In a message dated 97-04-16 21:44:20 EDT, wwilson@ccpl.carr.lib.md.us (Wayne
Wilson) writes:
> Does the distance of the tower ground rods have any effect?
>
> What is the preferred distance, 6 inches, 2 foot, 10 foot?
>
The practical hemisphere of influence for ground rods is twice their
length. In other words, a ten foot ground rod has a hemisphere of
approximately 20 feet. So does the adjoining ground rod. The rods should be
spaced 20 feet apart so that their respective hemispheres just touch. If the
rods are closer together, you aren't getting the maximum effectiveness from
them. Farther apart is better than closer together.
If your question was "how far to space the ground rods from the tower"
then the answer is to get them as close as practical to the tower legs. The
connecting wire should have big lazy bends in it and not sharp ones. The
sharp bends are high impedance points which is what you're tryin to avoid.
Putting a copper ground wire in direct contact with the galvanized tower leg
is asking for trouble. Use a little piece of stainless steel sheet between
them and liberally apply antioxidant for best results. You can clamp the
thing together with an SS hoseclamp.
Then have several ground rods in series attached to each leg using the
above distance to really enhance the job.
BTW, commercial ground systems use a value of 5 ohms for ground system
resistance for their target value. You've got to have a GOOD ground system
to achieve it.
Once the tower legs are grounded adequately, you're ready to move on to
the remaining steps of your ground system installation.
73, 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
|