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Re: [TCML] Extremely LARGE spark. 2
gary350@xxxxxxxxxxxxx wrote:
I grew up on a farm in the planes states everyone had lightning rods
on their house and barn. The cable from the roof to ground was a
5/8" diameter braided wire. It looked like about 10 wires each wire
about 1/16" diameter braided into a hollow tube shape. Lightning
rods were spaced about 10 ft apart on the roof. The cable ran right
down the center of the roof and down both ends of the house attached
to a ground rod on each end of the house. Faraday cage is what makes
it work. The barn also had the same lightning rods setup. I
remember seeing lightning strike the barn once the cables light up
like a white laser bean for a split second. After the storm had
passed I ran to the barn expecting the cables to be melted or
something but they looked fine no different then before the storm.
The weathered copper was still green looking like before.
I think 1/2" copper plumber tubing will work for lightning rods and
cable grounds. I am going to put copper tubing on my roof with a T
fitting every 10 ft. I will mount the T straight up with a 3 ft
section of copper tubing sticking straight up from each T. The 3 ft
pieces will be my lightning rods. I can run the copper tubing down
the side of the house to an earth ground.
Hi Gary,
I'm sorry to hear your house got hit, but thankfully nobody was injured
and your house survived. Many years ago, what was apparently a single
"super" bolt of positive lightning hit a house about a block away from
ours. It sounded like a bomb going off, with echoes of heavy rumbling
thunder lasting for at least 15 seconds afterwards. The occupants were
away on a weekend trip at the time, and the bolt apparently ignited
numerous simultaneous fires inside the house. The house was fully
engulfed by the time the firefighters got there, and it burned to the
ground.
Re: your proposed lightning protection system:
When passing high currents (10's - 100's of kA), thin hollow conductors
can collapse from magnetic forces. An example of this effect due to an
estimated 80+ kA current from a positive lightning strike can be seen in
the following report. The strike apparently passed through the metal
aileron control hardware of a glider, causing the glider to partially
disintegrate and crash. Fortunately the pilot and student both had
parachutes and survived. Of interest during an analysis of the wreckage
was a 16 mm diam x 1 mm thick aluminum tube that was crushed from the
magnetic fields associated with the lightning current (figures 8c-8e):
http://tinyurl.com/3wpjab (pictures)
http://tinyurl.com/2fymlb (entire report)
Thick wall (K) "hard" copper tubing will be significantly more resistant
to collapse than soft copper tube or thinner (M or L) pipe. However, you
may want to reconsider using a "roll your own" lightning protection
system, even though it may work in theory and practice. You will likely
be violating state and local building codes if your equipment or
installation technique do not comply with National Fire Protection
Association (NFPA 780) standards. The practical impact is that your home
owner's insurance company may refuse to cover ANY future
lightning-related damage, effectively leaving you uninsured against
future events.
Bert
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