[NTLUG:Discuss] lightning - was "lightening"

[terry]

Fred wrote:

>Lightning - el Zappo - something I know something about 
>lightening - shedding weight - something that escapes me
>
>Direct hits on homes are rare, but they do happen. One in the Dallas area last
>week... big fire, total loss....  but the biggest worry is the zaps to power,
>telephone and cable lines that run overhead. These blasts can, and often do,
>damage any electronic equipment connected to them. A friend would shut down his
>system and pull the plug from the wall anytime that lightning was in the area,
>but he forgot about the phone line. ZAP! Destroyed the modem, of course, AND
>fried the MB.
>
>High voltage, fast rise time pulses can see "grounds" as high impedance
>inductors and take an alternate route to the real ground. Grounding is good, it
>just may not perform during a lightning hit like you want it to. - note - to
>fully understand it, you gotta really know analog - like what happens when a
>current of God-awful proportion causes an inducted current to flow in a
>seemingly totally isolated conductor. It doesn't have to be but a tiny fraction
>of the original crack of doom to destroy equipment. 
>
>Good, low impedance ground paths, pulse suppression devices, an adequate UPS
>and an understanding of UHF signal propagation in wiring will go a long way
>toward keeping you and your equipment safe during stormy weather.
>
>Fred
>
>  
>
 When thousands of volts are injected into power or phone lines, almost 
anything in line will fry or die (regardless of protective devices). 
 Your only hope is that insurance will cover it.  Often times, [and many 
don't realize this], your typical home owner's insurance will cover 
these loses.

A side note:  If you'll notice [in many regions] (some) gov. or military 
buildings have a series of lightning rods connected  in series to heavy 
gauge wiring that goes along the roof lines and terminates into multiple 
subterranean grounding devices.

Another note:  I wish I had pictures, but have a friend/customer that 
had her house pretty much destroyed, (in Snug Harbor on Eagle Mt. Lake), 
by a lightning strike that hit the power feed line.  It burned ALL  the 
electric wiring, literally blew up the breaker panel.  Not only that, 
but all the electrical devices and appliances were fried, some almost 
beyond recognition.  There were burn marks on all the sheet rock walls 
up and down and horizontally from outlet to outlet, from switch to 
fixture.  The insurance company fixed it all but it required completely 
gutting the house, replacing all sheet rock, wiring etc.  After it was 
all done, it cost more to repair damages, that in would have to bulldoze 
the house and build it anew.

I have a couple of transceivers connected to outside antennas and used 
to unplug coaxes from them, (as well as turning off/unplugging 
computers) during thunder storms.  After seeing electrical arcs from 
coax connector to chassis spanning 4 and 5 inches, I began cramming the 
coaxes into a large glass jar. (And this was just from cloud to ground 
strikes near-by.)  ...  I no longer unplug anything. I've come to the 
conclusion that it's easier to do nothing. ( My life is a bit more 
valuable than any electrical device.  )   :)

As far as computers are concerned, I guess it's just yet another 
incentive to back up your data to an external media device.  The only 
safe computer is one that's not connected to anything.  Disconnecting a 
computer from everything prior to, or during a storm is impractical and 
a hit-and-miss process at best. For one, you're not always there.  For 
two, you're not always aware of the eminent danger.

 All the protective devices you can get may help to defuse small amounts 
of current, but they all have limits way below the magnitude of the 
thousands of volts of electricity that may enter wiring in the event of 
a strike that hits power or phone lines near your house.  ( .. and it 
happens a lot in this area/region. )


-- 
Registered Linux User #188099
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