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 degrees 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 degrees C.
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