GLOWING CONTACT AREAS IN LOOSE COPPER WIRE CONNECTIONS

Laboratory experiments have shown 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-degrees-C. Under the action of this hot filament a rapid oxidation of the copper continues until in the end most of the circumference of the copper wires has been converted to Cu2O to a depth of a few tenths of a millimeter. As the corrosion proceeds, the power dissipation increases to values, which can without doubt, cause fire hazards if a similar situation occurs in electrical apparatus or installations. According to statistics, loose connections or broken wires are known to be the cause of many fires. The phenomenon described in this paper 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.