At 08:20 AM 4/1/98 -0800, Dick Flanagan wrote:
>At 2:43 AM -0800 4/1/98, Malcolm Clark wrote:
>
>>Pete Smith wrote:
>>
>>[snip]
>>
>>> Well, the Polyphaser book and various other references talk about using
the
>>> rebar cage in your tower base as a Ufer ground, connected to the tower.
>>> Apparently this significantly increases the current-carrying capability of
>>> your ground system in the event of a lightning strike, but requires that
>>> the entire rebar cage be welded, not wired together, and that a good
>>> large-gauge electrical connection be made to the tower itself.
>>
>>[snip]
>>
>>That's really interesting. I respect Polyphaser's opinion but Rohn
>>specifically states that the rebar cage must not be welded. I'd love to
>>hear those two industry leaders debate their conflicting views.
>
>
>Discussing tieing vs. welding tower base rebar, the Polyphaser book (p. 14)
>states:
>
> "...it has been found that these wire ties are surprisingly effective
> electrical connections. ...One might think that the ties would fail
> under fault conditions. However, it should be remembered that there
> are a large number of these junctions effectively in parallel, cinched
> tightly..." (IEEE Seminar Notes 1970).
Dick's right -- I was quoting from memory, and remembered the part
immediately above his quote, where it says "It stands to reason that the
outer most sections of the rebar structure should be bonded together, not
just tied. If tied, a poor connection could cause an arc .... This has not
been the case... [continuing where Dick started]"
So apparently, weldinmg the rebar isn't necessary. I'd still like to know
why Rohn recommends against... the only thing I can imagine is that the
welds react with the copncrete for some reason. Perhaps this is a general
caution about rebar, though I've seen rebar cages being arc welded for
bridge structures, etc.
73, Pete Smith N4ZR
n4zr@contesting.com
"That's WEST Virginia. Thanks and 73"
--
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
|