Hans, thanks for the pat on the back for Pat.
Why would the corroded layer conduct enough to carry a sizable amount of
current when it is in parallel with good copper? Think of various
resistors connected in parallel. The highest ohm values carry the least
current.
Surely the skin effect doesn't force the insulation to conduct or in the
case of bare wire in contact with the air does the air get "forced" to
conduct by the skin effect and drive up the resultant impedance? Of
course not. There is a continuum of impedances which taken in aggregate
are the presented impedance of a conductor.
If anthropomorphism will help make a point lets visualize sentient
electrons which when given a choice from among the various paths will
tend to choose the path of least resistance making for very little
current flowing in the insulation or the air next to a bare conductor.
Why would these smart electrons choose to avoid the air surrounding a
bare wire and avoid the insulation but flock to a corrosion product of
low conductivity? Don't answer, SKIN EFFECT, as that puppy won't hunt
since if skin effect could do that it would have current flowing in the
insulation or the air in contact with a bare wire.
Wouldn't the current flowing in the various portions of a wire with
surface corrosion exhibit current flow in the corrosion only in
proportion to the inverse of its impedance? Think resistors in
parallel. Does not the current apportion itself by the relative
resistances of the paths such that the low value resistors get the most
current and the really high value resistors get a small portion?
Patrick NJ5G
On 12/28/2016 6:51 PM, Hans Hammarquist via TowerTalk wrote:
I think Partick has a point. Why is the current trying to go through the
insulating top layer of the copper wire.
Now, if you study the skin effect and apply the formulas you will find out that the skin
effect on an insulating layer is very, very deep to the point that hardly any (actually
non to pay attention to) is going via the insulator. Same thing with the oxidized layer
on a bare copper wire. The skin effect "sends" all (almost) to the conducting
copper wire. The only time there might be a problem is if the corroded layer is
conducting enough to carry a sizable amount of current and thereby cause attenuation. I
doubt that the THHN isolation can deteriorate to a conducting phase.
Aluminum wires have the advantage that aluminum oxide is not conducting unlike
copper oxide, the red oxide, is.
Man, this start to be complicated. Better find that North Seeking Owl.
Hans - N2JFS
-----Ursprüngliche Mitteilung-----
Von: Patrick Greenlee <patrick_g@windstream.net>
An: towertalk <towertalk@contesting.com>
Verschickt: Mi, 28 Dez 2016 8:57 am
Betreff: Re: [TowerTalk] UV and WX deterioration of THHN insulation, and effects
Skin effect... If skin effect can force conduction into the outer limit
of the wire (the chemically altered part with poor conductivity) then
why doesn't the skin effect force conduction out into the insulation and
really have poor conduction? (or in bare wire out into the surrounding air)
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