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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