Thermal characteristics of energized coal mine trailing cables

The US Bureau of Mines conducted research to determine the relationship between current load and temperature rises in coal mine trailing cables. Six low-voltage unshielded portable power cables were continuously and intermittently loaded with direct current of various magnitudes. Relationships between average temperature at the conductor/insulation interface and current load were established. The steady-state and intermittent currents that produce a 90°C average conductor/insulation temperature were then determined by mathematical modeling. Comparisons to Insulated Cable Engineers Association steady-state ratings revealed that 10-25% more current is required to reach rated insulation temperature. Examination of the maximum intermittent temperatures attained showed that auto-ignition of coal dust and burns to personnel handling the cable would not be concerns if the temperature at the conductor/insulation interface averaged 90°C