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Played with 400 volts DC last week.

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  • Played with 400 volts DC last week.

    Let me tell you. That stuff is no joke. It is far more dangerous than AC. Was troubleshoooting a photovoltaic array where I had no choice but to snip a negative line at a gutter. Though I was careful not ground out the conductor, the wire end still glowed, leaving the ends of the strands charred.
    For any apprentices out there, safety is paramount, as long as the sun is out there is no shutting the power off.

  • #2
    Re: Played with 400 volts DC last week.

    Originally posted by tailgunner View Post
    Let me tell you. That stuff is no joke. It is far more dangerous than AC. Was troubleshoooting a photovoltaic array where I had no choice but to snip a negative line at a gutter. Though I was careful not ground out the conductor, the wire end still glowed, leaving the ends of the strands charred.
    For any apprentices out there, safety is paramount, as long as the sun is out there is no shutting the power off.
    Yes, When dealing with voltages at this level it can certainly be lethal. It is true that DC is slightly more powerful than AC. (given same voltage and current)

    You had no choice than to snip a hot wire? Admittedly, I have not worked on PV systems.
    But I'd say there's always a way to isolate the power. Go and unplug each array if you have to.
    Why don't you have a disconnect per 690.13 and 690.17?

    It may be inconvenient, but there is always a way to do things safely.

    Comment


    • #3
      Re: Played with 400 volts DC last week.

      There is a DC disconnect between the array and the inverter which is Code of course. The problem was at the line side of the D/C. Remember, shutting off the disconnect does not shut off the line side, as long as there is daylight hitting the array, there will always be power. Thus demonstrates the hazards inherent with such systems.

      For this particular system. All the strings lead up to a gutter with EMT nipples that lead up into each DC disconnect, which then feeds the associated inverter. We had a problem where the solar tech crossed a set of wires when ended up half of a string to be tied into another one. Rather than pull a live negative conductor down a metal nipple, it was far safer to cut the wire at the gutter to swap the wires to the correct string. That's the thing with PV systems, it forces electricians to think "backwards" of sorts. Keep in mind, power is going toward to utility, not from it. When the problem is from the array to the D/C as in this case, there is no shutting it off.

      Comment


      • #4
        Re: Played with 400 volts DC last week.

        I understand. There are times its so much easier to just do things hot. ( Just make sure to have your 00 gloves on)

        I expected each pv panel to have a plug behind it that could be easily disconnected to debug.

        Not a bad idea to always "think backwards". When working on large control panels they often have power originating from different places.

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        • #5
          Re: Can you work on this before sunrise or in the evening?

          I would be concerned with 400 VDC.
          I'd take an educated guess - but I'm unqualified.
          It ain't just soot, it's paydirt.
          "I swear, wherever Gift goes, argument follows." -Youtube comment

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          • #6
            Re: Can you work on this before sunrise or in the evening?

            Originally posted by Robert Gift View Post
            I would be concerned with 400 VDC.
            Me too. But, I'm just as concerned using a chainsaw.

            Understanding and following the proper procedures (like using the proper PPE) is what matters.

            Comment


            • #7
              Re: Can you work on this before sunrise or in the evening?

              working with dc is a lot more dangerous than ac circuits
              even the lower voltages can hurt you if you are not careful.
              if your pv array is not equipped with plugs or a means of disconnect then you need to install disconnects rated for dc
              ac disconnects are not designed for dc and i highly recommend that you use the proper ones for it.
              cutting live conductors presents an arc flash situation that can be serious.
              i realize that occasionally we have to work with live circuits from time to time.
              but unless its absolutely unavoidable to shut the system down,
              ALWAYS ISOLATE ENERGY SOURCES! LOCK-OUT AND TAG-OUT!
              shooting the s*** is a lot more fun when you use hollow points (much more splatter)

              coffee hell gimme booze!!!

              Comment

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