Heat transfer characteristics of mining cables

The author discusses the recommendations of the Insulated Cable Engineers Association (ICEA) for ampacity on a 4/0 AWG type-SHD-GC 8000 V cable and compares this to the industry standard Neher-McGrath calculation for ampacity. For comparison, a 4/0 SHD was tested thermally in the laboratory and the results compared to the calculation. It is found that cables properly sized for voltage drop and load should not overheat in any of the thermal environments discussed. To be sure of the proper cable size, the worst case situation for the cable must be calculated in advance of selecting the conductor size. Problems will arise in situations in which the cable is reeled or coiled, and allowances were not made for this in the original ampacity calculation. It is also found that ICEA ampacities are very precise for the larger SHD-GC cables and 10-15% conservative for the smaller cables. Cable buried in soil will operate 5% higher in conductor temperature than the aerial cable on the lower end of the tests and at least 10% hotter as the aerial cable approaches 90 degrees C and should be derated accordingly. Cable on top of soil will run 1-6% higher in conductor temperature than the aerial cable, depending upon current levels.<>