Patrick, the problem here is that it is not possible with the usual
materials available to hermetically seal the conduit on the ends where the
wiring
enters and exits.
If it were possible, then one would do that while there was a positive
pressure inside the conduit and all would be fine.
Theoretically a hermetic seal can be done. Practically, it can't be done.
The small amount of water vapor present in the also small air exchange from
heat/cool cycles is a source of condensation. True, only a little day by
day but over time it accumulates and that is the problem.
This problem is so insidious that it can happen inside a hollow coax center
conductor and accumulate inside the coax connector. In North Texas, in the
Fall of the year, several droplets of water can accumulate in a couple of
weeks.Cable manufacturers now offer rubber "bullets" to install inside
hollow center conductors to stop the flow of vapor laden air and water
condensation. This is as close to a hermetic seal as one can hope for.
73,
Gerald K5GW
In a message dated 2/27/2013 1:55:30 P.M. Pacific Standard Time,
patrick_g@windstream.net writes:
Lets see if I followed the gist of the thread...
If a conduit with no water in it is hermetically sealed it will promote
condensation.
Conduits should be left open so they can dry out.
Sealed conduits will breathe with changes in temp and barometric pressure
and thus admit moisture.
...and so on and so forth...
********************************************************
I'm still wondering how a conduit properly installed and sealed admits
more
and more moisture over time. Ideas? (Porosity of PVC increased by
electromagnetic forces, intervention by space aliens, or what?)
I can't help going back to the question of how PVC pipe that can hold over
100 PSI successfully without any leaks, when partially filled with cables,
can't withstand changes in ambient pressure rarely reaching or exceeding
5PSI. Max swings in barometric pressure from high pressure weather
phenomena
to lows of cyclones shouldn't exceed this level much if at all. Excluding
critters and sealing the end of the conduit can be as simple as drilling
nicely fitting holes in an inexpensive PVC pipe cap to let the wires exit
and sealing the wire/hole interstices with silicone rubber or Excel. If
you
want to go to Herculean lengths then bulkhead feed through fittings with
rubber stoppers of compression sealing design will surpass the
requirements.
Patrick AF5CK
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