[geeks] Whee! Lightning strikes, AGAIN!

[Phil Stracchino]

wa2egp at att.net wrote:
> -------------- Original message ---------------------- From:
> gsm at mendelson.com

>> A Franklin designed lightening rod (grounded point source) focuses
>> the ground charges and creates up leaders, forcing connections to
>> them.
>
> No, he did not.  The sharp point of the lightning rod causes the
> immediate field around the tip to ionize the air and dissipate the
> charge so the field doesn't build up enough to create the leader.
> the air needs to ionize the full length of the potential path.  This
> can be demonstrated with any van der Graff machine or other high
> voltage generating device.  See St. Elmo's fire.  Perfect example.
> Look at any power station.  Any turns in their conductors have
> rounded corners, no sharp points, so no charge will be dissipated.

Uh ... you just contradicted yourself.  You're saying, power station
conductors have smooth rounded bends so that no arcs will be produced,
but lightning rods have sharp points so that no arcs will be produced
(i.e, no lightning attracted).

In this, you're completely missing the point of lightning rods.

Van der Graaf generators have polished, rounded electrodes to keep the
local field as flat as possible adjacent to them, thus minimizing charge
leakage and ionization to prevent premature discharge and allow raising
the potential as high as possible.  Lightning rods, on the other hand,
have sharp points, and are set up as the highest point around, *because
THEY ARE INTENDED* to create leakage currents and attract lightning.

The purpose of a lightning rod is not to prevent lightning strikes.  It
is to prevent lightning strikes *from damaging buildings*, by attracting
lightning strikes in the vicinity and inducing them to strike *the rod
instead of the building*, and thus be harmlessly (in theory) conducted
to ground.



-- 
  Phil Stracchino, CDK#2     DoD#299792458     ICBM: 43.5607, -71.355
  alaric at caerllewys.net   alaric at metrocast.net   phil at co.ordinate.org
         Renaissance Man, Unix ronin, Perl hacker, Free Stater
                 It's not the years, it's the mileage.