Investigation of ampacity derating factors for shuttle cars using fiber optics technology

The overheating of electric cables on mine shuttle cars has long been recognized as a cause of premature insulation failure leading to shock and electrocution. The use of cable reels on shuttle cars can cause excessive heat build up which, in turn, causes the cable insulation to soften and become easily damaged. This heat-softened insulation reduces the life of the cable. Repeated cycling of a cable in this manner can cause premature aging of the insulation; it becomes brittle, cracks and allows electrical leakage paths to form. These leakage paths provide the opportunity for shock and electrocution to occur if miners come in contact with the damaged section of cable. It is imperative that cable operating temperatures be maintained at safe thermal limits. This paper discusses a research project conducted by tire National Institute for Occupational Safety and Health, Pittsburgh Research Center, to determine dynamically the conductor temperature of reeled shuttle car cables using fiber optics technology. The research portrays typical shuttle car loading cycles (both current and time cycles). Root-mean-square current loading is calculated based on the results. The thrust of this effort is to provide a scientific basis for ampacity derating factors specifically for mine machinery using reeled cables. This information will reduce the probability of electrical hazards from reeled cables