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Re: [Electronics_101] Re: Safety question about current...

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  • Stefan Trethan
    On Sun, 02 Jul 2006 08:32:50 +0200, Bob Hyland-PMP ... I second that opinion and will add the suggestion of using an isolation transformer instead. Sometimes
    Message 1 of 71 , Jul 2, 2006
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      On Sun, 02 Jul 2006 08:32:50 +0200, Bob Hyland-PMP
      <BobHyland@...> wrote:

      >
      > Um Jack... help me out here. You shun the power outlet, but you
      > create one by using a 300W power inverter? How is this "safer"? You
      > are still looking at 120V @ 300 Watts. I would assume that using a
      > standard GFI outlet would give you better safety than using this
      > home-brewed option. That is, unless there are additional safety
      > mechanisms built-in along the way that I don't know about.
      > Also, 300 Watts is a lot of power to be delivered by batteries. Just
      > how many are you using to power this thing, keeping in mind the
      > eficiencies of each component along the trail?
      > As an alternative, you could just use a standard 12V power supply
      > that connects to the mains, and plug in the inverter to that! Seems
      > like it would give you the same "safety" and you would not have to
      > keep replacing / recharging the batteries....
      > Bob H.


      I second that opinion and will add the suggestion of using an isolation
      transformer instead.

      Sometimes GFI protection is better, sometimes isolation.
      Basically if you are somewhat grounded (feet, chassis, etc) a GFI will
      protect you and switch the power off if you touch the hot side. You would
      still feel a zap though. If you use a GFI make damn sure it is 30mA fault
      current or less. I was trapped once on a GFI protected circuit with an old
      200mA GFI that did not trip. You wouldn't believe you can pull out the
      plug of a power strip lying on the floor with your feet, but you can if
      you have no use of your hands! (Note to self: Next time just walk/jump
      back until the connection is pulled away you stupid idiot!).

      Anyway, an isolation transformer in comparision will not do anything if
      you touch hot and earth, no current flowing. No zap, but no power-off
      either so it makes sense to add either an isolation monitor or test
      everything you repair after an isolation transformer with an isolation
      tester for ground faults.


      Now that was the hot/ground fault. What if you touch hot AND neutral? Well
      - DON'T!
      If you have a GFI you might be grounded, and it would have tripped as soon
      as you touched the hot wire. But if you got in this situation to touch
      both you are probably not grounded. An isolation transformer wouldn't help
      either.
      So this is one mistake you need to avoid.
      The isolation transformer can save you from one mistake - but you mustn't
      ever rely on it because that'll let you make the second mistake. For
      example if there is a ground fault in the unit and one mains wire is
      shorted to the chassis - and you do not know about this - the one single
      fault the isolation transformer can forgive is USED UP!.

      ST
    • Roy J. Tellason
      ... For me as well. :-) ... Interesting, as I d never heard any of that. But as you say OT. :-) -- Member of the toughest, meanest, deadliest, most
      Message 71 of 71 , Jul 4, 2006
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        On Tuesday 04 July 2006 04:01 pm, Jack Giammerse,Jr. wrote:
        > Thanks,Roy,
        > I have heard the phrase Sealed Lead-Acid before,but do not remember
        > seeing the acronym SLA until here in this thread.Here in the U.S.,the
        > acronym SLA only brings to mind the "Symbionese Liberation Army",

        For me as well. :-)

        > The lady did get out of prison after several years and go on to live a more
        > normal life,and she did all this with her dignity intact. I admire her
        > greatly for that,because it is a testament to her true character.

        Interesting, as I'd never heard any of that. But as you say OT. :-)

        --
        Member of the toughest, meanest, deadliest, most unrelenting -- and
        ablest -- form of life in this section of space, a critter that can
        be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
        -
        Information is more dangerous than cannon to a society ruled by lies. --James
        M Dakin
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