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[TowerTalk] Schedule 40 in New England

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Subject: [TowerTalk] Schedule 40 in New England
From: ("Dick Green".)
Date: Sun, 14 Sep 1997 18:59:11 -0400
It must be the season for planting conduit because mine just went in last
week. Although my installation and solutions are rather different from those
described by K1VR, I do agree with much of what he says if you're doing the
job yourself. However, I thought you all might be interested in hearing
about my happy but financially painful results.

Most of the complication arose from the fact that my tower site is located
250 feet from the house and requires a 110VAC 20A circuit to operate the
tower winch motor (U.S. Towers 72' tubular crankup.) For aesthetic reasons,
suspended cables were out, so, by code, the line had to be run in conduit
buried at least 4 feet deep to avoid frost heaving (common in NH.)  As long
as I had to dig a long, deep trench, I elected to install three runs of PVC
conduit: a 1" diameter pipe for the 220VAC line (splits into 110VAC at the
tower), a 2 1/2" diameter pipe for four multiwire control cables (tower
motor, rotator, antenna switch, phasing switch for a nearby 4-square), and a
4" pipe for RF cables (initially two runs of LM400U, probably to be followed
by 7/8" hardline at some point.) This may seem like overkill, but there's
logic to it. By code, the AC has to be in its own conduit. I wanted to leave
room for at least 2" of RF cables and over one inch of control cables. The
rule of thumb for easy cable pulling is to make sure that the conduit it at
least 50% larger than the diameter of the cables you are going to pull
through it (especially when you have a long run like mine!) That pretty much
dictated three conduits.

For various reasons, not the least of which was the size of the trench and
the fact that AC power would run through it, I elected to use a professional
contractor to dig the trench and lay the conduit. To those contemplating
something similar, I should say that if you use the right contractor, you
will get great results -- but it will be very expensive. Labor and machines
to dig the trench are very expensive, as is 750' of conduit (the 4" stuff is
*really* expensive.) But my contractor supplied the sunlight resistent
Schedule 40 pipe (the grey stuff), along with all the standard parts for a
professional termination job (gradual 90 degree sweeps with 16" radii for
coming up to grade, expansion couplings, threaded terminations, etc.)

One nice touch was that I had 250 feet of 2/0 stranded bare copper wire
buried with the PVC to connect the tower grounding system with the
single-point ground at the house. The contractor was able to supply me with
20 8' 5/8" ground rods at a great price. I plan to Cadweld all the ground

To avoid weather and critter problems, the conduits will be terminate in
junction boxes. At the tower, there will be a pressure-treated wooden
pedestal with a large box for terminating the RF and control cables. This
box will have a metal panel inside for mounting lightening arrestors for all
lines. RF and control cables will exit through the bottom of the box, so
this is the only hole that will have to be sealed from critter invasion. The
AC power will terminate in a smaller weatherproof box, probably with circuit
breakers. At the house, the RF and control cables will terminate in a
similar box (metal plate for more lightening arrestors, etc.) but the cables
will exit through the back of the box into the house.

Now for the painful part: No sooner had the backhoe started digging the
trench than it hit a large seam of ledge less than a foot under the surface.
Continuing down the hill to the tower site, two gigantic house-sized
boulders were hit as well. This required hiring a bulldozer equipped with a
powerful hydraulic hammer to smash the rock to bits. Even though each rock
obstruction was only about 3 feet by 4 feet, It took the better part of a
day and a half to chip them out of the way. That increased the cost of the
trench by about 50% (and it wasn't cheap to begin with.) Ouch. Welcome to
New England. Of course, I was aware of the risk of hitting ledge before we

Anyway, it's all over but the terminations. For those who remember my
earlier posts, the concrete base for the tower has been poured as well. We
did manage to get a cement truck down the steep hill right to the hole, so
this part went better than expected (the alternative was an expensive
pumping job, hauling it by backhoe, or using a portable mixer.) Although I
spec'ed a 3' x 3' x 6' hole, the excavator told me that it would be more
like 3' x 4' x 6' because of the size of his bucket and how he would have to
dig the hole. That was fine by me and the contractor bid a fixed price for
the job. For some reason, the excavator dug the hole too deep -- 8 feet!
Also, the upper part of the hole is more like 4' x 5'. In the end, it took 7
yards of concrete to fill the hole! Guess the contractor won't bid a job
like that on a fixed fee again (unfortunately, ledge removal was explicitly
ala carte in the bid.) So I guess my tower base won't be going anywhere...

73, Dick, WC1M

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