I have always assumed lightning came down but reading
here suggests that it might be the other way. Anyone
care to be definitive?
--- Marty Michener <> wrote:
> At 04:39 PM 7/10/02 -0400, Walt wrote:
> >My theory is that the power surge that came in was
> riding on only one
> >leg of the power. And the SCSI card got caught in
> the middle and that
> >was how it all got into my computer. Also caught in
> the middle was the
> >ethernet lan. My computer lost the transmit side of
> it's ethernet, the
> >others lost the receive. It's not clear if the
> phone line surge was
> >internal to the house from this difference, or a
> separate surge that
> >came in from outside via the phone line. It's only
> damage was fried
> >suppressers.
>
> Walt - what a terrible time you have been having -
> my hopes for speedy
> resolution go out to you and the troubled lan. It
> makes you wonder when
> you read about Electro-Magnetic Pulse terrorism, if
> it ain't already here. ;=D
>
> I want to make a point about the weird combination
> of factors involved in
> lightening. I made quite a study of it many years
> ago, since the effects
> sometimes seem quite bizarre and hard to understand.
> I was constructing a
> fifty foot pipe tower for anchoring one end of my 40
> meter ham antenna ca.
> 1955, and was required to understand a lot about
> lightening by my father as
> a pre-requisite. I would NOT say I am an expert,
> only that I am more and
> more amazed as I continue to learn. I guess we all
> need Faraday shields
> for homes these days.
>
> There are effects that can be labelled mainly
> capacitative - voltage peaks
> across insulators, effectively, and those that can
> be considered inductive
> - magnetic fields inducing currents in parallel
> inductor systems, caused by
> the very rapid change in current (di/dt). These
> induced effects are the
> most poorly appreciated by most of us, since they
> occur in seemingly
> disconnected systems. The rate of change in
> current, di/dt is one of the
> most spectacular facts of ordinary lightening - the
> process happens so fast
> that two turns of a wire loop can become a huge
> inductive mass, and the
> voltage across such a coil become so high as to make
> the current jump as a
> spark through the air, rather than "take the time"
> to pass through the
> small two turn coil. Many arrestors work by
> allowing a short gap shunt to
> direct ground.
>
> Of course they tell you lightening travels from the
> ground up into the sky,
> not the reverse the way is popularly assumed. I'm
> not sure there even IS a
> difference, here, but ok. ;^)
>
> But that is the easy stuff. Induced amps in
> parallel conductors is the
> hard one. I have seen, here in Hollis, a plumbing
> system, dredged
> postmortem from a well, where the iron pipe was so
> twisted it was almost
> tied in knots by the force of a nearby bolt. As
> nearly as we could tell,
> the lightening current started concentrating in the
> deep bedrock aquifer,
> travelled up the well casing thence to the pipe
> toward the house, jumped
> somewhere in the yard to an oak root, travelled up
> the chestnut oak,
> bursting it from the heat and steam (covering one
> side of the house with
> its bark and wood fibres as if it had been
> spray-painted onto the siding)
> and emerged from the leafy top to appear as a bolt
> in the sky. Needless to
> say, the well-submersible pump was fried, and it all
> required re-wiring
> from the basement to the well. The house, except
> for the pulp-blasted
> exterior, was spared in this case. No computers
> around to test, but lots of
> blown circuit breakers.
>
> So I have come to look, in cases of near bolts, for
> indications of ground
> potential itself having been shifted radically. And
> this is the way I
> would surmise your two-leg problem. The problem
> with saying the bolt came
> in primarily on one leg is that lightening energy is
> so rapid it will
> hardly go around any corners, like ordinary house
> wiring, because of the
> high inductive impedance at that high a frequency of
> a simple "U" in the
> wire. I think we need those ferrite anti-rf blocks
> around all wire and
> cable leads entering our domains. You can assume
> the "ground" itself moved
> toward one leg and away from the other leg, or that
> the two ground
> locations became momentarily separated by many, many
> volts. I also suggest
> that the surge that killed the lan was induced,
> rather than conducted, but
> this would be hard to do physically if it is either
> twisted pair or coax.
>
> I am afraid I have more questions than suggestions,
> but, really, Walt, as
> in all things, I do marvel at your patience.
>
> my very best,
>
> Marty Michener
> MIST Software Associates
> PO Box 269, Hollis, NH 03049
>
>
> coming soon : EnjoyBirds, bird identification
> software for all AOU area.
>
>
>
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