Safety analysis of trailing cables used on 2400-V continuous mining machines

An analysis was performed to determine whether an increased shock hazard occurs with 2400-V continuous-miner trailing cables, as compared with those used with existing low-and medium-voltage systems. (It should be noted that the Code of Federal Regulations defines low, medium, and high voltages for mine power systems as 0-660, 661-1000, and > 1000 V, respectively.) The study assumed that the Mine Safety and Health Administration's Proposed Rule for High-Voltage Continuous Mining Machines was implemented with the exception of the special cable-handling requirements. Two major differences between the high-voltage proposed rule and existing low-and medium-voltage regulations that are relevant to this study deal with ground-fault protection and include the following: 1) The maximum ground-fault current of the 2400-V system must be limited to 0.5 A, while low-and medium-voltage systems typically use a 15-A limit; and 2) the maximum ground-fault pickup of the 2400-V system must be set at 0.125 A with a maximum time delay of 0.05 s, whereas low-and medium-voltage systems require an instantaneous pickup set at, or below, 40% of the maximum ground-fault current (6 A for 15-A systems). Results of the study show that 2400-V trailing cables, in conjunction with the stricter ground-fault protection requirements and enhanced cable construction, provide a higher level of safety compared with trailing cables used on low-and medium-voltage continuous miners.