(I'm happy that you live in such a nice dry place but I guarantee every one
of my conduit's here are full of water. This is SC and the humidly here for
months on end will run 90 to 100%. In the field we use to pull a jackhammer
compressor behind us to blow the water out of street conduits when I worked
in the street crews. I believe I know where the issue come from. Years ago
the ARRL handbook had a diagram of how to drain your conduits. I have no
clue why they considered it importance but I have some 30 year old TRW on
the roll and not THHN that still water resistance to this day. I think it
far more importance to keep the water out of our radio's than underground
lines. I' feel for the poor people who was hit in OK as I seen Grand Rapid
NE in the 70's after it was hit. It not like a hurricane where you have time
to run. 73 and a safe holiday. Gene AA4VX
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
Patrick Greenlee
Sent: Saturday, May 25, 2013 11:25 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Need Help For Cable Runs To Tower
How high is up?, how long is a roll of string? These are two easy questions
compared to the knock down drag out fights we have had over conduit, holes
for drainage or no holes...
I have successfully glued PVC pipe that survived 100 plus PSI keeping water
in and believe a good job on plastic conduit will keep water out. It is
possible that if you don't seal the conduit well at the ends (I like GE
Silicone rubber, the 50 year kind with no vinegar smell when curing) that
over time condensation will potentially build up (maybe in Biloxi,
Mississippi) but less likely in dry parts of California. I have a strong
cord run through all of my conduits and can tie it into a continuous loop
whenever I want. This is good for pulling a dry rag through the conduit to
test for water. So far no water after a few years.
If I had a recurring condensation problem I could arrange for a periodic
leak of dry air to be injected into the conduit as I have a refrigeration
unit type air dryer on my shop air system. There are commercially available
dehumidifier chemicals that could be used to absorb moisture. The
silica-gel type can be recycled by heating in the oven over and over and
don't "wear out."
My advice (risking being flamed...) is to do a good glue job plus seal the
openings. If you opt for a desiccant, install "T" fittings so you don't
have to reseal the ends with RTV every time you change the gel pak(s). Long
run? Consider a "T" with a "riser" at intermediate distance(s.)
Note: Two conduits does not imply two failures to get a short since the
wires will be insulated. You would need both wires to lose their insulation
plus both conduits to fail and then a miracle migration of the wires so they
could touch. Of course if you are a member of the drain hole camp and
insist that bugs will sneeze into the conduit with sufficient force to get
past the RTV then wire migration say during an earthquake could be a
problem if the tower is still standing.
Disclaimer: I acknowledge that some folks have had water ingress into their
conduit, that it is not a laughing matter, and that minor misinterpretations
of the laws of physics are the likely root of the mistaken ideas propagated
post water incident/disaster. ;) ;)
Patrick AF5CK
P.S. I am still working on taking down the 40 ft tower made of 4 1/2 inch
tubing with 14 ft between the triangular legs at ground level. For those of
you who have heard about some of our "interesting" weather you can
understand a certain lack of alacrity in finishing that project. (I'm about
25 miles from ground zero of the latest Oklahoma tornados and the tower is
closer. I was dong some prepping Sunday the day of the Shawnee twister and
drove through the devastated area a couple hours before the devastation took
place totally unaware of what was to come.
-----Original Message-----
From: Jim Lux
Sent: Saturday, May 25, 2013 3:57 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Need Help For Cable Runs To Tower
On 5/25/13 1:02 PM, Eugene Jensen wrote:
> Drilling holes in conduit for drainage is not a good ideal. It going
> to be full of water in time. As long as your trench is 18 " or deeper
> you could use UF #6-2 with ground to keep the voltage drop under 3%.
> And the run your control/Rf cables in the same conduit, It you using
> hard line just bury it in the trench. 73 and good luck with your tower
> project. Gene AA4VX
>
CHeck your local codes, if you're concerned. around here (Thousand Oaks), UF
is not allowed for direct burial. Underground has to be in a raceway (code
speak for conduit). There's various burial depths depending on the kind of
conduit (plastic, thinwall metal (EMT), or thick wall metal) and whether
it's under a concrete slab or similar.
The depth is all about damage to the wires (since frost is a non issue).
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