Hello JC,
I would still encase the cu pipe in the concrete for several reasons. First
the concrete enhances the contact area between the conductor and the soil.
Second it isolates the cu from the soil which contains sulpher. The sulpher
will bond to the cu making copper sulfate which will lower the surface
conductivity. Third no soil enhancement needed. Try to keep undisturbed soil
next to concrete pour anyway, for best load bearing ability, which your
foundation size was based on.
Nix on the solder for underground and ground conductors in general. The NEC
doesn't allow it. Another consideration is the fact that its introducing
dissimilar metals to a acidic environment. For your use a flattened, bolted,
stainless hardware connection would suffice anywhere you need to splice or
attach. Try to avoid splices if you can.
All cell site towers are grounded to the rebar and to everything that can
conduct in a 50 foot radius around them. The only cravat is they don't rely on
the rebar soley to carry the current to ground grid. I've never heard of one
falling after a strike or even multiple strikes. After all the base stub or
bolts are in the concrete too as a parallel path and they present no problems.
The radius is the only was to go. As large as you can and in no case less than
6".
Concrete is such a good conductor that a large ( hundred square foot or
better ) metal sheet (16 Gage min.) laid directly on clean concrete is used for
grounding at 911 com centers in existing building basements where access to
grid and rebar is limited or too great a distance away.
I've done quite a few cell sites for different cell companies with different
contractors and different inspecting jurisdictions. The engineering spec's were
pretty much similar and of course NEC always the same. Feel free to bounce any
questions or ideas off me on this subject.
If you lived in a more lightning prone area I'd recommend a lightning discharge
device for the tower top. They do a good job of keeping the tower potential
below where a leader arc can be created preventing a strike from occurring to
the tower and a radius equal to the height around it.
Nick WB7PEK
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