Hi Argon,
Copper does oxidize over time when it's exposed to air--you know those rooves made of copper that turn greenish, as well as copper pennies. Where it's exposed at the connection point, electrical conductivity may be affected. You can use a bit of sandpaper to remove the oxidation if you are using bare-wire connections and return the lustre to the copper.
If memory serves, it seems that other forum members have warned users away from Home Depot's bulk generic speaker wire because it seemed to oxidize even under the plastic insulation, which is odd. Even so, that won't affect conductivity through the copper.
Does anyone else recall those posts?
Regards,
Alan
