Shocking question

solarvicsolarvic Solar Expert Posts: 1,043 ✭✭✭
While wireing 1 string of panels into my combiner box from 2 separate top of pole mounts I got shocked. What I had to do with the cables I had was cut off about 4 ft of cable off the end of one cable for the positive of 1 cable and 4 ft off the other cable with the neg. connection. That left me with 2 cables the right length but had to add some cable to connect the 2 short pieces together from the positive panel of one rack to the negative panel of the other rack. When I used the allen wrench to tighten the splicer I got jolted preety good and my arm still hurts a day later. I Didn,t have all the panels connected to each other to make the completed circuit but had most of them connected on each rack. I had the 2 short pieces of wire connected . So aparently you can still get shocked when you connect the positive from from one panel and the other wire connected to negative and connect a wire between the 2 wires. Didn,t take me too long to get those connections disconnected before I proceded putting in the splicer. I didn,t think you could get shocked on less all the panels were connected together to make the complete circuit. :cry:solarvic

Comments

  • jaggedbenjaggedben Solar Expert Posts: 228 ✭✭
    Re: Shocking question

    Sounds like maybe you had a ground fault type situation. That is, some path for current to go from a panel lead through you and back to the wire you were working on. If you had a panel unconnected but the connector were close enough to a piece of metal to arc, it's possible it could happen.

    In general it is best practice to do all splicing and terminating of wiring before plugging said wiring into any panels. That probably would have avoided your getting shocked.
  • peakbaggerpeakbagger Solar Expert Posts: 335 ✭✭✭
    Re: Shocking question

    Invest in a big tarp and cover the panels before wiring, either that or get a headlamp and do the connections at night. You were lucky you could let go, DC has a bad habit of making your muscles contract and staying that way.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Shocking question
    peakbagger wrote: »
    Invest in a big tarp and cover the panels before wiring, either that or get a headlamp and do the connections at night. You were lucky you could let go, DC has a bad habit of making your muscles contract and staying that way.
    Agree. Was thinking - - there could have been a funeral. Not kidding. Sometimes we forget, or don't realize the strength and power of the energy we are dealing with.
    Thanks for sharing you're experience with us solarvic, it should be a wake up call and reminder to all of us!
  • tmarchtmarch Solar Expert Posts: 143 ✭✭
    Re: Shocking question

    Some time ago I was doing an install that only took 4 panels so covered them with blankets and went to work wiring the combiner box etc. I was being cautious, but not overly cautious because I had them covered. When I finished I uncovered the panels and measured 193 volts at the combiner box, covered the panels again for some touch up work and measured them then just for curiosity, still over 160 volts. Lesson learned, don't use a opaque covering, best is a piece of cardboard taped tightly, and still use caution.
  • inetdoginetdog Solar Expert Posts: 3,121 ✭✭✭✭
    Re: Shocking question
    tmarch wrote: »
    Some time ago I was doing an install that only took 4 panels so covered them with blankets and went to work wiring the combiner box etc. I was being cautious, but not overly cautious because I had them covered. When I finished I uncovered the panels and measured 193 volts at the combiner box, covered the panels again for some touch up work and measured them then just for curiosity, still over 160 volts. Lesson learned, don't use a opaque covering, best is a piece of cardboard taped tightly, and still use caution.

    But did you measure the short circuit current with the panels covered? If the current is low enough, the shock might be felt but would not do damage. And the hazard of an arc in case of an accidental short would be much smaller. For the open circuit voltage to go down that much, the available power from the panels would have to be very small.
    Essentially what is happening is that the small amount of current being drawn by the voltmeter is pulling the voltage down. With a sensitive enough voltmeter, you will read full output voltage if there is any light at all.
    SMA SB 3000, old BP panels.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Shocking question

    Did you have the negative conductor for the string connected all the way back to the inverter? If so, that's what got you. The negative is (usually) connected to ground through a ground fault fuse or breaker inside the inverter, so there is a potential for shock between the positive end of the string you are wiring and the grounded racking. The ground fault fuse or breaker is there to prevent fires, not to protect you from shock (the set point is much too high current for that), so when you get zapped that way it won't open the circuit.

    That one has got me - once - as well. The good news is that a jolt like that is pretty strong aversion conditioning for the behavior that got you shocked. If it doesn't kill you, that is...

    Here's how it happened to me (I hasten to point out that I was very new to solar at the time and realize now that I did several things wrong) - a cautionary tale:

    I was debugging an array on an indoor training facility that had a dead string. Thin film modules, 480V string voltage, metal roof. With the inverter shut down and the fuses in the combiner box popped out, I checked the voltages on the fuse holder inputs and one of them showed no voltage. Suspecting the fuse holder, I removed the positive lead from the fuse holder on the suspect string and checked the bare wire. Again, no voltage.

    Here's what the root cause was: A poorly crimped MC4 connector on one of the home runs allowed the wire to be pulled (just barely) out of the connecting pin, opening the circuit. Minor movements of the conductors made this connection (or lack of it) intermittent.

    So anyway, after putzing around with the system for a while and still not yet finding the problem, I decided to reconnect the positive lead to the fuse block, but the prior connection to the block had spread the strands of the wire so that it wouldn't fit back in the hole in the block (my aversion conditioning is kicking in right now as I write this); I was wearing shorts and kneeling on the metal roof. Without thinking (and it was a dead wire, anyway, right?), I grabbed the bare conductor with my fingers to squeeze the strands together so they would fit into the hole. The next thing I know, I am lying on the floor with my heart pounding and ringing in my ears.

    Obviously, I screwed up. Between the time I measured the zero voltage on the conductor and when I grabbed the wire, my moving the wires around caused the intermittent open in the connector to close and put the entire string voltage on that wire, and the negative conductors of the array were connected to ground (and therefore the metal roof on which I was kneeling with my bare knees) through the GFI circuit. When I touched that wire I completed the circuit though my body.

    I was very lucky. It was an indoor mockup of a rooftop, so I only had a couple of feet to fall. The big stadium lights over the roof that we used for commissioning the system were off and the only illumination on the array was the normal fluorescent lighting in the building, so while the voltage was there, the available current was very low. Had I been outdoors and up on a real rooftop in bright sunlight, the outcome would probably have been very different and I very likely would not be writing this.

    Be careful out there.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Shocking question
    inetdog wrote: »
    But did you measure the short circuit current with the panels covered? If the current is low enough, the shock might be felt but would not do damage. And the hazard of an arc in case of an accidental short would be much smaller. For the open circuit voltage to go down that much, the available power from the panels would have to be very small.

    As little as 20 ma passing through the chest, can stop the heart. OUCH!
    One reason GFIs kick out @ 5 ma.
  • solarvicsolarvic Solar Expert Posts: 1,043 ✭✭✭
    Re: Shocking question

    GGUNN and all others. Some times learning the hard way really makes you be more carefull and safe if you don,t die first. My string of panels was the maximum amount for my 600 vdc inverter as called for in the string chart for my location. Not all of them were connected together yet to make the string .
    Mr GGunn I hadn,t even run the wire to the inverter yet so the shock came from the panels. The wires from the panels will be The last ones plugged together till all the other wireing is completed. Thanks everyone for the imput. :Dsolarvic:D
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Shocking question
    solarvic wrote: »
    GGUNN and all others. Some times learning the hard way really makes you be more carefull and safe if you don,t die first. My string of panels was the maximum amount for my 600 vdc inverter as called for in the string chart for my location. Not all of them were connected together yet to make the string .
    Mr GGunn I hadn,t even run the wire to the inverter yet so the shock came from the panels. The wires from the panels will be The last ones plugged together till all the other wireing is completed. Thanks everyone for the imput. :Dsolarvic:D
    Well, obviously there was a completed circuit somewhere. It's possible that the other cut end was making contact with the racking and you completed the circuit by touching the rack at the same time as the end you were working on. I'm glad you're OK.
  • solarvicsolarvic Solar Expert Posts: 1,043 ✭✭✭
    Re: Shocking question

    What I think happened. I needed about 25 foot cables with male and female ends to connect to my combiner box from 2 separste TOP racks Since I already had 2 30 foot long cables, I cut off 4 or 5 foot off each cable. That way I had a 25 foot long + cable and a 25 foot long - cable to connect into the combiner box. I spliced about 20 foot of cable between the 2 short 4 foot long pieces of + and - short cable to make the complete circuit between the panels on each rack. Both the short pieces were connected to the panels. So when I spliced the wire between the + of one panel to the one with - that made the circuit between the 2 panels in series. and why I got shocked. Good thing I didn,t have all the panels connected to make the series string or I would have got shocked with 16 185 watt panels. I know not to do that agin!!! :D solarvic:D
  • inetdoginetdog Solar Expert Posts: 3,121 ✭✭✭✭
    Re: Shocking question
    ggunn wrote: »
    Well, obviously there was a completed circuit somewhere. It's possible that the other cut end was making contact with the racking and you completed the circuit by touching the rack at the same time as the end you were working on. I'm glad you're OK.

    That is one of the reasons that most panels come pre-assembled with MC4 connectors, since those do not expose a bare contact on either wire. When you use a cut-off MC4 extension cable to connect to a terminal block, the terminal connection must be made before the panel connection.
    Also another reason to cover the panels just in case. (And to use a safety harness when working on a pitched roof!)

    Note that the OP did not report getting shocked, just reading a voltage, so it it not clear whether there would have been enough current available to actually shock him.
    Yet another reminder that pv panels are a current source and not a voltage source, in terms of their dependence on light input.
    SMA SB 3000, old BP panels.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Shocking question
    inetdog wrote: »

    Note that the OP did not report getting shocked, just reading a voltage, so it it not clear whether there would have been enough current available to actually shock him.
    Yet another reminder that pv panels are a current source and not a voltage source, in terms of their dependence on light input.
    Not to be argumentative, but this is from post #1: "While wireing 1 string of panels into my combiner box from 2 separate top of pole mounts I got shocked."
  • inetdoginetdog Solar Expert Posts: 3,121 ✭✭✭✭
    Re: Shocking question
    ggunn wrote: »
    Not to be argumentative, but this is from post #1: "While wireing 1 string of panels into my combiner box from 2 separate top of pole mounts I got shocked."

    Touche. I was referring to the post by tmarch and not the one by the OP (that was lost back on an earlier page) :-)

    The OP did not cover his panels.
    SMA SB 3000, old BP panels.
  • mikeomikeo Solar Expert Posts: 385 ✭✭✭
    Re: Shocking question

    A little poem from my teenage days working with old radios in the 50's

    Timothy Twerp was most astounded,
    When what he thought was-WASN'T grounded.
    In fact, one could say, he was really transfixed
    With his thumb on pin 3 of a live 6L6.
  • inetdoginetdog Solar Expert Posts: 3,121 ✭✭✭✭
    Re: Shocking question
    mikeo wrote: »
    A little poem from my teenage days working with old radios in the 50's

    Timothy Twerp was most astounded,
    When what he thought was-WASN'T grounded.
    In fact, one could say, he was really transfixed
    With his thumb on pin 3 of a live 6L6.


    6L6, ain't that some kind of "tube" whatchamacallit? :-)

    The old electrician's (and radio tech's) rule of keeping one hand in your pocket when dealing with live systems seems to apply here, but it also has to be qualified with language about not kneeling on a metal roof while wearing shorts unless you keep both hands in your pockets. :-)
    SMA SB 3000, old BP panels.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Shocking question
    mikeo wrote: »
    A little poem from my teenage days working with old radios in the 50's

    Timothy Twerp was most astounded,
    When what he thought was-WASN'T grounded.
    In fact, one could say, he was really transfixed
    With his thumb on pin 3 of a live 6L6.

    Hahahaha LOVE you're little poem Mikeo :D
    Has special meaning for me. Memories. I must be getting old. :D
    Some of my most memorable experiences were the result of personal contact with the 450VDC "B+" in Grundig reel to reel tape recorders. lol
    Why the heck did Grundig use voltages that high? I suspect for the same reason a dog licks his ***, because they could!
  • CDN_VTCDN_VT Solar Expert Posts: 491 ✭✭✭
    Re: Shocking question

    Here one MUST watch DC shocks over AC type.
    Yearssssssss ago I did time with Hydro Power Authority ,Now BC Hydro , Line, transformer, substation ,and generation work, AC stuff , hot gloves /sticks all that goop.. Made a switch to Vancouver and into the Bus Division known as trolleys . 600vDC power and ground wires overhead.. This is on the WET COAST of Canada..

    Now they have these sensing strips that come from the ground and touch the underside of the coach / Bus. There found in the BUS YARD and in selective turn-a-rounds where Vehicles won't drive over them. They will detect if the coach has an internal leak to the body , making the Coach HOT .

    Called Hot Coach !!
    Now the funny stuff that folks don't realize is the entrance and exit doors are isolated from the coach body , fibreglass poles/handrails with nylon bolts ETC. steps that are wooden mounted with rubber isolation.

    In the bus shop there on all of the pit stair access areas and in the pit itself were wooden bats. They were to free someone who got stuck while touching a hot coach and grounding through them. You had to smack an arm or some part to get them to release. AC kicks and POW your jolted off , DC your stuck till someone breaks the connection and man is it painful on your muscles. I have felt AC tingles , hair raising Elmos fire in a sub station , But the DC jolt I got on a Hot tether was the worst.
    Was a DUH moment on my part.. Always pull the Ground tether / pole off first..

    Dem were the years when cooties was the worst you could catch.


    DC shocks are very painful. Glad everyone posting here is above the dirt ;) .

    Proper attire , shoes / pants / etc should be worn also , I have a red neck , but glow in the dark , still ;) .

    VT
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Shocking question

    Great post CDN_VT. Interesting read, good information :)
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Shocking question
    mikeo wrote: »
    A little poem from my teenage days working with old radios in the 50's

    Timothy Twerp was most astounded,
    When what he thought was-WASN'T grounded.
    In fact, one could say, he was really transfixed
    With his thumb on pin 3 of a live 6L6.

    My residence in Geezerdom notwithstanding, I loves me some 6L6's! Also 6V6's and EL34's. I have 6L6's in my Super Reverb and Mesa Boogie, 6V6's in my Deluxe Reverb, and EL34's in my Marshall. Don't try to hand me no solid state amp! :D
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