Department of Labor
Mine Safety and Health Administration
On October 29, 2004, a mechanic, who was changing a tire on a roof bolting machine received an electrical shock. The electrical shock was a result of a phase-to-ground fault on the high voltage system, which provided power to the section power center. Although the circuit breaker which provided power to the bolter had been opened, the cable coupler for the roof bolter trailing cable remained connected to the power center while the repairs to the roof bolter were taking place. The metallic frame of the roof bolter became momentarily energized during the presence of these faults through the grounding system until the high voltage protective device opened. The tires of the roof bolter effectively insulated the bolter frame from the mine floor. When the mechanic came into contact with the bolter frame when tightening the wheel lugs while he was in contact with the mine floor, he provided an additional path for the fault current to flow.
How could this incident have been prevented? When performing mechanical work MSHA's Policy for §75.1725 (c) requires that the trailing cable shall be disconnected from the source of power before repairs are made on portable or mobile equipment. Unplugging the roof bolter trailing cable at the power source before performing the mechanical work of changing the roof bolter tire could have prevented this incident.
- Remove the trailing cable from the power source before making repairs on equipment
- Lock-out and Tag equipment being repaired
- Wear protective gloves when performing work which could result in injury to hands
This information was provided by concerned miners in an effort to eliminate accidents. Accident or "close call" information within District 8 may be shared by contacting
the MSHA office at (812) 882-7617.