John I English

US Patent:

40372669, Jul 19, 1977

Filed:

Dec 29, 1975

Appl. No.:

5/645073

Inventors:

John Hershel English - North Plainfield NJ
James Edward Griffiths - Murray Hill NJ
Paul Zuk - Allentown PA

Assignee:

Bell Telephone Laboratories, Incorporated - Murray Hill NJ

International Classification:

H02H 322

US Classification:

361120

Abstract:

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.