Contact bridge erosion and its prevention

AS ELECTRIC CONTACTS separate, a molten metallic bridge forms between them and then breaks. A transfer of contact material, called bridge erosion, accompanies the rupture of the bridge. If the inductance in a d-c circuit is reduced sufficiently and if the battery voltage is below the minimum for arcing, the phenomena of the molten bridge can be isolated for study. Careful examination of contacts operated under conditions in which bridge erosion predominates shows that, despite a gross transfer of material from anode to cathode, the explosion of a molten bridge leaves a small crater in each contact. The diameters of such craters are believed to be those of the molten bridge just before rupture and they vary with current and with resistivity of the contact material and in the expected manner.