Jim, Nick, and All,
Thanks again for the advice. Good point, I will flatten and ss bolt all
ground pipe connections? no solder.
Obviously the tower is grounded to the slab by the bottom section being
encased in it so I will just be creating parallel paths to ground. How
about installing a Ufer ground down at the bottom of the foundation (in the
9x9 pad) AND installing the ?ring? of copper pipe all around the outside of
the pier when we backfill (with bentonite added? it?s cheap)?
It?s probably overkill, especially considering that my present tower is not
grounded other than by the base bolts, but it?s cheap and easy to do at this
point so why not? While I?m at it I think I?ll add another ground rod for
the shack. It has two now but one of them is approaching 20 years of age.
Unfortunately, no more tower progress until after the holiday. I had to
spend yesterday (and today) working on a house we are selling.
I hope you all have a great Independence Day holiday!
73 ? JC, K0HPS
From: Nick Pair [mailto:firstname.lastname@example.org]
Sent: Sunday, July 02, 2006 11:26 PM
To: email@example.com; firstname.lastname@example.org
Subject: RE: [TowerTalk] Grounding base slab and pier tower bases
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.
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