Re: Harsh Environment Cat5?

James Knott wrote:

> J. Clarke wrote:
>
>> Only if it was crap to begin with. The electric power cabling in my
>> house has not hardened or cracked in more than 30 years, and the cable in
>> my parents house was fine last time I looked at it, at which point it had
>> been in place for over 50.
>>
>> The conductor may corrode but without UV exposure the insulation on any
>> cable that meets any reasonable electrical code will not "harden and
>> crack" in just a few decades.
>>
>> If there is UV exposure then you should be using a cable rated for such
>> use.
>
> I've seen decades old power wire insulation that's crumbling.

How old, and what kind of plastic was used? If you go back far enough then
there is no plastic of any kind in the insulation--it's varnished cambric.
That in general _is_ crumbling now. After that rubber was used--it also is
crumbling now. Some of the early plastics may not be holding up either.
But any wire installed in a building in the US that is less than 4 decades
old that is "crumbling" is just plain _crap_ that should never have passed
inspection.

> The aging
> of plastic is a fact, in that the plasticizers that make it flexible,
> evaporate with time, even without UV. As an example, take a look at some
> food storage containers that are a few years old.

So? It appears to have escaped your notice that there are many kinds of
plastic and the kind from which food storage containers are made is
generally not the kind used to insulate electrical wiring.

> They're not as flexible
> as they were originally and will eventually crack.

This is true for some kinds of plastic but not for all. The hardening
mechanism is usually crosslinking, not "evaporation of plasticizers" and
the reason that UV accelerates aging of plastics is that it increases the
rate of crosslinking. Most modern electrical insulation is already heavily
crosslinked, so that ceases to be an issue.

Now, please explain to me why I can take a piece of wire installed in a
house in 1968, more than three decades ago, and bend it back and forth
until the copper inside the insulation work-hardens and breaks, without any
cracks or any other kind of indication of failure appearing in the
insulation, if such insulation will "crumble" in "decades".

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)
.

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