[TowerTalk] UV and WX deterioration of THHN insulation, and effects

[Patrick Greenlee]

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)

My friend and guru (who refuses to post here) has been a ham for several 
decades, is a retired EE, and has 35+ years antenna design experience 
(his specialty) agrees with the concept that RF conductivity can be 
characterized as a collection of parallel impedances, a continuum 
actually.  The depth of penetration of RF in a conductor does not have a 
"magic" cut-off point but instead has an exponential extinction.  That 
is, the deeper into the conductor the less RF but there is no magic 
barrier preventing RF from penetrating to any arbitrary depth, although 
at rapidly reduced values.

Some folks (myself included) often talk about electrical current like it 
was a sentient being saying things like current takes the path of least 
resistance like it worked it out. Well, the poorly conducting layer of 
corrosion on the surface of wire isn't the path of least resistance is 
it? That layer is some of the infinite number of parallel paths and will 
get a portion of the current flow in inverse proportion to its 
conductivity compared to the uncorroded conductor.

A question:

Are we considering corrosion so advanced as to reduce the cross 
sectional area of the wire, effectively reducing the surface area of 
good copper available for skin effect conduction so increasing the wires 
impedance?

My apologies to anyone offended by my getting too close to calculus.

Patrick        NJ5G


On 12/28/2016 12:28 AM, Guy Olinger wrote:
> Current betting money in my neck of the woods is on some actual
> deterioration of the surface of the copper caused by compounds in the
> degrading insulation. Skin effect forces some degree of current into
> the degraded copper which has a higher resistance than the non
> deteriorated good stuff in the middle of the wire.
>
>