Electrical Requirements at Surface Mines

Telephone and low-potential signal wire must be protected, by isolation or suitable insulation, or both, from contacting energized power conductors or any other power source. Power lines must be well separated or insulated from water lines, telephone lines, and air lines.

Power wires and cables must be insulated adequately where they pass into or out of electrical compartments. Cables must enter metal frames of motors, splice boxes, and electrical compartments only through proper fittings. When insulated wires, other than cables, pass through metal frames, the holes must be substantially bushed with insulated bushings.

The electrical potential on bare signal wires accessible to contact by persons must not exceed 48 volts. Where metallic tools or equipment can come in contact with trolley wires or bare power lines, the lines must be guarded or de-energized.

Trolley wires and bare power conductors must be guarded at mantrip loading and unloading points, and at shaft stations. Where such trolley wires and bare power conductors are less than seven feet above the rail, they must be guarded at all points where persons work or pass regularly beneath.

Electrically powered equipment must be de-energized before mechanical work is done on such equipment. Power switches must be locked out or other measures taken to prevent the equipment from being energized without the knowledge of the individuals working on it. The individuals who are to do the work must sign and post suitable warning notices at the power switch. Only authorized personnel or the person who installed the locks or preventive devices may remove them.

Trailing cables must be attached to machines in a suitable manner to protect the cable from damage and to prevent strain on the electrical connections. Surplus trailing cables to shovels, cranes, and similar equipment must be handled in one of the following ways:

• Stored in cable boats
• Stored on reels mounted on the equipment
• Otherwise protected from mechanical damage

The guy wires of poles that support high-voltage transmission lines must meet the requirements for grounding or insulator protection of the National Electrical Safety Code, Part 2, "Safety Rules for the Installation and Maintenance of Electric Supply and Communication Lines."

Portable extension lights, and other lights that by their location present a shock or burn hazard, must be guarded.

Power lines (including trolley wires) and telephone circuits must be protected against short circuits and lightning. Each ungrounded conductor or telephone wire that leads underground and is directly exposed to lightning must be equipped with suitable lightning arresters of an approved type within 100 feet of the point where the circuit enters the mine. Lightning arresters must be connected to a low-resistance grounding medium on the surface, and must be separated from neutral grounds by a distance of not less than 25 feet.

Power circuits must be de-energized before work is done on such circuits unless hot-line tools are used. The individuals who are to do the work must post suitable warning signs. Suitable danger signs must be posted at all major electrical installations.

To learn more about MSHA Part 48 training requirements visit our MSHA Part 48 Subpart B Surface Mining Online Training web page.