Polyethylene, a plastic used as an insulation over the copper conductor in telephone wires, can oxidize in the presence of atmospheric oxygen (and ozone), especially in hot geographical locations like Arizona. Environmental conditions, such as air pollution, and residential cable-filling compound remaining on the wire insulation can accelerate oxidation and lead to a shorter life for the wire insulation.
As a result of oxidation of insulation, copper wire loses its ability to carry data and voice, resulting in deteriorated telephone service. The rate of oxidation is higher in high temperature and highly polluted environments. Yuma, Arizona's average annual temperature is 30 degrees C. This figure can go as high as 50 degrees C in the summer. The town's air is highly polluted with suspended particles from insecticides, pesticides, airplane activity, and upper-atmosphere ozone layer thinning.
AT&T Bell Laboratories studied a Yuma telephone cable containing insulated wire that began service in September 1978. Ten feet of the insulated wires, including a portion exposed to the atmosphere, was removed in 1986 and studied. Normally, part of the exposed portion of the cable core inside the pedestal is bent as illustrated below.
See Sheath and Three Sections of Unsheathed Wire graph
None of the insulation studied showed any signs of cracking. Experimenters divided the cable into three sections: Section I was close to the cable; Section II was the bent area; and Section III was the free end of the exposed wire. They also tested samples of the insulated wire that had remained sheathed.
Particules, appearing as dirt, attached themselves to the cable-filling compound covering the insulation in all three sections of the wire. Wire insulation with particules attached is designated "as is;" after removing the particules with a paper towel the wire is designated "cleaned."
The oxidation induction time (OIT) values of under
sheathed wire insulation was compared to those of those of the exposed wires
to show the effect of the environment on the stability of wire insulation. The
"as is" and "cleaned" samples were adjacent to each other to eliminate