So I read this thread with great anticipation of seeing how it relates to
the subject of this newsgroup! Let's all collectively compliment all these
snooty astro-phycists on their deep knowledge and ask them to go back into
their laboratory so that we can continue to enjoy our hobby!

Just my 2 cents.

--
_______________________________________
"The difference between 'involvement' and 'commitment' is
like an eggs-and-ham breakfast:
The chicken was 'involved' - the pig was 'committed'."

http://community.webshots.com/user/godwino

"Dave Bell" wrote in message
...
On Sun, 27 Jul 2003, w_tom wrote:

Let's review where all that energy was applied and how much
- with numbers so that we don't do what junk scientists must
do.

Don Kelly in Newsgroup sci.physics.electromag on 4 Nov 2000
entitled "Oddball question":
over the duration of the storm (and a wide area) ... A typical
stroke will reach its peak in about 1-2 microseconds and die to
about half peak in 50-100 microseconds. Millionths of seconds,
not seconds! There may be several strokes in the same path but
even 3-5 strokes will take less than 1/1000 second. The strokes
just appear to last seconds.
Yes there is a high peak power in a stroke but this does not
translate into appreciable energy (about 55 KWH (200MJ)for an
average stroke). Energy is what we need, not high peak power.

Which, for "Gee Whiz!" value, works out to on the order of 2x10^12 Watts
over 100 uS...

The US Army defines in TM5-690 a wire size sufficient to
discharge lightning without damage. 10 AWG. This makes
complete sense once one learns a direct lightning strike has
so little energy.

Various non commercial websites suggest that a typical lightning
strike releases 250 KWH of energy. A big one may release 10 times
that
much. That is a lot of energy. Admittedly, most of that is
dissipated in the air
above where it strikes, but I think it is disingenuous to
characterize it
as "little".

A lightning rod above the pond and properly earthed by 10
AWG or heavier wire is more than sufficient to intercept and
divert lightning to earth without pond damage.

Most lightning rod manufacturers use 2 or 0 gauge wire as the down
wire.
10 gauge seems to me a little flimsy. Given that a 10 gauge copper
wire has a
resistance of about 1 ohm per 1000 feet, and given a total length
of wire
of about 50 feet, we are dealing with 0.05 ohms of resistance.
Given also
that an average lightning strike can have a current of 10,000 amps
(NASA
has measured at least one strike of 100,000 amps)(and that the
conductor takes
the entire current) we are dealing with a dissipated power of
10000^2*.05
or 5 million watts. Or 100,000 watts per foot of wire. Admittedly
this is
for a very short time. But I submit that 100000 watts applied to a
foot of
this wire over a millisecond will melt or otherwise seriously damage
that
wire.

In addition to the DC resistance, you need to take into account the
inductance of the grounding wire. In the far more limited world of
industrial high energy discharges, an associate observed multiple
instances where a large laser flashlamp power supply was dumped to the
solid copper lab grounding grid. The cable from the crowbar switch to the
grid was about 4 feet long, running perhaps 30 degrees off the vertical.
They would see sparks "shortcut" from 18 inches or more up the cable, to
the floor, rather than continue down the direct path. What's the dry air
breakdown voltage for 18 inches? These *potentials*, with significant
energy behind them, do occur, even with properly grounded equipment!

Dave