[TowerTalk] THHN wire problem

[Hardy Landskov]

All,
Thought I would jump in and tell you my tale of woe about using THHN
insulated wire.
I bought a 1000 ft roll of  #12 copper from Home Depot to make some 160
meter radials. After about 2 years, the insulation had turned hard and was
cracking. When I peeled back some of the insulation from one of the wire
ends, the wire had a greenish sticky substance all over it. I asked N7IR
who is fairly knowledgable in chemistry and he said the insulation
outgasses a substance that attacks the copper. Wish I could remember
exactly what he said it was.
With that info, I immediately took down all the radials and stripped off
all the insulation. They were a real mess. The wire cleaned up nicely using
a soapy type of brillo pad and a garden hose.
Out here in AZ practically nothing lasts in the heat and ultra violet we
have. I was happy to catch the problem before it got worse. Of course, YMMV.
73 N7RT

At 10:27 PM 10/22/2007 -0700, Jim Brown wrote:
>On Mon, 22 Oct 2007 19:06:40 -0400 (EDT), n8cc at mei.net wrote:
>
>>Faced with this question several years ago, I made a 15 meter dipole
>>out of #14 solid copper 600V THHN wire.  I strung it up between a
>>tree and  a wooden pole, about 20 feet off the ground.  I checked
>>the resonant frequency.  I then lowered the antenna, stripped  the
>>insulation off the wire, and repeated the exercise.  The difference
>>in resonant frequency was almost exactly 3 percent.  Since then,
>>I've observed that THHN wire always makes a difference of between
>>2-3 percent from formula, depending on wire size,manufacturer, and
>>whether solid or stranded.
>
>>Not the most scientific approach, 
>
>I'd call that VERY scientific -- you set up a controlled experiment and 
>carefully measured it! The only way to improve your science would be to 
>measure a lot of antennas and a lot of wire types and wire sizes. But 
>what you've done was right on, and quite helpful! Thanks. 
>
>73,
>
>Jim K9YC
>
>
>
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