Bell Telephone Laboratories

John Hershel English

Paul Zuk

James Edward Griffiths

Electrical equipment, such as telephone station apparatus, exposed to occasional, destructively high, voltage surges (e.g., lightning strikes) is protected by a device, placed in parallel with the equipment, including two electrodes defining a fixed narrow spark gap which breaks down (arcs over) to short the voltage surge to ground. The predominant failure mode of such devices is shorting across the narrow gap, due to electrode damage produced during the protective arcing mode. In the disclosed devices, the electrodes are contoured to define a narrow region, determining the protective breakdown voltage, and a wider region, sustaining the major part of the electrode damage. Shortly after the initiation of the protective discharge in the narrow gap region, the discharge moves into the wider gap region. Since the major portion of electrode damage is sustained by the wider gap region of the electrodes, the incidence of shorting failure is suppressed. An exemplary electrode profile includes a flat central region and a surrounding tapered region.

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North Plainfield, NJ, United States of America

John Hershel English