[TowerTalk] Cable Conduit

[Dick Green]

> Does anyone have some pictures of a well designed,
> in-ground (buried) cable conduit system (eg, using PVC
> pipe)?

There are three pictures of conduit terminations on my website,
www.wc1m.com, under Cabling. The site is still under construction -- I have
a lot of pictures to upload.

Look at the pictures of the metal cabinet that has two PVC conduits coming
into it. These were installed by a professional electrician about 10 years
ago. Unfortunately, I didn't take photos of the conduits before the trench
was filled in. You can see how the conduits are terminated, and you can see
some of the lightning suppression system. There are identical terminations
at the tower and house end of the conduit runs, which are about 265' long.

The third pipe, 1" diameter, carries 220VAC power to a subpanel at a
motorized crankup tower. It was installed that way by an electrician --
directly into the house through an L-adapter. He was correct to keep the AC
out of the box with the coax and control cables, but the AC has no entry
panel, no suppressors, no connection to the single-point ground. I did put
suppressors in the metal junction box on the other side of the hole where
the cables enter the house, and connected the box to the single-point
ground, but I probably should install a weatherproof metal utility box on
the outside of the house for the suppressors and ground connection. FWIW,
the subpanel at the tower end has circuit breakers with built-in lightning
suppressors and the subpanel is connected to the extensive tower grounding
system (similar to the one I did for the new tower, which you can see under
Grounding.) 

Ignore the cabinet with one PVC pipe -- that's just a stub for direct-buried
cable to the big tower system, and I did that one myself.

What exactly are you looking for? I can tell you that each end of each run
terminates in a 90-degree sweep from the underground horizontal pipe up to
ground level. The end of the sweep is cemented into an expansion joint. A
short length of PVC pipe is cemented into the other end of the expansion
joint. The other end of the short pipe is cemented into a threaded adapter.
The threaded end of the adapter passes through a hole cut in the box with a
large hole saw. A thin threaded metal ring secures the adapter to the box. A
threaded plastic flange is screwed on top of the adapter, protecting the
cables from the sharp edges of the adapter. That's it. From there, the
cables connect to lightning suppressors. Cables from the suppressors enter
the house through the back of the box, using the same type of threaded
adapter used for the conduit termination.

You can see a 2 1/2" adapter destined for the second box laying in the open
box in the first picture.

The terminations are pretty typical for professional electrical conduit
installations in my area, and I tried to duplicate them for the second tower
system. The expansion joints are necessary when you have long runs of
conduit. There's a formula that tells you how much expansion you can expect
with a given length of conduit, and how to set the expansion joint depending
on that and the ambient temperature. You can Google for that information.
The expansion joint I put on the stub for the direct-buried cable is
probably not necessary, but we get a lot of frost heaves in our area, and I
wanted to relieve any upward pressure on the box. The joints didn't cost all
that much.

I got most of the parts, adapters, etc, at the local electrical supply
house. Home Depot has some of the stuff, but limited size selection.

Questions?

73, Dick WC1M