[NTLUG:Discuss] lightning - was "lightening"

[terry]

terry wrote:

> 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. )
>
>
(Before you say it, I will): I suppose my response was a bit off topic. 
 It may be good info/advise for home owners, but for you guys that have 
servers you're trying to protect, I guess you need all the protective 
devices you can afford to employ.  (Expect the worst and hope for the best.)


-- 
Registered Linux User #188099
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