In a message dated 98-06-03 11:44:27 EDT, dick.green@valley.net writes:
> There seem to be three schools of thought -- 1) disconnect everything, 2)
> try to prevent a strike by mucking with the corona, 3) try to dissipate a
> strike. Some advocate combinations of these approaches (i.e., one solution
> would be to disconnect all cables, use porcupines at the top of masts, and
> use lightning arrestors connected to a superior ground system.) But due to
> the random nature of lighting strikes (i.e., the impossibility of
conducting
> reproducible tests), I doubt that this debate will ever be resolved.
I'm sure you mean resolved in the amateur community. Commercial
communication site ground systems and standards are well documented and
accepted by those users. In their case, an outage due to a lightning strike
would result in the ultimate problem - loss of revenue - and that's not
acceptable.
I have never seen in any credible literature relating to grounding
systems where disconnecting anything is recommended. I think it's reaching
'old wife's tale' status. And don't forget that most of the people
recommending it (hams) only have their anecdotal experiences to back it up.
Polyphaser HAS a lightning generator in their factory and they have
conducted thousands of tests of lightning in general and their products
specifically.
>
> I, for one, haven't heard many stories about commercial B/C stations with
> proper lightning protection being knocked off the air, especially in my
> local area. The ones I have heard concern towers at the tops of mountains
> where it is difficult to install a proper ground system.
Installing an effective ground system is possible for virtually any type
of outdoor installation. While my company was installing a tower system on an
Eastern Washington mountaintop, a lightning storm came through the day after
we got the ground system and lightning arrestors, etc. hooked up. We watched
the tower take a direct hit (very dramatic!) and there was zero damage to any
equipment and no downtime as a result. This was in very rocky soil. All it
takes is the desire to do it right and the resources to do it.
>
> I opted for the full Polyphaser solution -- surge protectors at both ends
of
> every condutor coming into the shack, including coax, rotor, control,
> telephone, 110VAC, 220VAC, etc., with a single point ground connected by a
> heavy buried conductor to an extensive ground system at the base of the
> tower (12 rods bonded with heavy Cadwelded radial wires, plus the
240-radial
> field for the 4-square.)
Beautiful - you won't have any problems.
>
> Also, it makes no sense to disconnect those wires in the shack --
> you don't want lightning coming in the house and jumping from those
> disconnected cables to anything that's grounded. A freind of mine with a
> 100' tower uses the disconnect method and last year he heard arcing in a
> closet where a bundle of cables comes into the house. Evidently, the surge
> was jumping from a cable shield to some grounded piece of metal (maybe a
> water pipe.) I think you have to disconnect the wires outside and pull them
> well away from the house. And then there are the Telco, cable TV, and AC
> power conductors that enter your house... do you disconnect them too?
> Outside the house?
>
> The disconnect method only works if 1) you do it religiously, 2) you can do
> it well in advance of lightning getting close enough to induce surges (have
> you ever been surprised by an unforseen lightning bolt?), 3) you do it
> outside the house, and 4) you can be absolutely sure that you got all the
> cables disconnected (there have been many stories about hams forgeting that
> one cable -- like the phone line to the modem -- with disasterous results.)
>
There are two ways you can get transient damage - one is from a direct
hit but the more insidious one results from a direct or induced hit and comes
in from miles away via your telephone line, cable tv, power line, etc.
> Most hams say that nothing will protect you from a direct hit.
Do you think that's true? Another 'old wife's tale.
73 and tnx for your interesting and informative post, Steve K7LXC
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