On 5/25/13 8:36 AM, Wayne Willenberg wrote:
While I am waiting for my 89’ crank-up tower to be built and delivered, I
thought I would get busy running the various control lines for the rotator,
the AC power for the motor that lifts the tower and, of course, the RF
cable for my antenna that will be on top of the tower.
I would like to place these lines underground from the panel entrance to my
shack to the base of the tower. (That total distance is about 175 feet)
My first thought was to run the cables through PVC pipe, and to use Andrew
LDF5-50A Heliax (7/8”) for the RF cable. Of course, I will have to use a
flexible coax from the base of the tower to the top of the tower.
I would really appreciate some advice before I start trenching. For
example,
1) It would seem logical not to put the RF cable in the same PVC pipe as
the 220 VAC wire for the motor and the power and control lines for the
rotator.
And combining power lines and "Class 2 power limited" low-voltage
circuits in the same conduit/enclosure/etch is specifically prohibited
by most electrical codes.
If it is better to separate the RF cable from the other lines,
how far apart should the 2 PVC pipes be?
They can be next to each other. the concern isn't electrical, it's
mechanical: in order for there to be an inadvertent short from power
circuit to "low power" circuit, you'd have to have two barriers fail
(i.e. conduit walls).
You can combine the coax and the low voltage control lines in one
conduit: they're all "power limited" circuits.
2) Should I drill holes in the bottom of the PVC to allow any water that
gets into it to drain away?
That's a subject of much discussion and subject to local conditions,
like whether the animatronic owl needs to be periodically reoriented as
the Earth's spin axis changes.
I don't drill holes in mine, but I live in relatively dry Southern
California, and I make sure the stub up ends at least a foot above
ground surface (so that sprinklers, and such don't wind up putting water
into the it). Mostly when I pull the wires out, they're dry, but every
once in a while they're damp. The only time I had "wet" (as in the
conduit was full of water) was when there was a shovel and big rock
induced break in the conduit that I didn't catch early on.
Thanks as always for your help with my first tower.
Wayne, KK6BT
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