The tower is Cadweld bonded to every single stick of rebar at the bottom
of the cage, representing 16 cross pieces each 9 feet long (eight sticks
in each direction) plus the bottom perimeter rebar comprised of two
pieces 20 feet long that were bent and overlapped to form a square shape
9 feet on a side. That was a lot of Cadwelds, but I bought the graphite
mold (actually two of them) as unused surplus on eBay, and I got the
weld metal powder also from eBay (different vendor) for less than $1 per
shot. The other end of the copper wire was Cadweld bonded to the tower
base using a different mold I found on eBay for attaching wire to flat,
vertical steel. I can give you the model numbers of the molds if you're
interested ... Erico has a pdf document on their website describing most
of their molds.
I didn't Cadweld bond the sides of the rebar cage because I didn't feel
they would be a direct path to ground anyway. The base of the HD-70
tower extends per the manufacturer's specification all the way down to
within 6 inches of the bottom of the concrete, so lightning energy would
actually have to travel back "upward" to exit the sides of the foundation.
By the way, I discovered that making your own mold is not really very
difficult. Check out http://tinyurl.com/5scf35 * *
I mentioned in the page on making my own Cadweld that I was thinking of
making my own weld powder. I eventually did so and I would strongly
recommend NOT doing it. The materials are trivially easy to get, but
the particle size is pretty important. The stuff I got on eBay
(aluminum powder, copper oxide) was pretty finely ground, and it reacted
so quickly that it just flashed. At least I was cautious enough to test
a very small portion of it behind a shield before trying it in a mold
... I think it would have been a bomb with larger quantities confined in
a small space. I need to edit that portion of the web page ;)
73,
Dave AB7E
Scott McClements wrote:
> On 5/29/08, David Gilbert <xdavid@cis-broadband.com> wrote:
>
>> That's why Cadweld connections should be used to bond to the rebar, and
>> it isn't any more difficult to do that than to bond the ground wires to
>> ground stakes. I bought the mold and materials to do so on eBay for
>> less than $30.
>>
>
> I noticed on your installation, best I can tell, you used wire ties on
> the rebar. Is the tower bonded to all the rebar pieces?
>
> -Scott, WU2X
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