Contact Phenomena in Telephone Switching Circuits

The phenomena occurring at the closing and opening of contacts carrying weak currents have been investigated by means which include a study of the high-frequency transient voltages and currents. These influence the erosion in a complex manner which varies with contact materials, surface conditions, and surrounding atmosphere. Three principal classes of effect have been distinguished. These are: (1) Disruptive spark-overs initiating a series of metallic arcs lasting less than a microsecond each. (2) A nitrogen-gas glow discharge at about 300 volts, preceded by a brief group of disruptive spark-overs. (3) High field breakdowns due to cold point discharges which cause transient metallic closures of approaching contacts and similar transient reclosures of separating contacts.