[TowerTalk] corrosion at clamps

[Bill Aycock]

I am putting up a new (to me) tower, and am in the mixed 'plan-ahead' -
'doit' mode.  What this means is that I have decided on the basing, dug a
hole, and cast some concrete.  I decided not to ground within the base, for
various reasons, but will have extensive grounding around the tower.

I am now contemplating the corrosion situation with regard to the
interaction of Copper- Bronze- Iron (things DO get scratched) and
hot-dipped galvanized. I have read lots here, but, the confusion comes when
I see what (supposed-to-be) professionals do. 

The local power people will clamp copper grounding wire directly to
galvanized iron rod. This is supposed to promote local corrosion, according
to what I read here. To make this worse- the actual clamp is Bronze, with a
copper bolt to tighten the clamp to the wire and rod. The contact surfaces
here are : copper to Bronze-copper to galvanized- Bronze to galvanized-.
An additional arrangement I have seen is a copper coil on the base of a
pole, running up to the top, where it is hooked into the galvanized
fittings that hold the transformer up.

The telephone people will apparently attach to anything that looks like it
might go to earth somewhere. In one case- I found the "ground" was a piece
of four-conductor house phone wire (#20 or 22 ?) with all four wires
together, leading under the house, to the house panel ground. Maybe that
was why a strike over a mile away came in the phone line and blew my computer?

What I have read, and intend to use, is stainless shim to protect copper
from Galvanized, where I clamp grounding conductor to Rohn 25. I know that
exothermic welding is 'best', but want to be able to change, later, as I
add radials, without having to cut .

The soil here is sandy loam, typical of land alternating between crops and
woods, as succeeding generations change their habits. Actually, there is a
layer of Sandstone not too far down, and 8' ground rods frequently hit it.

Any thoughts or comments will be read with appreciation.

Bill



Bill Aycock   W4BSG
Jackson County, AL
EM64vr
W4BSG is "vanity" this time, but was 
earned by exam in 1954, the first time.

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