[TowerTalk] Conductive Cement Reply and further comment DE K0FF

[K0FF]

This cement thread is interesting, but may be of limited availability. Just
a reminder about a similar topic that has been touched upon here on TT
before. It's easy and cheap to enhance the conductivity of the disturber
soil around the tower site and ground rods at the time of construction. The
recommended material is call coke fly . Simply a carbon powder that is a by
product of industrial processes, and is usually sold for a few cents a
pound. When you buy an artificial groundrod from one of the lightning
protection supply places ( Like Thompson's) all it consists of is an 18 long
inch copper tube of about 4" diameter, capped on each end, and filled with
this powder. A thousand tiny holes drilled all over the surface of the tube
allow the interaction with the surrounding soil. On the top cap is fixed a
short piece of 1/2" copper pipe, and that's all you see when it's buried.
{Note: KØFF sits on the edge of a river bluff and the soil depth is zero to
at the very edge, and increases slowly to about 10 feet only on the top, so
special care has to be taken at each of the 7 tower locations depending on
available depth. This concern expends to concrete pads as well as
grounding.}
Now the coke fly is not available in my small town, but the idea seems of
jazzing up the soil with carbon seems sound, so with little investment, and
nothing to use, I just use charcoal. Leave it in the bag and run over it
with your car wheels a few times. Plenty of powder and small chunks
results.

It's been suggested that groundrods that are driven in undisturbed earth
have better contact with the soil that those that are just buried or
installed via the water method. This may be true at the beginning, but over
time my experience with any object that's in the ground shows that the soil
quickly compacts itself around and incorporates the object fully.

By whatever method the rods are installed, they should indeed be totally
under the surface, including the connection ( see archives), but again I
take a little different approach than just throwing dirt on that carefully
made and protected joint ( with electrical goo ...archives). For about 6" at
the surface around the flush groundrod, I dig a little pit, and go ahead
and put the strap*, wire whatever onto the rod with an all bronze clamp,
using some electrical goo. Then partial fill the pit with charcoal dust,
and then top it with an upside-down aluminum soda can with the top cut off.
This can sits flush with the surface, and can easily be excavated for
inspection and / or repair of the (still clean) connection joint. Cover the
joint area only with the can, as the charcoal dust needs to be exposed to
rainwater to work.


* Although flat copper strap shows the lowest inductance for lightning, I
have unfortunately seen even the 2" variety have stress cracks all the way
across, and in one instance it parted. All towers sing / resonate in the
wind, and I suspect metal fatigue to be the culprit, especially if the
strap contacts the edge of the concrete pad midpoint. As a result, since
each towerleg has it's own rod anyway ( with buried  perimeter ring of 2"
strap), I use a combination of strap, heavy round wire, and copper braid,
all on same tower.

References:
www.harger.com
http://www.bdcast.com/home.html

http://www.inducomm.net/
www.polyphaser.com

http://www.hut.fi/Misc/Electronics/docs/surge/telesurge.html

http://www.tlpinc.com/


Happy Building, Geo>KØFF
http://homepages.dstream.net/K0FF

-----
Subject: [TowerTalk] Conductive Cement


> TT:
>
>      As promised, here's the pricing info on the cement (called Earthlink
> 101):  80 cents per pound.  The manufacturer (Grounding Systems LLC,
> 440-543-8580) recommends 8-10 pounds of cement per linear foot of trench
(16
> to 20 inches wide) > 73 de
> Gene Smar  AD3F




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