The `melting´ voltage in electrical contacts

In some electrical contacts, equilibrium between heat generation and dissipation is never attained beyond a threshold temperature. At this temperature, the rate of thermal dissipation by conduction through the solid decays too rapidly with increasing temperature, leading to heat entrapment. The heat accumulation causes rapid contact melting at a potential drop across the contact appreciably smaller than the conventional melting voltage. The author reports on an investigation of the melting voltage in Fe/Fe, Ni/Ni, and W/W electrical contacts where the thermal runaway effect mentioned above is expected. In agreement with earlier work, the melting voltage for Fe/Fe couples is found to be smaller than the value predicted by the conventional voltage-temperature relation. Similarly, Ni/Ni contacts melt at a low potential drop. However, melting is not observed by W/W contacts at contact temperatures as elevated as 890°C. This is contrary to the prediction of the theory that accounts successfully for the melting of Fe and Ni contacts. The reasons for this discrepancy with theory are discussed