Floating voltage vs ground voltage.

Discussion in 'General Electronics Chat' started by coinmaster, Jun 16, 2016.

  1. coinmaster

    Thread Starter Member

    Dec 24, 2015
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    I have noticed that every time I measure a floating voltage relative to ground with a multimeter it always shows milivolts.
    I thought voltages were all relative to eachother so even a floating voltage would still have a relative potential to earth.
    Yet it always seems to show near 0 potential no matter what the floating voltage is.

    What's the reason behind this? If you float lethal voltages are they no longer lethal relative to earth?
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    If it is truly floating it will have no earth ground reference.
     
  3. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    The meter does not have infinite resistance across its leads, therefore, your "floating" circuit is no longer floating. It is grounded through the multimeter.

    Regarding lethal voltages: technically (theoretically) yes, if there is absolutely no return path there is no circuit for lethal currents to flow. But, I wouldn't test it with my body.
     
  4. coinmaster

    Thread Starter Member

    Dec 24, 2015
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    Hmmmm. So if I had the output of an amplifier floating at high voltages would it be safe to wear headphones through this amplifier? I occasionally read about people using electrostatic headphones connected directly to the HV source and they say that it is scary to do so.
    I'm not sure how this applies to floating voltages since it supposedly cannot hurt you?

    How is floating voltage immune to the potential of every other voltage in the world?
    I thought voltage potential was about an excess or absence of electrons? Surely this means even a floating voltage has a relative potential to ground that is not always zero?
     
  5. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    I know nothing about HV electrostatic speakers, so, no comment.

    Current kills, not voltage. To establish flow of current, a closed loop is required. No current can flow between two objects completely isolated from each other.

    With that said, isolation is a tricky thing. Things that appear to be isolated may not be. Things that were isolated a short time ago may no longer be isolated now. Many electrical products of long ago depended upon isolation to avoid electrical hazards. Many people died.
     
  6. coinmaster

    Thread Starter Member

    Dec 24, 2015
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    An isolation transformer and chassis ground would create a completely isolated system right?
     
  7. joeyd999

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    That's a good part of it. There are other criteria -- here are some buzz words you can Google: creepage, clearance, dielectic strength, pollution degree, and others.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    In order to have a voltage to earth something, which is grounded to earth, has to establish that voltage.
    It the circuit is completely floating then there is nothing to generate a voltage to earth.
    But if once side of a floating high voltage supply accidentally gets connected to earth, then you can get zapped. :eek:

    Certainly a floating supply can have a static charge relative to earth but the worst that static charge will do is give you a momentary shock, like walking across a rug with low air humidity and touching a grounded surface.
     
  9. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    Voltage potential is usually from the separation of charge in a circuit were the total number of charges remain the same. A small 9 volt battery inside a transistor radio is seen as an object with a neutral charge to ground if both terminals are floating. The electric field of the battery is generated from charge separation in the electro-chemical cells.
     
    Last edited: Jun 17, 2016
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