On 2/7/2011 9:00 PM, Sam Andrews wrote:
> 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.
Yes
> 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.
I go up to 75%, but "use lots of WIRE SOAP"
http://www.rogerhalstead.com/ham_files/cablebox.htm and use a messenger
of sufficient size. Far too often messenger cables are too small and
can exert stress on the conduit, or even cut into the inside of bends.
If you have a small messenger cable, use it to pull in a larger one and
use that to pull in the additional coax. (USE LOTS of wire soap!) See
last photo on the above link. Note the foam in the one fitting. That
is the back end of an open stub that sticks down about a foot and is
designed to keep critters (bees and wasps) out.
> 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.
Use a series of *small* holes drilled into the bottom of the conduit
and make sure the conduit is in soil that will aid drainage. Larger
holes can snag coax being pulled in or offer a route for burrowing critters.
> 4. Never use PVC bends or elbows (45-degree or 90-degree) below grade.
I use a pair of sweep 45s instead of a 90 and have never had a problem.
OTOH the largest coax has been LMR 600 and the run is about 120 feet.
So I'm pulling through three 90s (two vertical and one horizontal) with
little resistance. Although it sounds counter intuitive, it's easier to
make one large pull instead of two or three smaller ones.(and use LOTS
of WIRE SOAP) The shorter run is only about 60' with two composite 90s
(made of two sweep 45s)
> 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.
>
A couple points about using larger PVC conduit and steel for that matter.
With PVC it's essential that the male section of each junction is FULLY
SEATED into the next section. If not fully seated it will form a squared
off edge of 1/4 to nearly 3/8"" on which cables can catch on and it's
difficult to get them all pointed the same direction. If need be, bevel
the inside of the male end to a 60 degree angle so there is no lip to
snag the coax. AND USE LOTS of WIRE SOAP!
I use enough conduit so all the joints are under pressure even in cold
weather. The last two runs I greased with DC-4 compound instead of using
PVC glue. They are still water proof and allow the joint to fully seat
and the conduit can be reused. Without either the lube or glue it's
almost impossible to make a proper joint that is fully seated. This
gives a run with a relatively smooth interior which aids in pulling
cable...along with LOTS of WIRE SOAP!
Using steel 45s and 90s. A 90 puts a LOT of strain on the coax being
pulled and the interior of the conduit is quite rough so a pair of sweep
L's reduce the drag and abrasive force on the coax jacket. Carefully
DE-BURR the ends of the conduit as a tiny burr can peel the jacket right
off a piece of coax. Leave no rough edges that can contact the coax.
So, good luck and DONT forget the WIRE SOAP! (It's cheap, be generous
with the application)
73
Roger (K8RI) (Did I remember to mention WIRE SOAP?)
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