[TowerTalk] water in EMT conduit

[Grant Saviers]

"Hermetic" is very difficult to do.   Belden withdrew their air 
dielectric RG8 series coax because of water migration (original 9913 not 
current 9913F7).  I know, I had 270' of it in a conduit. Consider also 
the perm ratings of the plastic covering, water vapor can migrate 
through some of them.  I bought some 9913F7 when Buryflex was out of 
stock and regret it.  Direct burial rated coax and cables are best for 
any buried conduit.

I've also built some deflagration test chambers and stranded wire can't 
be used in any seals as the leakage in between the strands is too much.

Grant KZ1W


On 2/27/2013 2:09 PM, TexasRF at aol.com wrote:
> 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 at 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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