Arcing at Electrical Contacts on Closure. Part V. The Cathode Mechanism of Extremely Short Arcs

Abstract

The available experimental data on the short arcs which occur on closure of electrical contacts with potential differences less than the minimum sparking potential are shown to be consistent with the hypothesis that the arcs are initiated and sustained by field emission electrons. Positive ions then carry less than 7 percent of the current at the cathode. The primary function of the ions is to supply sufficient positive space charge to maintain the high cathode field, but the action of the discrete ions near the cathode in creating a temporary pass in the potential barrier may result in the attainment of sufficient electron emission to sustain the arc at values of the cathode field somewhat lower than that required by the Fowler‐Nordheim equation for the same current density. It is shown that the supply of volatile impurities on the electrode surfaces is critical in determining the breakdown field and the minimum arc current.