[TowerTalk] another subject: coax and cables buried or elevated above ground?

[Al Kozakiewicz]

QST is not peer reviewed.  All kinds of nonsense can make its way into print.

The notion of copious condensation in buried conduit has always seemed like ham urban legend to me. 

First off, there are literally millions of miles of buried electrical conduit in the world filled with wire not rated for immersion. The failure rate for this infrastructure does not seem to be anything exceptional.

More important, condensation requires a constant supply of moist air. Where is this supply coming from? Not convection, unless someone changed the laws of physics while I wasn't looking. If there really is enough air flow from the pressure difference between the ends of the conduit sufficient to bring in the required moisture (unlikely), then seal the ends. Simple.

Al
AB2ZY

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From: TowerTalk <towertalk-bounces at contesting.com> on behalf of StellarCAT <rxdesign at ssvecnet.com>
Sent: Thursday, January 28, 2016 8:22 AM
To: tower
Subject: [TowerTalk] another subject: coax and cables buried or elevated        above ground?

My ongoing tower/antenna projects... hopefully I’m not boring others out there...

I had planned on burying all lines to the towers (2, one at 150’ out and one at 300’ out) ... at first I thought in solid joined (sealed) PVC which I can get for $9/10’ ... and I’ve also thought about direct burial which for the coax and control cables has the added benefit of increased capacitance to ground and thus a reduction of energy (lightening event) that reaches the shack... but control cables aren’t normally rated for direct burial... or at least I don’t think so (researching that now)...

Then this latest QST article on coax says DON’T bury in any type of conduit be it plastic or otherwise. It says condensation WILL get inside and ruin (flood) the cables.

So .... if the cables are underground – below the frost line – say minimum 1’ down (upstate SC) ... how will condensation develop? Or will it? I’m an engineer (HW/SW development) and reasonably intelligent but find it difficult to wrap my head around this issue... will it or won’t it – flood that is? if it were always under ground – including both ends then I’d think not.... but it isn’t always under as the ends come up to and above the surface... does that introduce a temperature variant enough to induce condensation? And I don’t like the idea of holes in the plastic – that just means mud will indeed eventually work its way inside.

Maybe use corrugated tubing (again – no cuts or openings) ... this would allow whatever moisture there might be, and I can’t imagine its going to be a great deal, to settle in the lower points of the corrugation.

Comments from others that have been through this - in the south with similar conditions would be appreciated.

Alternatively I could use a leader line and go from say 15’ on the first tower to the second tower and then that same level to the shack with supporting 4x4 poles along the way... but this seems iffy as well as first the cables are ‘leaving’ the tower above ground potential so that might mean a higher voltage (common mode – probably?) on the lines (again: lightening type event)... and the first tower is a rotating tower ... although thinking about it that might work quite well to go from the tower with a ‘swing-arm’ of hanging coax/cables to allow rotation.

thoughts?

Gary
K9RX
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