In a message dated 98-05-28 21:53:34 EDT, 10eesfams2mi@mass1-pop.pmm.mci.net
writes:
> > Shouldn't this be prevented from happening if a ground wire (or better
> > yet, low inductance flat ground strap) is run from the tower base along
> > side (and burried below) the antenna cables and is terminated at the
> > ground rod outside the shack wall, which is then connected to the
> > bulkhead?
>
> A nice low impedance path from the tower to the house won't ground
> anything, a nice wide surface area connection to earth will.
Let's see if we can start another holy war. It's been kinda quiet around
here the last couple of days.
" A nice low impedance path from the tower to the house" is a good
start. Yes, it's not a 'ground system' but it's something that needs to be
done. What a 'lightning protection system' should do is have everything bonded
together to minimize potential differences. It's these potential differences
that cause the arcing and assorted damage to equipment. It's the potential
difference of the tower and the earth it's sitting in. It's the potential
difference of the tower and cables. It's the potential difference of your
telephone line and earth. It's just about everything.
"A nice wide surface area connection to earth will." With 'normal'
soil, a solid copper wire (large - I can't remember the gauge) ground system
provides adequate connection to the earth. Commercial ground systems are built
to be 5 ohms or less. The times when 2-4 inch wide copper strap is helpful is
when you've got really poor soil, or rocky. It puts more surface area in the
system.
>
> > Doesn't the lightning surge current basically get shunted to
> > ground if this arrangement is used?
>
> Only with a very good ground.
True but isn't that what hams in lightning-prone areas would like to
have?
While I appreciate the theory (I'm always looking for good information),
I think what most TowerTalkians want is "how do I do it?". You know, the
PRACTICAL stuff. And that's why I rate Roger Block's Polyphaser grounding book
as barely useful. It's real long on the theoretical and the esoteric
engineering data but it's real short on practical construction tips.
Cheers, Steve K7LXC
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|