Roger Halstead wrote:


The cluttering refers to a bottlebrush arrangement of multiple sharp points, but
the same idea applies to a single sharp point.

According to our electrical inspector it's not a myth, but I don't
know one way or another. However I do know that it would take little
to bleed a charge and a lot to control a strike. I also know that
every tall structure at the chemical company where I used to work had
lightening rods

Bleeding supposedly does just that. I prevents the charge from
building up to a potential that will help bridge the gap to the
feeders.

I don't know if I would call it a total myth, but I call it fairly risky
none the less. I know I sure wouldn't trust one to protect me from a
strike. I don't think they can bleed the charges from constant hard wind
and rain fast enough to do any good. It's like taking a whiz in a
whirlwind.

The last class I had at work on electrical safety was pro
lightening rods AND ground systems. (as was the one for skywarn from
the NWS)

I agree there, if he is talking about the traditional pointy lightning
rod used to protect other gear or buildings. I'm of the opinion strikes
can never be totally avoided, and the brush things are a waste of time.
I've heard of many reports of them being struck. Sometimes spraying hot
metal around and causing a fire hazard. And you still should have a good
ground even with those. To me, the only sure thing is expecting the
strike to happen, and safely controlling it's path to ground when it
finally does. So I'm firmly with polyphaser on that one. MK
--
http://web.wt.net/~nm5k

There is a short video available (saw in a search of lightning arrestor
systems) that shows the Empire State Bldg being struck several times, and
not once does the lightning "visibly" hit, follow, or otherwise act
impressed with the elaborate grounding system on the building. Taken as a
whole though, it must be effective, because the strikes do no apparent
damage, and they obviously get to the ground somehow.

JP

"Mark Keith" wrote
The last class I had at work on electrical safety was pro
lightening rods AND ground systems. (as was the one for skywarn from
the NWS)

I agree there, if he is talking about the traditional pointy lightning
rod used to protect other gear or buildings. I'm of the opinion strikes
can never be totally avoided, and the brush things are a waste of time.
I've heard of many reports of them being struck. Sometimes spraying hot
metal around and causing a fire hazard. And you still should have a good
ground even with those. To me, the only sure thing is expecting the
strike to happen, and safely controlling it's path to ground when it
finally does. So I'm firmly with polyphaser on that one. MK

Jack Painter wrote:
"Taken as a whole, though, it must be effective, because the strikes do
no apparent damage, and they obviously get to ground somehow."

True. I`m skeptical of claims of lightning avoidance by discharging the
earth beneath the thunder cloud. I think the protection is from
substituting a more attractive target to the lightning than the one you
want to protect.

I`ve worked with too many radio towers. Many had inverted Copperweld
ground rods bolted to the tower tops with the pointed end aimed up.
Function of the rods was protection of beacons and other appurtenances
atop the tower.

The towers still get lightning strikes but the beacons don`t get damaged
from the tower hits when there`s a Copperweld lightning rod up there.
I`ve seen broken and burnt beacons from towers that didn`t have the
rods.

A radio tower with a sharp-pointed lightning rod is very salient and
should discharge the earth under and around the tower, if this is a
prctical course. From what I`ve seen these lightning rods do not prevent
lightning strikes but they do prevent some of the damage that lightning
causes.

Best regards, Richard Harrison, KB5WZI