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

Discussion in 'Electronic Basics' started by nospam256K, Sep 21, 2004.

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  1. Suraj Singh

    Suraj Singh Guest

    Ron,
    we all understand his simple point.
    see between the lines.


    What do you think up to what potential you can bring this sub system with
    reference to the earth?
    It may break the air dielectric from any point of the subsystem.

    I too understand the theory and looks good theoratically. Unfortunately
    real lightening hit do not follow these.
    It do not follow ohms law either. air around just get ionised.

    The first thing is to keep the same potential for all connection of the
    subsystem.

    this helps but this is not enough

    Second point is, do not let the potential of subsystem (with respect to its
    surrounding) rise/fall too much.

    So providing a farady cage adds to the protection.


    Suraj
     
  2. Suraj Singh

    Suraj Singh Guest

  3. w_tom

    w_tom Guest

    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.
     
  4. Ron Reaugh

    Ron Reaugh Guest

    w_tom == Suraj Singh

    Check the headers
     
  5. Suraj Singh

    Suraj Singh Guest

    Perhaps you do not understand the relationship between thunder bolt
    and Earth.
    Lightening always searches a better path to the earth through a
    conductor and do not spare a non-conductor either if it needs.

    Study up and try to understand this simple point.

    Why the lightening is so hungry to get in to the earth?? Its the
    capacitance of the earth.

    The capacitance of the Earth is very, very large indeed. This means
    that transferring charges to it will not significantly change its
    potential, any more than pouring jugs of water into the sea will
    significantly change sea level. So in the same way that we measure
    heights and depths from sea level so we measure potential from that of
    the Earth. We say that the Earth is at zero potential. The potential
    of an object is the potential difference between it and the Earth.

    The capacitance of a normal adult is about 160 pF. This means if we
    walk along a nylon carpet and pick up a static charge of a millionth
    of a coulomb we shall be at a potential of more than 6000 V! If we
    then touch (about to touch) something earthed such as a metal door
    handle we may feel a slight shock, but the charge transferred to Earth
    is so tiny that it will do us no harm at all.

    To protect CMOS chips from ESD we also connect a wrist starp to the
    chesis and do not bother to connect the whole thing to earth. but
    remember that lightening is not a tiny charge.

    Read the last para of the following practical experience; see how the
    increased protection was provided by a faraday cage.

    http://web.ukonline.co.uk/freshwater/lightng.htm


    Suraj
     
  6. Suraj Singh

    Suraj Singh Guest

    Please stop writing abusive replies.

    Checking the headers are your job. All others are here for helthy
    technical discussion.
     
  7. Bob Ward

    Bob Ward Guest

    http://www.physlink.com/Education/AskExperts/ae568.cfm
    Question

    How is a plane protected from Lightning strikes?

    Asked by: Sridhar Narayanan

    Answer

    Since the outer skin of most airplanes is primarily aluminum, which is
    a very good conductor of electricity; the secret to safe lightning
    hits is to allow the current to flow through the skin from the point
    of impact to some other point without interruption or diversion to the
    interior of the aircraft.
    Estimates show that each commercial airliner averages one lighting hit
    per year but the last crash that was attributed to lightning was in
    1967 when the fuel tank exploded, causing the plane to crash.
    Generally, the first contact with lightning is at an extremity...the
    nose or a wingtip. As the plane continues to fly through the areas of
    opposite charges, the lightning transits through the aircraft skin and
    exits through another extremity point, frequently the tail (as shown
    by Gauss's Law).
     
  8. Kent Wills

    Kent Wills Guest

    I was just walking down the street, when someone handed me a piece of
    paper. I thought it was something for a free meal at Popeye's
    Chicken. Instead, I found that on Thu, 23 Sep 2004 02:16:01 GMT, "Ron
    You'd most likely be safe having that party, but it's gonna suck
    big time if your machine fries.

    Kent
     
  9. Kent Wills

    Kent Wills Guest

    I was just walking down the street, when someone handed me a piece of
    paper. I thought it was something for a free meal at Popeye's
    Chicken. Instead, I found that on 23 Sep 2004 16:12:57 -0700,
    Well, the OP did only ask about computers.
    Actually, airplanes do get hit. Probably more than most people
    realize, although I don't have any actual cites to offer.
    Kiss that antenna good bye. It's toast.
    Eh? If you had a much bigger mass than the earth, you couldn't
    possibly be ON the earth. You couldn't possibly fit.
    Which is why I think everyone should invest in a wireless optical
    mouse :)
    No they don't, actually. Power strips are nothing more than
    additional outlets. Surge Protection strips can add a degree of
    protection. These are two different things. Always keep that in
    mind.

    Kent
     
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