I have owned, built, and used a lot of cables. The only cables I have that have oxidized to any noticeable extent were old Monster stranded speaker cable covered in their clear, rubbery-feeling PVC casing. The interface between the wire and the casing turned green and, when cut, the wire was clearly oxidized throughout the entire thickness. I have other copper cable/wire over 20 years old that show no visual signs of corrosion, even at the ends which have not been connected to anything for years.
My experience is that good-quality copper, in most dielectrics should not noticeably corrode, except maybe at the connections if they are exposed to harsh environments - such as connecting wires in my pool heater. This could be caused by
galvanic corrosion, which requires two dissimilar metals to be in contact and also requires a wet environment (a conductive liquid). Another type of reaction can occur when sulphur is present in the environment as copper sulfide
can turn copper black. I suspect currently manufactured, purpose-built audio cables using at least OFC should not have corrosion problems. For the cables I have constructed from cotton covered copper, I wrap the assembly with a thicker-than-typical (and therefore more abrasion-resistant) teflon tape.
I did some internet research on the cause of the greenish corrosion I observed on my Monster cables and found it is related to compounds in the PVC covering, mostly prevalent from about 1965 to 1971. However, since Monster was not founded until 1979, I suspect the reported time-frame is incorrect. The text below is what I found that mostly summarizes the commonly reported cause of the green color and subsequent corrosion;
"Flexible PVC contains plasticizers which can be any compatible material that allows the polymer chains to move more easily and impart flexibility. One such material and very commonly used is DOP, di-octyl phthalate also known as DEHP, Di ethylhexyl phthalate.
Initially when flexible PVC is heated two processes tend to occur (introduction of UV or more powerful radiation complicates matters):
1 The plasticiser becomes mobile and wants to diffuse out of the PVC,
2 HCl is released.
The dominant of these two depends on temperature, the higher the temperature, the more favourable to #2.
If the flexible PVC is a cable insulation in contact with Cu and heated e.g. highly loaded mains cable, the HCl will react with the copper to form copper chloride which can absorb water vapour if conditions favour and/or complex with the plasticiser (DOP) to form a green "gloop". (the chemistry behind the green colour is complicated )
It is the action of HCl which is important as it not only causes corrosion in the copper or other metal components, it also catalyses further degradation of the PVC and more HCl release so that the whole process can "run away with itself". If the HCl can escape, the process is less active; in a cable or unventilated enclosure the problem can be severe."
