[TowerTalk] [Bulk] Fwd: where the condensation comes from

[Grant Saviers]

Yes, stop the flow to reduce the ongoing collection of moisture, and a 
corollary could be:

If it is hot and humid outside, you probably are running the AC which 
lowers the wet bulb below outdoor air WB.

If it is cold outside, the RH will be lower inside a heated structure 
but the wet bulb may be higher or lower than outside - condensation on 
window frames is a sure sign that interior wet bulb is higher than 
outside air temperature.

What matters most is the temperature of the buried conduit vs the wet 
bulb of the air entering the conduit.

One end plugged stops the flow, and both ends plugged are usually not 
hermetic so changing atmospheric pressure brings in moisture. (in trying 
to make gas pressure seals, I found it surprising how much flow goes 
down inside regular stranded wire).

So, plugging the outside end of the conduit and leaving the inside end 
open is maybe sometimes possibly better than both ends plugged.

IMO, the only "sure thing" for a dry conduit is a low flow or slight 
pressurization of very dry air.  Since both ends of my conduits are 
outside, I use direct burial cables and don't worry about condensation.  
In fact, a plus of condensation is it keeps the wire pulling lubricant 
active, so removing cables/coax is much easier. Nice when I was 
salvaging about a thousand feet of LDF4 and LDF5 from conduit with 
condensation.

Grant KZ1W



On 1/31/2016 8:01 AM, Hans Hammarquist via TowerTalk wrote:
> So, what Jim is stating is:"Avoid ventilation of the duct as much as possible regardless openings up or down."
>
>
> Hans - N2JFS
>
>
>
> -----Original Message-----
> From: Roger (K8RI) on TT<K8RI-on-TowerTalk at tm.net>
> To: towertalk<towertalk at contesting.com>
> Sent: Sun, Jan 31, 2016 12:43 am
> Subject: Re: [TowerTalk] where the condensation comes from
>
> In the summer here 85%, or more at 80 to over 90F is not uncommon.  So
> that's a lot more water, but the outside ends of the conduit are inside
> sealed NEMA boxes. The coax comes out at the tower, either through
> bulkhead connector or fittings that seal against the coax jackets or
> control cables. The same at the house and shop ends.
> Depending on open conduit ends (assuming they point down) and wind
> direction, the wind can cause pressure or suction from blowing across
> the open end.
>
> 73
>
> Roger (K8RI)
>
> On 1/30/2016 Saturday 8:35 PM, jimlux wrote:
>> I did a bit of calculating about what might push damp air into a conduit.
>>
>> I assumed that I had 30 meters (100ft) of a 2" diameter tube where
>> there was a pressure difference corresponding to a 10 mi/hr wind (it's
>> about 1/4 lb/sq ft)
>>
>> You'd get a flow of about 2 liters/second (which is surprisingly high)
>>
>> In an hour, then you'd have 7200 liters.  If you had 100% humidity air
>> at 68F (20C) going in, and the soil was at 50F (10C), you'd be
>> condensing out about 50 grams/hour.
>>
>> In reality, you probably don't have 100% humidity at 68F. But you
>> might have 50% humidity at 85F, and that's about the same amount of
>> water.
>>
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