Arcing of Electrical Contacts in Telephone Switching Circuits: Part V -Mechanisms of the Short Arc and Erosion of Contacts

The problem of contact erosion due to arcing has been the subject of a large number of investigations. The literature includes a considerable accumulation of data on the erosion characteristics of many contact materials. Due, however, to the vast variations in testing conditions adopted, there are considerable disagreements and discrepancies among results from different investigations. Inconsistencies even within one investigation are not uncommon. 1081 1082 TIIE B E L L SYSTEM TECHNICAL JOURNAL, S E P T E M B E R 1955 In general, the erosion behavior of contacts depends, to varying degrees, on the following main parameters: the physical properties of the contact material, surface conditions, contact geometry and separation, arc duration, arc current ant. the surrounding atmosphere. In our study, most of these parameters were considered separately, whenever possible, with the primary objective of clarifying the mechanisms involved. Most experiments reported here are, in effect, of the probing type designed to test specific postulates and assumptions. The first section of this paper is a summary of the experimental work done and the results obtained. In the second section, the data are analyzed and a tentative working model is proposed for the short arc and its erosion effects. Because of the rather extreme complexity of the phenomena and the lack of basic data on the conduction properties of metal vapors, this model is at best a simplified one and is probably incomplete in some respects.