Investigation and status report on concentric neutral corrosion of URD extruded cable. Final report

Abstract

The use of cables with extruded insulation and concentric neutral wires has been widely accepted for underground distribution in recent years and substantial continued use of this cable is anticipated. Recent reports of incidences of corrosion of the neutral strands have produced concern about problems which may result. The integrity of the neutral wires is important because it provides a low impedance both for load and short circuit currents and maintains acceptable voltage levels to equipment and personnel during short circuit conditions. A compilation of the information obtained from a literature search and a field investigation is presented. Results obtained in corrosion surveys of underground residential distribution (URD) cables are also included. The study concentrated on ascertaining present opinions about the cause or causes of concentric neutral corrosion and on determining present industry practice in corrosion mitigation. This investigation found no general agreement about the cause of concentric neutral corrosion and indeed there was even disagreement about the extent and seriousness of the problem. It is concluded that the neutral corrosion results from either stray dc currents or natural galvanic action and that ac is not an important factor. Present mitigation practice focuses mostly on jacketing and cathodic protection. Theremore » is a need for additional work in determining the effectiveness of these practices and in prescribing procedures for their use.« less