Topics

Buried Conduit


Mark Brueggemann
 

Since it's been mentioned I've been wondering, is any consideration for condensate or water ingress made for buried conduit with coax in it?  I'm thinking even vented with a "candy cane" any moisture that might get in there would be a long time evaporating, if it ever evaporated at all.  It also assumes all joints are glued perfect.  So does one just assume any lines in there will be partially or completely submerged for some part of that length or is the nominal venting they have sufficient to keep things dry?

Mark K5LXP
Albuquerque, NM


Mike Allred
 

It is worth some thought.

Some say that they have never had issues with water in their conduit.  It may be a matter of climate.  I live in a humid area of the country.  I can tell you that all utilities in the area that use underground conduit (CATV, telephone) use pretty extreme methods to keep moisture out including jelly filled cable and pressurized air flow throughout the length of the conduit.

Below is a snip from QST:

"Regarding the burial of coax, I would suggest being very careful of how you install your PVC. The problem is that a horizontal run of PVC will tend to accumulate condensation with the result that the coax will eventually be at least partly submerged. Direct burial-rated coax is designed to be buried in soil, not submerged - that takes submarine-rated cable, likely beyond most hams' budgets.

If you do use PVC to protect your coax, I suggest you use pipe with drain holes along the bottom, or with pitch and a port so that water can drain out on the low end. Especially with clay or hard soil, I would provide drainage into sand and then crushed stone either at a pit at the drain end, or along the length of perforated pipe. If you do one of those things, it should be fine."

(Hallas, Joel R., W1ZR. "The Doctor is In." QST, Nov. 2016, p. 72)

I dug a small pit at the low end of my conduit and lined it with landscaping fabric.  Then I filled it with crushed stone and drilled multiple small holes in the bottom of the conduit at that location.


Mike

ps. In the same article the author has interesting comments on common mode chokes and verticals.  Worth checking out.

---- On Fri, 04 Sep 2020 11:37:18 -0500 Mark Brueggemann via groups.io <qrq_cw=yahoo.com@groups.io> wrote ----

Since it's been mentioned I've been wondering, is any consideration for condensate or water ingress made for buried conduit with coax in it?  I'm thinking even vented with a "candy cane" any moisture that might get in there would be a long time evaporating, if it ever evaporated at all.  It also assumes all joints are glued perfect.  So does one just assume any lines in there will be partially or completely submerged for some part of that length or is the nominal venting they have sufficient to keep things dry?

Mark K5LXP
Albuquerque, NM






Tim N8NEU
 

Would a trap similar to gas lines work to drain water out of a conduit? Perhaps put the water drain trap at the the bottom of the candy cane or low point of the conduit being bent to come verticle.

I would think filling the open end of the candy cane and coax with a tar like puddy and then adding liquid tape would keep out rain water blown by the wind. 
 
I was thinking of putting the coax in the conduit before sealing the conduit connections. Adding liquid tape after sealing the conduit connectors would add an extra layer of water proof sealant.  

I was going to do this above ground. After all sealing is complete, then lay the conduit in the trench already dug.

I'm just throwing out some ideas. Others may have already solved this issue.

73

Tim - N8NEU
FN00ah



-------- Original message --------
From: Mike Allred <mike@...>
Date: 9/4/20 13:22 (GMT-05:00)
To: Butternut <Butternut@groups.io>
Subject: Re: [butternut] Buried Conduit

It is worth some thought.

Some say that they have never had issues with water in their conduit.  It may be a matter of climate.  I live in a humid area of the country.  I can tell you that all utilities in the area that use underground conduit (CATV, telephone) use pretty extreme methods to keep moisture out including jelly filled cable and pressurized air flow throughout the length of the conduit.

Below is a snip from QST:

"Regarding the burial of coax, I would suggest being very careful of how you install your PVC. The problem is that a horizontal run of PVC will tend to accumulate condensation with the result that the coax will eventually be at least partly submerged. Direct burial-rated coax is designed to be buried in soil, not submerged - that takes submarine-rated cable, likely beyond most hams' budgets.

If you do use PVC to protect your coax, I suggest you use pipe with drain holes along the bottom, or with pitch and a port so that water can drain out on the low end. Especially with clay or hard soil, I would provide drainage into sand and then crushed stone either at a pit at the drain end, or along the length of perforated pipe. If you do one of those things, it should be fine."

(Hallas, Joel R., W1ZR. "The Doctor is In." QST, Nov. 2016, p. 72)

I dug a small pit at the low end of my conduit and lined it with landscaping fabric.  Then I filled it with crushed stone and drilled multiple small holes in the bottom of the conduit at that location.


Mike

ps. In the same article the author has interesting comments on common mode chokes and verticals.  Worth checking out.

---- On Fri, 04 Sep 2020 11:37:18 -0500 Mark Brueggemann via groups.io <qrq_cw=yahoo.com@groups.io> wrote ----

Since it's been mentioned I've been wondering, is any consideration for condensate or water ingress made for buried conduit with coax in it?  I'm thinking even vented with a "candy cane" any moisture that might get in there would be a long time evaporating, if it ever evaporated at all.  It also assumes all joints are glued perfect.  So does one just assume any lines in there will be partially or completely submerged for some part of that length or is the nominal venting they have sufficient to keep things dry?

Mark K5LXP
Albuquerque, NM






 

Tim,
The heat and cold cause the conduit to breathe and that is what brings in a lot of the moisture.  Sealing it won't do much when you have those extremes.  I really should use the wet vac and see if I can draw any water out now that I am thinking about it.
Al

--
Al
WB9UVJ


Al AB2ZY
 

This quote repeats the common ham myth that condensation in conduit is an issue. The cure suggested is akin to drilling holes in the bottom of a boat to let out any water that gets in. It overestimates the amount of moisture contained in air and totally ignores the physical principles that drive convection.

As I have repeated many times elsewhere, there are millions of miles of buried conduit uninstalled in the world. Condensation is just not a problem in 99.999% of those miles.

Al
AB2ZY


Mike Allred
 

The author of the article has undergrad and graduate degrees in Electrical Engineering and was a professor.  I don't know him, but that sounds like someone that knows how to evaluate information sources and not perpetuate myths.

I'll write him and see if he has any sources he can cite for his comments.

Will report back to this group if I receive a reply.


Mike


---- On Sat, 05 Sep 2020 09:19:12 -0500 Al AB2ZY <akozak@...> wrote ----

This quote repeats the common ham myth that condensation in conduit is an issue. The cure suggested is akin to drilling holes in the bottom of a boat to let out any water that gets in. It overestimates the amount of moisture contained in air and totally ignores the physical principles that drive convection.

As I have repeated many times elsewhere, there are millions of miles of buried conduit uninstalled in the world. Condensation is just not a problem in 99.999% of those miles.

Al
AB2ZY






Al AB2ZY
 
Edited

I know how to evaluate information as well. The weight of the water (90F, saturated assumed) in volume of air equivalent to 100' of 2" conduit is 0.177 lbs. 1/4 cup approximately according to the table I looked at, and that assumes all of the vapor condenses out upon cooling, which it doesn't. . Convection works by warm air rising, cold air sinking, not the other way around. Warm air is capable of holding more moisture than cold air. so assuming that you can get convection in a buried pipe when the air within is warmer than the atmospheric temperature, you are introducing drier air, not moister.

Water in buried conduit primarily comes via ingress from open ends exposed to elements, or leaks from fractures or bad joints and the hydro-static pressure of ground water.  And as any construction apprentice knows, perforated pipe is designed to let water in, not escape.

Al
AB2ZY