[TowerTalk] tower ground question]

[David Gilbert]

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 at 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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