A new mechanism for the operation of a cathode spot in a vacuum arc, based on ecton processes, is proposed. An ecton is formed by the explosion of the tip of a jet of molten metal as it interacts with plasma. It is suggested that the time over which an ecton functions is limited by the thermal conductivity of the liquid metal. Theoretical expressions are derived for the specific amount of mass removed, for the ion erosion, for the current, and the for the diameter of the craters for a copper cathode. The results agree satisfactorily with experimental data. © 1994 American Institute of Physics.