Influence of Potassium on the Arcing Voltage of Reed Contacts

Sealed reed contacts used in switching matrices are subjected to cable discharges which generate short arcs on make. This type of arc burns at a characteristic arc voltage. When the contact material is changed from pure gold to cobalt hardened gold, a large decrease, approximately 4 to 5 V, in the mean arcing voltage is observed. This decrease in arc voltage is associated with an increase in the probability of generating an arc. The arc characteristics are attributed to the presence of potassium in the gold electroplate. Desorption of potassium ions has been demonstrated in the hard gold remreed coatings at a rate of 10⁹K+ sec-1 when the remreed was at 425°C. This last experimental observation helps to resolve the discrepancy between the hard gold mean arc voltage and the Kisliuk model.