Hi. I'm planning a 100-foot Rohn 55 tower with a pier pin foundation. On
Thursday I noticed it had been about 40 days since my tower building permit
application got zoning approval and the appeal period expired (yay!) Curious
why I hadn't received the permit yet, I called town hall and the admin said
there was a note in my file from the electrical inspector asking that
certain requirements be met (why they hadn't notified me is a mystery, but
that's bureaucracy for you.) The admin quickly read the note to me over the
phone (she was in a hurry -- it was quitting time) and left a message for
the senior building inspector to call me (the electrical inspector is out on
medical leave.) He hasn't called yet, so I have the weekend to think about
my reply to the note.
The note said all rebar must be bonded to the ground grid, and inspection
will be required prior to backfill. My plan showed a ground system with 36'
radials made of 1/0 wire Cadwelded to ground rods every 12 feet, and I have
no problem installing a Ufer ground connecting the rebar cage in the pier to
the radial system. I was thinking about doing that anyway, but hadn't done
the research on it yet. I'm a bit surprised because our town is very small
and has traditionally not had stringent building codes. Last time I put in a
tower (1997), they didn't have any engineering requirements at all (they
still don't require loading calculations, wet stamps, etc.)
First questions: Are Ufer grounds commonly required by code these days? Have
any of you out there in TT Land been required to install a Ufer ground?
What's the best way to bond the pigtails to the rebar?
A bigger concern is that I was going to try to dig the 2.5' x 2.5' x 4' hole
by hand in order to get a nice square hole exactly to the required
dimensions and pour the concrete against undisturbed soil. An excavator will
be faster, but past experience leads me to believe the hole dimensions won't
be perfect and I would end up needing a wooden form. Besides, the Foundation
Notes in the Rohn catalog say that, except for pier-and-pad installations,
the concrete must be poured against undisturbed soil. That's what I've
always heard one should do. So, I'm planning on telling the building
inspector that the manufacturer's specifications call for doing the pour in
undisturbed soil and that they need to inspect the Ufer ground before the
pour (i.e., there won't be any form and there won't be any backfilling
unless I can't dig the hole by hand and have to use an excavator.)
Second questions: Is it really better to pour against undisturbed soil
rather than using a form? Would a form for a padless pier be a bad violation
of Rohn's specs?
Further, it's not clear from the note whether the electrical inspector wants
the anchor footing rebar to be bonded to the ground system, too. I don't
want to do that for several reasons. First, I'd have to make the radials at
least 80 feet long with a lot more ground rods. Second, the guy anchors
won't be electrically connected to the tower because I'm planning on using
phyllistran guys, so there should be little danger of a lightning strike
compromising the anchor concrete. Third, as recent posts suggest, anchor rod
corrosion can be accelerated if they are connected to the ground system.
That's another area I haven't researched yet (i.e., whether to spend $1,500
to protect my anchors from the battery effect.) I would think that
connecting the rebar to ground would have the same effect.
Third question: Has anyone out there been required to connect the rebar in
the anchor pads to the ground system?
Finally, the note (which I haven't seen yet) says something about conduit
for electrical, radio and control wire routing to the tower (the run will be
a little over 200'.) My plan shows "conduits" (I used the plural) for AC and
other cables to the tower. My guess is the guy just wants to make sure I'm
not running AC in the same conduit with the other cables and/or wants to
make sure I know the code requires electrical conduit to be buried at least
4' deep. But since filing the application I'm reconsidering whether I want
to run conduit to the tower. I know the code would require me to do that if
I run AC, and if I run one conduit I might as well run several. But AC isn't
required -- it's just a nice-to-have, handy for rotor testing, plugging in a
rig, power tools, etc. The decision will rest on just how expensive it will
be to run the conduit. I haven't gotten quotes yet, but I know it isn't
cheap to dig a 200' long 4' deep trench. But the real issue is whether
there's ledge in the way. There was ledge when we dug the trench for my
first tower (a motorized crankup that required AC), and it was *really*
expensive to pound through it. Bottom line, if there's ledge in the way or
the cost is otherwise too high, I don't want to run conduit to the tower. In
that case, I would forego the AC and just direct bury the hardline and
control cables in a shallow trench. My worry is that the electrical
inspector wants me to use conduit even if I don't run AC.
Fourth questions: Do building codes address non-AC cable runs? Has anyone
out there been required to install conduit just for coax/hardline and
low-voltage control cables?
Our town has issued very few amateur tower permits (maybe four since the
late 80s), so they don't have a lot of experience with it. I think our local
inspectors are probably pretty reasonable people and if I can show them that
common practice is otherwise, they'll accept it. But if it's in the code,
then I may have to do it.
Would appreciate any knowledgeable comments on the subject.
73, Dick WC1M
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