[TowerTalk] Pulling coax through PVC pipe

Patrick Greenlee patrick_g at windstream.net
Wed Jan 31 08:54:35 EST 2018

Different strokes... Some, like Chick, vent underground conduit to the 
surface air, others put drain holes in the underside, some try to seal 
it up (with or without desiccant), others purge with "dry" air 
intermittently or warm dry air continuously, others may get good results 
doing nothing extra, and so on and so forth  A N D  most say "it works 
for me." There probably is no single best answer, certainly with the 
wide variety of climates.  In some places if you tried drain holes the 
ground water would flood your conduit.  Some places venting to surface 
air will allow condensation in the vent pipes as temps and RH go through 
the diurnal cycle adding water to your buried conduit over time.

If the conduit is sealed well one of the few ways for moisture to gain 
entry is via poorly sealed coax.  Moisture can egress via the shield of 
improperly sealed coax. I did nothing "heroic", just installed my 
various PVC conduits with plenty glue, a twist, and hold fully engaged 
for 30 sec to get a proper glued joint.  When going back to a previously 
wired conduit to add more wires I never detected any moisture. I guess 
I'm lucky to be fortunate enough to have benighn conditions that don't 
require special amelioration.

One glaring oops in my conduit experiences is the last 4 inch S&D run 
which is a minor embarrassment in that during backfilling I got lazy and 
too hurried in backfilling and ended up with rocks and large hard clods 
in the backfill against the conduit which when driven over damaged the 
conduit. How do I know the conduit was damaged? Ground water entered the 
conduit which was on a slope which made a considerable head of pressure 
and over flowed the terminal end of the conduit which was 2 ft above my 
barn floor. Water poured out onto the slab at a rate of several gallons 
per minute.  I used a cordless 4 1/2 inch angle grinder to cut a relief 
hole just above grade outside of the building so the water stays out 
side the building.

Now what to do to salvage the situation, preferably without replacing 
the conduit.  Local big box stores sell rolls of 1" flexible irrigation 
pipe rated at 100PSI for $12.  I pulled my wires and cables into some of 
these, sealed the ends super water tight and then pulled those through 
the flooded conduit.

My cables are still in the PVC conduit and so protected from the evil 
cable munching critters we have that delight in chewing on direct bury 
cables  A N D  they are protected from water up to 100 PSI (not likely 
to  be a problem.) The best part was not digging up and replacing the 
conduit.  A side benefit is that additional wires could be placed inside 
another run of 1 inch irrigation tubing and easily pulled along current 
cables as the irrigation tubing gives you a smooth non-snagging pulling 

Hopefully none of you TowerTalkers will need to use my remedy but there 
it is, just in case.

Patrick        NJ5G

On 1/30/2018 4:02 PM, Chick Allen via TowerTalk wrote:
> One thing to consider that will mitigate the "wet location" issue is to vent the conduit with some vents installed along the conduit.  This is done using a simple pvc "tee".  If you're using 2" pvc, just connect the lengths at several different points with a 2"x2"x2" tee, reduce the vertical tee to something smaller, like 1" or 3/4" and bring that about one foot above the ground.  There you can add a sweep el that will prevent moisture from entering the conduit while allowing condensation to evaporate.  Plan your above ground vents around a fence post or some other above ground object so it won't get broken as easily.  Otherwise, a short piece of treated 4"x4" will provide a stable support.  Works for me.
> 73 de Chick / NW3Y
> -----Original Message-----
> From: Shane Youhouse <kd6vxi at gmail.com>
> To: towertalk <towertalk at contesting.com>
> Sent: Tue, Jan 30, 2018 2:34 pm
> Subject: [TowerTalk] Pulling coax through PVC pipe
> I wouldn't be so quick to run ANY romex through PVC when it's buried.  It's
> against code.
> Article 300 of the NEC states any buried pipe is considered a wet location.
> *300.5 Underground Installations.*
> *(B) Wet Locations.* The interior of enclosures or raceways installed
> underground shall be considered to be a wet location. Insulated conductors
> and cables installed in these enclosures or raceways in underground
> installations shall be listed for use in wet locations and shall comply
> with 310.10(C). Any connections or splices in an underground installation
> shall be approved for wet locations.
> Then, article 334 implicitly states you may NOT use romex (NM) in damp
> locations.
> *334.12 Uses Not Permitted.*
> *(B) Types NM and NMS*. Types NM and NMS cables shall not be used under the
> following conditions or in the following locations:
> (4) In wet or damp locations
> As such, you are MUCH better off running single runs of wire in addition to
> a heavy ground to keep SPG intact
> There are a LOT more rules regarding NM style wiring, but this is the gist.
> Also, it's not always wrong to mix 120 volt and low voltage.  As long as
> you use THHN or other 600 volt insulation and all wiring is class 1, you're
> OK.
> --Shane
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