Ampacity ratings of bundled cables for heavy current applications

Large electric glass melters and similar heavy current applications use bundled cables of high ampacity conductors. Typically, a bundle of insulated, flexible, multistranded conductors are used in parallel to meet the high ampacity requirement for each phase cable. For sizing purposes it has been the normal practice to determine the number and size of the bundled parallel conductors in each phase from the total phase current requirement, and the ampacity rating of each candidate conductor, assuming equal current distribution in the bundle. In such heavy current applications additional design precautions must be taken to insure that the ampacity of each member conductor in the bundled cable is not exceeded due to the “skin effect” phenomenon. This phenomenon manifests itself as an electromagnetic field inside the bundle which tends to drive most of the current toward the outer-most conductors. This results in a nonuniform distribution of currents in the conductors. In a previous paper, a model was developed to predict the current distribution in such high current bundled cables. This paper focuses on the utilization of that model to develop simple tables to aid engineers in the rating and selection of high ampacity bundled cables for heavy current applications. This information is intended to provide cable sizing data in a form similar to that found in the NEC and for a wide range of applications