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

To: towertalk@contesting.com
Subject: Re: [TowerTalk] UV and WX deterioration of THHN insulation, and effects
From: Patrick Greenlee <patrick_g@windstream.net>
Date: Wed, 28 Dec 2016 07:51:45 -0600
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
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.



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