David,
It depends on how much cable you plan to put through the conduit, how you
plan to put it through and how much room you want to leave for future
expansion. You can either build the conduit around the cable or you can pull
the cable through after the conduit is laid. I've tried it the former way
and it's not as easy as it sounds -- things get messy in the trench and
there's PVC cement that can get on the cables, etc.
The pros pull cables through the conduit. The rule of thumb for pulling is
that the diameter of the conduit should be at least twice the diameter of
the cable. The usual procedure is to attach a string to a soft foam ball or
cylinder and suck the ball through the conduit with a vacuum cleaner. The
string is then used to pull a nylon rope through the conduit, which is in
turn used to pull the cables through (plus another length of pulling rope
for adding cable in the future.) If the cables are stiff and/or near the max
capacity of the conduit, you may need to coat the cables with some pulling
lube (available at electrical supply houses.) You can use hardware-store
white plumbing PVC, but the pros use grey stuff specifically made for
burying cable. That's also available from electrical supply houses. You
should not use those 90-degree angle pieces from the plumbing section of the
hardware store if you plan on pulling the cable through. The bends are too
sharp, especially if the cables are stiff and/or you are near the max
capacity of the conduit. You should use a "90-degree sweep" joint that
gradually makes the transition from horizontal to vertical. Those are
available from electrical supply houses, too.
You can certainly just use plumbing PVC and cram a lot of cables into the
conduit, but you may be sorry later if you need to add more cables or
replace the existing cables.
73, Dick WC1M
> -----Original Message-----
> From: towertalk-admin@contesting.com
> [mailto:towertalk-admin@contesting.com]On Behalf Of David
> Sent: Tuesday, July 02, 2002 8:34 PM
> To: TOWERTALK@contesting.com
> Subject: [Towertalk] Coax conduit
>
>
> Getting ready to dig the concrete base for my new tower and plan
> to run a 1
> 1/2 inch PVC pipe from my shack about 30' away and up through the concrete
> base. This pipe is big enough to carry several coax lines plus the rotor
> cable, so is there any reason I would want to run a separate pipe for
> anything else? The reason I ask is because I see photos of a ham
> installing a tower on the texas towers website and he has two PVC conduits
> coming up through his concrete base.
>
> David, K4ZZR
>
>
>
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