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-voltage, medium-voltage, and high-voltage for mine power systems as 0-660 V, 661-1000 V, and greater than 1000 V, respectively.) The study assumed that Mine Safety and Health Administration's Proposed Rule for High-Voltage Continuous Mining Machines was implemented with the exception of the special cablehandling 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: 1) The maximum ground-fault current of the 2400-V system must be limited to 0.5 A, while the low and medium-voltage systems typically use a limit of 15 A, 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 the 2400-V trailing cable, in conjunction with the strict ground-fault protection requirements and enhanced cable construction, provide a higher level of safety compared with the trailing cables used on low and medium-voltage continuous miners.