Arcing of electrical contacts in telephone switching circuits: Part I — Theory of the initiation of the short arc

This is a presentation of a theory for the mechanism of the initiation of the short arc commonly observed on the closure and opening of electrical contacts. The theory is based on the experimental evidence that an established arc is generally preceded by a period of local high frequency discharges at the contacts. During this period the circuit current builds up. If and when this current reaches the arc initiation current of the contact a steady arc is established. It is shown that this initiation period of the arc is directly determinable from the circuit conditions and the contact condition. This mechanism furnishes rather simple explanations to some complex phenomena commonly observed before the establishment of the arc. The mechanism of the initiation of an individual discharge, however, still remains uncertain.