Lightning Surges in Paired Telephone Cable Facilities

Abstract

The problem of protecting apparatus against lightning surges from connected transmission facilities has become more complex with the use of solid state devices in apparatus design. Consideration of the protection requirements for such apparatus has indicated that existing information concerning the incidence and characteristics of lightning surges is insufficient to develop optimum protection measures. A recently completed field investigation provides additional information in this specific area. The results of this field investigation and supplemental laboratory surge tests indicate that, in well-shielded underground cable pairs, electrical surges do not exceed approximately 90 volts peak, and that transistorized apparatus capable of withstanding such surge amplitudes needs no further protection. In aerial and buried cable, however, transistorized apparatus requires protection up to the full sparkover potential of 3-mil protector gaps, i.e., to about 600 volts peak. A firm basis for testing and evaluating transistorized apparatus from the lightning surge voltage standpoint is presented.