Much of the outdoor wire dielectric won't change much with age. If
you're looking at the really old rubber stuff you'll get a lot of change
since that material degrades over time. The newer stuff tends to be
polyethylene-based which holds up *very* well over time.
The C Rural wire that's been discussed (looks like huge zip cord, CCS
wires, etc.) I looked up -- it uses high-density polyethylene
insulation. I would expect that that wire's insulation properties will
change *very little* over time. I know we expect a useful life for
polyethylene-jacked fiber optic cables of 20-30 years and I would expect
that the C Rural wire would have similar expected useful life (and in
practice it should last a lot longer than that). Note also that the spec
for this wire is 14 or 12 gauge conductors (there are two options listed
in General Cable's catalog), both are specced for 30% copper content.
Also, someone on here had corrected me for talking about an older
version of "C Rural wire" that was oval and used rubber insulation. I
looked that up too (Drop Wire), and it is similar but definitely not the
same (I've only run into it one or two times so I don't have as much
experience with it), so I was mistaken referring to it as an "older
version" of the C Rural wire. It is listed as 18.5 gauge CCS conductors
and PVC insulation. It also lists 30% copper content in the conductors.
I've only ever seen this in an old version that appeared to have rubber,
rather than PVC, insulation. It lasts a long time but it's properties
aren't as good for our antenna applications as the C Rural wire.
Regarding the smell and "curing over time": plastics should generally
not "cure over time". Some plastics (notably flexible PVC) tend to be
modified with plasticizers to make them more flexible and those can
migrate out over time. The result after aging is a stiffer, and more
prone to cracking, cable. This isn't curing, it's just aging and is the
primary reason why those types of cables have a much shorter useful
life. Plastics like polyethylene are usually used in their natural state
(which tends to result in stiffer cables), and they generally last much
longer without noticeable degradation. The main enemy of
polyethylene-jacketed cables is ultraviolet light which is why the
cables are black (the black pigment is a UV inhibitor that protects the
polymer in the cable jacket). I have some cables in our system at work
that have been in the air, in full sun, for around 10-15 years now and
the jacket gets a chalky look to it but is completely fine and even
"feels" OK when subjected to the "scratch it with your fingernail" test.
If you use the telco-type wire for your outdoor runs you'll be amazed
how long it lasts.
-Bill
> Yeah, so he says when the wire is new. There is an ASSUMPTION that
stuff
> retains characteristic at RF over time when it was only designed for
> audio.
>
> Have you ever noticed how pungent that stuff smells when you first
pull it
> off the roll. That stuff cures over time. Guys at Bell Labs had HUGE
> fields planted with thousands of telephone poles, different wood,
> different
> treatment, some in ground for decades and decades, TESTING real life
> deterioration.
>
> Some of that wire has been in the air since before I was born,
carrying
> audio. That's what it was made for, tested for, certified for.
>
> Maybe if Herb still has it, he can run a test on the strung out,
"aged"
> wire with a 450 ohm resistor on the far end of it, and get char
> impedance,
> loss and velocity factor numbers on it. It's been out there in the
salt
> air for a while now.
>
> Herb???
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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