13 - Telephone Cables

Abstract

Telephone cables need more corrosion protection measures than pipelines because of their particular construction and operating conditions. All telephone cables have either a completely solid metal sheathing around the core or in the case of completely plastic cables, a metal band as an electric shield. Passive corrosion protection of telephone cables can be achieved by coating the metallic cable sheathing. In the past, lead was mainly used for cable sheathing. Today steel, copper, and aluminum are being increasingly used as the sheathing material or shield. For direct burial, the lead sheathing is protected against corrosion by alternating layers of impregnated paper and viscous bitumen. Cables of small diameter are mechanically protected with closely wound round wires, and those of larger diameter with flat tape reinforcement. A layer of impregnated jute is applied over the reinforcement that gives some corrosion protection, but does not insulate the cable sheathing from the soil. In contrast, PE sheathing, free of junctions and pores, 1.6 mm to 4.0 mm thick, is also used. Cathodic protection is, thus, mainly applied to jute-covered, lead-sheathed cables and plastic-sheathed cables that have external reinforcement. Cables with other metallic sheathing can be included in cathodic protection, but special arrangements must be made.