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Never! Never assume a circuit is dead!

  1. Jan 3, 2008 #1
    Just wanted to post to the other electrical people how it can get you even if you have all of the bases covered, in your thinking. I have worked with all kinds of high power equipment and low power equipment since 1970. Last night I had a 480VAC three phase circuit locked out (locked out for two weeks) that I was working on just the night before but someone powered it up from a separate supply on another shift. I have been hit many times in my career but never like that. Once it got me I couldn't let go and I was alone. The odd thing is that I was thinking rationaly during the process and thought to drop to my knees and kick away. After several attempts I was able to do this with a bleeding mouth, a numb tongue and ringing ears, along with arc burns on my hands. The largest being one inch long, a quarter inch wide and a sixteenth of an inch deep. I hope it leaves a permanent scar that will keep reminding me. I kept quiet because it was my personal friend that made the mistake but wanted everyone to know to NEVER ASSUME A CIRCUIT IS DEAD EVEN WHEN YOU KNOW IT SHOULD BE. Thanks, got it off my chest. Robert
     
  2. jcsd
  3. Jan 3, 2008 #2
    Glad to hear that you're around to tell the tale. A severe electric shock is a horrific experience.
     
  4. Jan 3, 2008 #3
    After surviving I found it quite pleasureable. When you get bucked off of the horse, you either ride it or the animal is sent to the glue factory. After the experience I am quite elated because I know how close I came yet survived.
     
    Last edited: Jan 3, 2008
  5. Jan 3, 2008 #4

    stewartcs

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    Good to know you made it, you're very lucky.

    I would suggest that your company revisit their lock-out/tag-out program to ensure the proper checks are performed to ensure the system is indeed isolated.

    I remember back when I was in the Navy there was an extensive procedure on how to lock-out equipment that included more than one person verifying it to be correct and signing off on it. It seemed to work very well.
     
  6. Jan 3, 2008 #5
    Mr. Stewart you are 100% right. We have a lock out policy and the power source was locked out. Somebody rigged it at a remote location for a stupid reason. All is forgiven and I celebrate life but want everybody to know to watch their P's and Q's because nobody else will and will cheat the system. It was my fault because that was the first thing I learned in Fire Control School "A", always measure a dead circuit with a good voltmeter before putting your hands on it.
     
    Last edited: Jan 3, 2008
  7. Jan 3, 2008 #6

    stewartcs

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    That someone should be made very aware of how stupid their action was - friend or not. Quite often people forget that these systems are in place for a very good reason and should not be circumvented for any reason.

    Personal verification of a de-energized circuit is a must (I learned that in the Navy too) as you already know. Honestly though, if I had been working on it for two weeks, I probably wouldn't have re-checked either.

    I guess the point now would be to ensure all technicians have a refresher course in lock-out/tag-out to emphasis the importance of it.
     
  8. Jan 3, 2008 #7
    Mr. Stewart, to be honest with you it was not a underpaid technician but a overpaid electrician. Here is how they did it: The control circuit of a 700HP induction motor was remotely energized even though the main power was locked out. When the control circuit was remotely powered from a extension cord plugged into the wall, this also powered up the main control transformer that is fused at 30A on the secondary side. This produced 480VAC on the primary even though the main circuit breaker was locked out. The transformer works both directions and that surprized some people when I tried to explain it. I got hit with 480VAC from a lowly control transformer (have not checked but guessing 30,000KVA) that was powered up in the wrong direction and when I went to work on the line side of the soft start it got my attention. A large control transformer is needed because it also energizes some heaters in the oil tank of an ammonia compressor. A refrigeration "technician" told the first shift electrican to power up the heaters even though the circuit is locked out. The stupidity comes into play because the heaters are not needed at this time because the soft start is broken and you only need the compressor oil to be warm when starting a working system.
     
    Last edited: Jan 3, 2008
  9. Jan 3, 2008 #8
    did you bite yourself?
     
  10. Jan 3, 2008 #9

    mgb_phys

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    Glad you're OK - that's why I only work with CMOS!
    A guy in the welding shop once taught me always to check if something is hot with the BACK of your hand, then if it is you don't get a grab reflex.
     
  11. Jan 3, 2008 #10
    how about testing with a voltmeter? :P
     
  12. Jan 3, 2008 #11

    DaveC426913

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    How about shorting it with a screwdriver?
     
  13. Jan 3, 2008 #12

    dlgoff

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    It's really good you posting this here. I'm sure this mistake has been made before with a much worse outcome. I hope everyone here will take a look at this.

    I worked with a guy that had a 115v cheater cord (alligator clips on hot and neutral) for his bench. Yep, he picked up clips; one in each hand. He got similar burns and became unhooked after falling off his bench chair. So it doesn't take 480 volts to kill you.

    I got nailed once just by megging a motor.

    Regards
     
  14. Jan 4, 2008 #13

    mgb_phys

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    Sorry - I meant thermal hot.
    I would probably still briefly touch an electrical connection with the back of a finger, with the other hand safely in my pocket and wearing insulating shoes, before grabbing it with my hand.
    The trouble with a voltmeter test is that you have to be sure the VM is working, is on the correct scale, test AC and DC and be sure that whatever you connect the -ve to is connected to the same earth potential you are.
    Neon tester screwdrivers are probably better than a VM for this.

    Perhaps there is a market for some electro-flurescent material that would glow in a electrical field - it could be made into an EEng nail varnish, so your finger tips would light up before you touched a live wire.
     
  15. Jan 5, 2008 #14
    David90, how did you know that? I was bleeding from the mouth because I was biting my tongue but that was the least of my problems. My ears usually ring a a low decibell but they went up 10db, were really ringing, sounded like a fire alarm. I should also mention they have now stopped ringing when they used to ring all the time before. I will write the AMA and suggest this as a cure for tenititis, cant spell it but that means ear ringing.

    The taste buds have returned, the ear ringing has stopped, the arc burns were caurterzed, and I have forgotten it.

    You must be strong under any circumstance. Fight as long as you can.
     
    Last edited: Jan 5, 2008
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