A lot of good thoughts in this thread. As a summary and adding a couple of
thoughts:
1. Always terminate conduits in weatherproof boxes at both ends to reduce
rain infiltration.
2. Always leave a messenger cable in the conduit - it will always be
difficult to pull new cables in later, but you don't stand a chance of
pulling a new cable in without one. And for ease of replacing cables, fill
conduits no more than 30% of cross-sectional area.
3. You can never seal a conduit well enough to eliminate condensation over
the years. Bury the conduit below the frostline for your location to
prevent freezing.
4. Never use PVC bends or elbows (45-degree or 90-degree) below grade.
Tension on the pulling rope puts a lot of strain on the elbows, often
causing cracks in or collapsing of the elbow, allowing infiltration of dirt
or water. Use galvanized rigid steel conduit (GRSC) threaded elbows
instead.
73, Sam AE5L
----- Original Message -----
From: "Jim Rhodes" <jimk0xu@gmail.com>
To: <towertalk@contesting.com>
Sent: Monday, February 07, 2011 6:24 PM
Subject: Re: [TowerTalk] Underground conduit question
> For my feedlines I use a plastic electrical box on the side of the house
> with a 4 inch conduit coming out of the wall with 4 inch conduit coming
> out
> of the bottom of the box going underground to the tower base, where it
> comes
> up again into another box (these are both 12x12x6 boxes) There is a drain
> hole covered by plastic screen in the middle of the run in a deliberate
> low
> spot. For feedline access I use "strain reliefs" bought at one of the
> local
> big big box stores. That way there is no way for even the smallest critter
> to get into the conduit. I stuff some wadded up plastic into the inside
> end
> of the pipe to keep the cold air out though. BTW, the tower is about 5
> feet
> from the basement wall.
>
> On Mon, Feb 7, 2011 at 1:54 PM, Rroger (K8RI on TowerTalk) <
> k8ri-on-towertalk@tm.net> wrote:
>
>> On 2/7/2011 1:55 PM, Peter Dougherty wrote:
>> > Hi all,
>> > Several years ago I had a run of 4" solid white PVC tubing run on a
>> downward
>> Very important...How long is this run and how deep.
>> > slope from my basement, under the finished portion of my back lawn then
>> > opening out into an un-maintained part of the yard in which my receive
>> loop
>> > and 160 TX antennae are located. All was thought to be well until I
>> realized
>> > that the lower portion (at the base of a large tree and a small
>> embankment)
>> > gets swallowed up by snow and ice after the first storm and stays like
>> that
>> > until spring.
>> Snow won't hurt, it's just a nuisance.
>>
>> IF the conduit maintains a grade all the way it won't fill up with water
>> and freeze.
>> This part I'm afraid to ask. What did you use to block the end in the
>> yard to prevent "critters" from turning it into a ready made home?
>> Critters that just love to chew on coax and rotator cables. If you use
>> foam you need to put in a small drain hose so condensation will not
>> collect. Steel wool works great where it stays dry, but not out in the
>> elements. Fiberglass insulation works for some, but some mice appear to
>> not be bothered by it.
>> > After the lines emerge from the conduit they just run over top of the
>> ground
>> > to their respective antennae. After a coax failure to my loop, I tried
>> > pushing a fish-tape through the conduit in hopes of running a new
>> > length
>> of
>> > cable but it became obvious that the inside of this conduit had gotten
>> ice
>> > or muck inside, so I need to wait until spring to try and remedy
>> > things.
>> If there are more than a few cables in the conduit and/or it's a long
>> run it'll be very difficult to push a fish tape through it once it has
>> cables in place.
>> If you did not include a pull or messenger cable in the conduit you may
>> have a problem. You did say that one coax failed so you could use that
>> as a messenger or pull cable to pull in a real messenger. When you
>> finish make sure there is a cable in there that you can use to pull in
>> additional cables if needed. I use a cable/rope length a bit more than
>> twice the length of the run. That lets me make a pull and then pull the
>> rope back for another one while always having a messenger in the conduit.
>>
>> Here are a few of the methods I've used to a tower. You could mount a
>> box on a wood fence post just as well.
>> the conduit has some small (1/8") holes drilled in the bottom near the
>> base of the tower and near where it turns up to go into the box on the
>> house. http://www.rogerhalstead.com/ham_files/cablebox.htm
>> > This now leads to a few much broader questions.
>> > 1) Can I do anything to improve the drainage of the existing 4" conduit
>> > (remember, it's already on a downward angle)? Digging up the back yard
>> > is
>> > NOT an option.
>> How deep is it. With cables in the answer is probably not. If the
>> conduit is "always" on a grade with no low spots it should not need any
>> more drainage.
>>
>> You could build a box for the cables to exit into at the end of the
>> conduit. Put some plastic mesh in it along with a few mothballs to
>> discourage critters. BTW Yellowjackets (Nasty tempered little members
>> of the wasp family) also like places like that conduit or a box at the
>> end.
>> > 2) The coax/control-cables lying on the ground will need to be buried.
>> Do you mean the ones coming out of the current conduit?
>> > That
>> > ground doesn't slope at all, and it fact undulates slightly. How can I
>> put
>> > in conduit for this run that drains properly and won't allow ice
>> > buildup?
>> Have you considered "direct bury" cables? Or something rugged like
>> Davis BuryFlex(TM) and just leave it on the surface or buried shallow?
>> > 3) Does it matter if I use white drainage PVC pipe or grey electric
>> conduit
>> > (all low-voltage)?
>> Not really.
>> > 4) Anything that I haven't mentioned here that I should consider doing,
>> or
>> > potential gotchas?
>> Critters using the conduit for a home and a messenger cable!
>> > Thanks in advance!
>> >
>> Good luck es 73.
>>
>> Roger (K8RI)
>>
>> > ---------------------------------------------
>> > 73 and Good DX
>> >
>> > Peter,
>> > W2IRT
>>
>>
>> _______________________________________________
>>
>>
>>
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>
>
>
> --
> Jim K0XU
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