Re: Is it safe to use computer during lightning/thunder storm?

From: w_tom (w_tom1_at_hotmail.com)
Date: 09/24/04

  • Next message: Ron Reaugh: "Re: Is it safe to use computer during lightning/thunder storm?" 
    Date: Thu, 23 Sep 2004 21:44:03 -0400

      In order to confuse issues, some will hype nonsense about
    airplanes and then post insults as proof of his superiority.
    We are discussing a particular type of surge where a cloud
    conducts to earth. That is completely different from
    transients that transverse airplanes. Others have had this
    explained to them previously. To subvert the discussion, they
    insult and then throw in totally irrelevant topics such as
    airplanes.

       Once ionization takes place, then capacitance of both sky
    (air) and earth becomes irrelevant. One of the best
    capacitors is air. However air gets converted into a good
    conductor (plasma) due to something called breakdown voltage.
    We require protection and only discuss surges after ionization
    has occurred. Surge current (not surge voltage) becomes the
    dominant variable after breakdown voltage is exceeded.
    Capacitance is made irrelevant.

      Surge protection is about earthing an ideal current source.
    A surge is a current source after ionization has occurred.
    Voltage will rise only as necessary to maintain that current.
    This is the point when damage can occur and when protectors
    must shunt that current to earth. Concepts that apply both to
    properly earthed 'whole house' protectors AND to properly
    earth Franklin air terminals (lightning rods). They both do
    the same thing. Divert the surge current to earth ground so
    that the surge will not find destructive paths through
    household electronics or church steeples.

    Suraj Singh wrote:
    > Surprised to see that no body talked about the capacitance of the
    > earth in this discussion.
    >
    > Lightening do not bother to hit the airplane. Even if it does it do
    > not damage anything. Airplane capacitance is too small so a very
    > minute flow of charge can change its potential to match the cloud
    > potential. flow of minute change means little current ( micro amp)
    > which wont damage anything.
    >
    > Imagine a situation where the plane has just taken off the ground,
    > lightening strikes its body and discharge to the earth through bottom
    > including pointed antennas in the wings; you can imagine the damage to
    > the circuit from where the antenna is connected.
    >
    > As per the lightening is concerned one can not ignore earth if you are
    > close to it. You can dare to ignore if you are a much bigger mass
    > than earth.
    >
    > You can raise the common mode potential of the system (say PC and
    > Modem), it helps but up to what extent? The charge on it will seek the
    > earth and if a short and quick high conducting path in not provided,
    > it may break down the air gap and discharge to the nearest path to
    > earth through the mouse wire.
    >
    > Concept of GPR will provide much better protection if the whole house
    > is considered as a sub system. It will be economical too.
    > Power strips provide protection but for small surges only.
    >
    > Best regards,
    > Suraj

  • Next message: Ron Reaugh: "Re: Is it safe to use computer during lightning/thunder storm?"

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