How can we determine the conductivity & purity of a copper bus bar after using it for several years with dedicated electric load?

Copper bus bar in switchgear has still the conductivity properties even on continuous years of usage (on rated ampacity of bus bars) and always be. Regarding the purity, copper remains on its state for it resists corrosion and has high thermal conductivity. Maybe you just see insulation breakdown that's why you wonder copper's reliability as an electric conductor. A serious fault experienced by a bus bar conductor is visible when thouroughly inspected such as the insulation, color of the conductor, arcing,etc...