[TowerTalk] Lighting

[Tom Rauch]

> I may be wrong but my take on this is that many of us were
> told that structures not properly grounded would build up
static
> and be more likely to attract a strike.  I have also
wondered
> about the fact that tall grounded structures could attract
a hit.

But the charges come from the massive charge pool of the
earth and flow into the tower.

They are attracted there by the charge difference between
the clouds and earth. Grounding the tower wouldn't get rid
of charges, it would simply allow them to accumulate with
less resistance in the path.

One way to reduce the electric field intensity is to balance
the cloud charges, and that requires a path between the
cloud and earth. That's what we hope to avoid, because the
sudden equalization process makes a little noise and a tiny
spark we call lightning.

The other way would be to reduce the height of an object, or
make it blunter. Either would lower voltage gradient. If I
don't want a piece of metal in a capacitor to arc easily, I
either insulate it or make it very smooth. Bleeding off
charges requires a path between opposite charges, and we all
know that is what starts a lightning strike.

I think Jim Lux hit it on the head. It might have come from
Franklin's guess that his lightning rods bled off charges.

This is interesting, because I never realized until the
other day people thought reducing ground resistance reduced
hits.

73 Tom