Glowing contact areas in loose copper wire connections

Laboratory experiments are reported that show that when a current-carrying loose copper wire connection is exposed to mechanical vibrations, a layer of Cu₂O grows to form a bridge between the contact members, bonding them to one another. Due to the strongly negative temperature coefficient of Cu₂O at high temperatures, the current is concentrated in a thin, glowing filament at or near the surface of the oxide bridge. The maximum temperature of this filament was found to be 1200-1300°C. Under the action of this hot filament, a rapid oxidation of the copper continues until most of the circumference of the copper wires is converted to Cu₂O to a depth of a few tenths of a millimeter. As the corrosion proceeds, the power dissipation increases to values that can cause fire hazards. The phenomenon described explains how a temperature high enough to initiate a fire can arise, even when the current through the connection is limited by the load impedance to values less than 1 A