Craig:
Tower Rule of Thumb: You can never install too big a conduit. (This
is similar to: You can never have too many antennas.) I'd recommend not
designing your conduit system for what is known, but for what is unknown,
i.e., your future tinkering. For example, I'd recommend you install a
single larger Sched 40 PVC conduit (maybe 3 inches) for all your coax and
control cables. Carlon makes just such conduit systems and fittings. Bring
this conduit into a steel box above ground, through the appropriate threaded
PVC fitting. (Hoffman makes bunches of such enclosures to choose from.)
You can install this box on a couple vertical pieces of Unistrut (ask the
guy at the industrial supply counter where you get your PVC and enclosures)
held in place with a bit of concrete in front of the tower foundation, or in
the foundation concrete itself. You can install a coax switch ( I told you
you'd have future plans!) in this box. You can also install your Polyphaser
suppressors for the coax through the side of the box and ground the whole
thing for lightning protection. Your control cable suppressor would mount
to the wall inside the enclosure. You can bring the coax out of the
enclosure via the Polyphaser arrestors. The rotator control cable comes out
the bottom of the enclosure through a half-inch threaded bushing. (Ask the
industrial supply counter man for one of these, too.)
For the electrical service to the motor (and an auxiliary receptacle
for drills, etc., another future need) install an outdoor-rated fused
disconnect switch on another couple pieces of unistrut, or below the Hoffman
enclosure. (Watch out where you route the largish PVC for the coax, so you
don't interfere with mounting the disconnect.) Run the electrical service
to this switch via a one-inch PVC conduit. (National Electrical Code
requires separate conduits for power and non-power conductors.)
The ground conductors can be routed from the tower legs into the earth
through pieces of garden hose. The hose is resilient and will not be
damaged when (not IF) it's hit by the lawn mower. PVC conduit won't survive
as well. Plug up the above-ground ends of the hose with electrician's putty
(see the man behind the supply counter again.) And don't connect the ground
conductors to the legs right on top of the concrete. You'll create a
high-reactance right-angle joint that the lightning won't be inclined to
follow to earth. Attach the leads about a foot or so above the concrete,
and let them follow a gentle curve into the hose pieces and to the earth.
At the base of my tower, I have just such a Hoffman enclosure,
arrestors, coax switch, garden hose, etc. (I can send you a couple of
photos if that'll help.) I attached the Unistrut pieces directly to my
tower angle pieces with J-bolts, then attached the enclosure to the
Unistrut. I would advise against installing unsupported PVC conduit as
you're suggesting. When you eventually pull more coax through it. it could
snap, depending on the force you're exerting on the coax.
I referred to Bill's N3RR web pages for lots of good design info on
grounding systems. You can find his site at: http://users.erols.com/n3rr/
. Good luck and let us know which way you decide to go.
73 de
Gene Smar AD3F
----- Original Message -----
From: "Craig Sande" <craig.sande@sbcglobal.net>
To: <towertalk@contesting.com>
Sent: Sunday, October 31, 2004 8:53 PM
Subject: [TowerTalk] Conduit runs in tower base
I am getting ready to pour the base for a 70 foot crank up tower by Tashjian
Towers. Initally I plan only one run of Bury Flex by Davis RF to a remote
coax switch on the tower, a control line for the coax switch, a control line
for the rotor, and power & control lines for the tower motor with remote
control option. I would like a neat installation, as it will be in the back
patio area (e.g. concrete or pavers will surround the base after
installation).
Does the following sound ok (tower newbie here)? Three sweeps of 3/4 or 1"
conduit terminating just below and inside each tower leg on top and exiting
into trenches radiating from the tower for the buried ground radial system
(2-0 stranded copper); one 1" conduit sweep to buried conduit for the 120
VAC for the tower motor; and two 2" conduit sweeps to buried conduit run for
the RF cable(s) and low voltage lines.
Where should I terminate the conduit sweeps for the 120VAC, RF, and control
lines relative to the tower cage so that they won't be in the way of the
tower, but won't be too far away?
Should I put a double 90" at the top of the sweep for the coax to keep rain
out, or connect the two 2" sweeps to some sort of metal junction box? How
should I stabilize the junction box if used (e.g. metal channel coming out
of the concrete or simply attached to the conduit)?
Any suggestions greatly appreciated!
Craig, AE7I
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
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