Corrosion of Metals---II. Lead and Lead-Alloy Cable Sheathing

HE intricate cable network of the telephone system offers numerous opportunities for the occurrence of corrosion. The property d a m a g e resulting f r o m perforation of the sheathing by corrosion a n d the attending costly interruption of service have served to make the prevention of cable failure a matter of primary concern. The relatively low incidence of actual corrosion failures can be attributed largely to the vigilance of the electrolysis engineers and the plant forces. Cable sheathing is one of the largest single uses of metallic lead. In 1929 it exceeded even that employed in the manufacture of storage batteries and constituted about 27 per cent of the entire consumption in this country. In the past fifteen years over two million tons of lead have gone into the communications and power cable plants. In the Bell System alone there are about 180,000 miles of lead alloy covered cables, about forty per cent of which are underground. About 95 per cent of the total mileage of telephone wires is in cable, the proportion of open wire construction decreasing each year. The earliest telephone cables were of the type employed in telegraph practice, the individual wires being insulated with rubber or gutta 603 i 604 BELL SYSTEM TECHNICAL JOURNAL percha and the core covered with a rubber or textile sheathing. The first lead-covered telephone cables were made by David Brooks, Jr., and were installed in the year 1880. These consisted of cottoncovered wires drawn into a lead pipe--a moisture-proofing compound of rosin and paraffin being forced afterward into the pipe and allowed to solidify by cooling.