[TowerTalk] Tower Grounding Method

[Mark Lowell, N1LO]

Greetings from Gloucester, Virginia

After perusing the load of messages in the archives about tower grounding
methods and materials, I used the following scheme to build a low-impedance
grounding system for my planned tower. In true Ham fashion, I improvised
with very commonly available materials wherever possible. Let me share this
method as one example of 'how-to' that I chose.

1) Use 1 ground radial per tower leg, 2 ground rods per radial, 6 rods
total.

2) On each radial, the 1st ground rod is spaced 8 feet from base, 2nd rod 24
feet from base (16 foot rod spacing). For better or worse, I did not
encircle the base with a ring.

3) Use 3/4" x 10' type L (heavy wall) common copper water pipe (about 80
cents/foot) for both radials and ground rods. This pipe provides lots of
smooth copper surface area for low impedance, yet enough total copper cross
section for current-carrying capacity.

4) Provide a flexible connection between the radials (rigid) and tower legs
using 2, 5/8" diameter by 3' long sections of flexible copper refrigeration
tubing in parallel. These come up out of the ground from the radial end, and
arc up, parallel to the tower leg, and are easy to bend, yet provide lots of
smooth copper surface area. Since the wall thickness is lower than the 3/4"
pipe, two in parallel are required for current capacity.

5) Make connections in the 3/4" pipe (radials & rods) by flattening the
ends, polishing with Scotchbrite abrasive pad (no metal wool!), and joining
with #6 size copper split bolts. A 1/2" through hole is just right for these
bolts. Since these bolts don't have much of a shoulder on them, they must be
modified. Modify the split bolts by flattening (in a vise) the 2 little
staked 'wings' that capture the anvil (the little jaw that slides in the
slot) in the nut so that you can take the nut off and leave the anvil. Put
the bolt and anvil through your drilled hole from one side so that the
'T'-shaped anvil head helps provide a shoulder to keep the small bold head
from pulling through, and apply the nut, of course, to the other side. This
little exercise earns you a copper bolt to avoid dissimilar metals.

6) Use copper-filled antioxidant liberally on all the copper-to-copper
joints. An excellent source is Versachem anti-seize paste #13, available
from Advanced Auto parts. It comes in a container with a brush attached to
the lid and is a heavy grease LOADED with copper particles. Hey, you can
also use this stuff on fasteners in your engine! After bolting the
connections, seal the antioxidant in the joint with electrical tape such as
Scotch Super 88.

7) Drill weep holes vertically through radial pipes every 4 feet or so
before burying. You don't want steam-flashover during a strike to explode
your work (wouldn't it be neat to watch, though?)! I used shallow
V-trenches, 4 inches deep, for the radials.

8) Sink the ground rod pipes by making them into water drills. Flatten one
end to form a nozzle with about a 1/8" elongated opening. Solder a garden
hose adaptor assembly on the other end. I used 2 90 degree street els, a
pipe thread adaptor, a 1/4" lever valve, and a garden hose adaptor in my
assembly. Using the 30-40 psi water from my well pump, and twisting the pipe
like a drill bit, back-and-forth, while pushing down, I was able to sink
each 10 foot pipe in less that 5 minutes. Don't sway the pipe side-to-side,
or you will make the hole too wide. Use the minimum valve opening to make it
work, so you don't wash out too much dirt and compromise the contact between
the pipe and ground. Take it all the way below grade in your trench, then
raise it up 6" or so (tap it back down in the trench later after connecting
to radial). Then, cut off the water, cut off the pipe with a tubing cutter
just below the adaptor assembly, and carefully desolder the stub so you can
reuse the assembly on the next rod. Flatten the end with 2 hammers for
electrical connections per above.

9) Connect the flexible jumpers to the tower legs by first gently hammering
the ends flat against the leg to form a large, curved contact patch over 2"
long. Apply a piece of stainless steel shim stock over the tower leg, and
clamp the tubing ends over the shim with all stainless hose clamps. Use
Noalox on all surfaces as an antioxidant. Don't use the copper-filled stuff
between the stainless and the galvanized tower leg (bad metal combination).
I found a perfect source of stainless steel sheet metal by using the tubular
shaped element that comes in the flexible compression pipe couplings used to
join sections of abs pipe. These little jewels, also in the plumbing aisle,
have a tubular rubber boot, a stainless cuff, (essentialy a rectangle of
thin sheet formed into a tube), and 2 hose clamps. Sorry, I don't know what
they are called.

10) Extend one radial up to your house and tie it in with the service
ground. Bring the pipe above ground to an entrance panel for your cables.
Solder the pipe together above ground using tees. Since this section is
primarily for dissipating surges and not direct strike current, soldered
joints should hold up fine, and are easier to make. Leave the branch of the
tee open so the pipe cannot collect water. Stuff the branch opening with a
copper potscrubber to keep bugs out.

Ok, it was long, but I hope you enjoyed reading about how I went about the
grounding. Thanks to all who have contributed to the reflector and spawned
my ideas. I hope this post helps someone else build a good ground system. I
feel that this will give me much protection from lightning when a hit
occurs, and I will sleep better at night when those 2am boomers roll
through. Well worth the $200 or so I spent in copper. I hope it works!

Now, I am shopping for tower sections......

Mark, N1LO, Gloucester, VA





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