Experimental investigation of the effect of semiconducting cable jackets on adjacent steel structures

Currently, RUS, the federal agency that regulates electric cooperative utilities, requires insulating jackets on medium voltage underground power cables. This requirement is primarily based on a series of papers written in the 1970s, which hypothesized that cables with semiconducting jackets accelerate the corrosion of adjacent steel structures. To evaluate this hypothesis, a test program was designed to simulate field conditions as closely as possible. The program contained medium voltage cables with semiconducting jackets, cables with insulating jackets and cables with no jackets buried adjacent to galvanized ground rods. Galvanic currents and voltages were measured over a period of a year. The cables and ground rods were then removed from the ground and examined. The results demonstrate that cables with semiconducting jackets do not enhance the corrosion of adjacent steel structures. In fact, semiconducting jackets significantly reduced the corrosion of adjacent steel ground rods when compared to cables with bare neutrals. While the least amount of corrosion occurred on steel ground rods adjacent to cables with insulating jackets, ground rods adjacent to cables with a semiconducting jacket had corrosion characteristics that were very similar to rods adjacent to cables with an insulating jacket.