[TowerTalk] Double Coax Runs to Reduce Loss

[john at kk9a.com]

I used heavy THHN for rotator wire and it holds up fine outdoors.  As you
said the exterior clear coating peels off put the PVC does not seem to
degrade.

John KK9A

To:	Jim Thomson <jim.thom at telus.net>, towertalk at contesting.com
Subject:	Re: [TowerTalk] Double Coax Runs to Reduce Loss
From:	Grant Saviers <grants2 at pacbell.net>
Date:	Fri, 23 Dec 2016 10:01:48 -0800

Why THHN insulated Cu wire would abnormally degrade vs other Cu wires is a
bit of a mystery to me. Yes, the nylon exterior will severely degrade after
a couple of years in the sun from UV, but the PVC layer is the same as every
other PVC insulated wire and will slowly degrade also unless a UV resistant
grade which just takes longer. Re the "insulation carrying RF current" of
course it is in the RF field, just put the correct numbers for thickness and
dielectric constant into NEC/EZNEC to see the effect. I use the thickness
weighted average of the nylon and PVC constants as a reasonable guess (3).
Other TTer's can probably provide better and more detailed ways to analyze
the dielectric constant and losses.

There are many specs that apply to electrical service. ASTM B49 for the
copper is constant for all insulation systems including none. Federal
A-A-59544 & 59551, UL83 and many more if you are willing to pay for them.
The Fed specs are free. Of course anything is possible for out of spec
alloys, China Cu over Al wires, 14 ga that is really 18ga, etc.

THHN is only approved for dry locations, but that is for electrical service
to 600v. Does that matter for radials? I think not. Just consider the losses
of earth burial, overwhelming compared to a few thou of insulation.

Grant KZ1W