hazard?

  • #2
    Depends on the voltage level. OSHA has stated that anything below 50VDC is safe to touch and will not hurt someone due to the high body resistance between the voltage source and ground. But if you shorted out a 12V battery + and - terminal you would see fireworks that could burn or even kill you.


    • #3
      When you touch/measure voltage from one lead to the frame of an otherwise unconnected
      panel, you do not have a complete circuit. Therefore you will not be able to draw any
      continuous current. Connecting a very high input impedance voltmeter might give an
      initial reading of voltage but no current/power. This is caused by static charge or extremely
      small leakage of the insulation, charging minute stray capacity with a few electrons. The
      energy content is less than you get rubbing your feet on the rug.

      Most single panels do not develop enough voltage between leads to be dangerous. Strings
      of panels can be very dangerous, mine run at 400VDC. Bruce Roe


      • #4
        Thank you all for responding! I would like to follow up with a video showing voltage testing to ground from one lead of the module. Can anyone provide explanation for these results?


        • #5
          Unable to play video. Anybody else?
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024


          • #6
            testing from a PV wire to ground is not a valid test
            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A



            • #7
              Originally posted by ttpvt1 View Post
              Thank you all for responding! I would like to follow up with a video showing voltage testing to ground from one lead of the module. Can anyone provide explanation for these results?



              You may have yourself a pinched wire somewhere in the installation. I'd go check each module where the frame comes in contact with the ballast for the string you're picking this up on.


              • #8
                A voltmeter is for measuring the difference in potential between points (nodes) in a circuit. A circuit
                is a connected arrangement of legitimate electrical components. The active elements of a panel are
                not connected to the frame. Unless they are connected externally (apparently not in this case) you
                do not have a circuit, so a so called measurement is meaningless.

                What is happening here, is there is a very small amount of capacity (because nothing is perfect
                without any slight unintended effects) exists between the panel elements and the frame. Something
                like static electricity has put a few electrons into the cap giving a voltage. A (digital) meter with half
                a dozen orders of magnitude higher impedance than needed for this work is connected and detects
                this arbitrary voltage. But even this meter draws a few electrons to make the measurement, which
                slowly discharges the cap, so the voltage heads slowly down.

                This job does does not require lab level resolution or impedance, a plain old self powered swinging
                needle meter would instantly drain the static charge to read zero with adequate resolution. I use
                light bulbs on my array, just like I did on power distribution good/bad at work. It would be really cool
                if that digital screen lit up, THIS IS NOT A LEGITIMATE CIRCUIT. Bruce Roe