Glowing contact areas in loose copper wire connections

Abstract

Laboratory experiments have shown that, when a current-carrying, loose copper wire connection is exposed to mechanical vibrations, a layer of Cu/sub 2/O grows to form a bridge between the contact members, bonding them to one another. Due to the strongly negative temperature coefficient of Cu/sub 2/O 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 Cu/sub 2/O to a depth of a few tenths of a mm. As the corrosion proceeds the power dissipation increases to values which can 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 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 of less than 1 ampere.<>