The `melting´ voltage in electrical contacts

An investigation of the melting voltage in Fe/Fe, Ni/Ni, and W/W electrical contacts is presented. The Ni/Ni system is investigated to establish potential operating limits of nickel-plated aluminum conductors. The work on Fe/Fe contacts is undertaken in part to confirm the validity of the experimental approach by confirming observations of contact melting in an earlier investigation. The W/W system is investigated to identify any effect of the growth of electrically conductive oxide around the contact on the melting voltage, since tungsten oxide is known to grow relatively rapidly in oxygen at elevated temperatures. 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 in 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