Electrical safety — Mine

Scope

Regulatory citations

• 30 CFR Part 56 — Electricity

Key definitions

• Distribution box: A portable apparatus with an enclosure through which an electric circuit is carried to one or more cables from a single incoming feed line, each cable circuit being connected through individual overcurrent protective devices.

Summary of requirements

• Make sure fuse and circuit breakers match the equipment and current loads.
• Provide and properly install switches and controls of approved design and construction.
• Provide electrical conductors of sufficient size and capacity to ensure that elevated temperatures from normal operation will not damage the insulation.
• Protect electrical conductors from mechanical damage.
• Provide distribution boxes for each branch circuit with a disconnect device. Label each disconnect device with the circuit controlled.
• Label all principal power switches to show which units they control unless identification can readily be made by location.
• Protect power conductors from:
  • Mobile equipment running over them
  • Loads dragged over them unless they are bridged.
  • Do not make "hot" connections to trailing or power cables.
• Permanent splices and repairs must be:
  • Mechanically strong
  • As near the original electrical conductivity as possible
  • Insulated to at least the same degree as the original
  • Sealed against moisture
  • Provided with damage protection as close to the original as possible.
• Use proper fittings, insulation and bushings where appropriate when passing cables or wires in and out of compartments, motors, frames and other housings,
• Keep inspection and cover plates in place except during testing or repairs.
• Ground all metal casings or housings, buildings, or fences for electrical equipment for transformers and switchgear, and mobile equipment. Battery-powered equipment doesn’t need to be grounded.
• Follow one of these options for transformers:
  • Total enclosure;
  • Placement at least eight above the ground; or
  • Surrounded by a substantial fence at least six feet high and at least three feet from any energized parts, casings or wiring if placed in a building.
• Post appropriate danger signs at all electrical installations.
• Guard or protected by location all electrical connections and resistor grids if insulation is difficult or impractical.
• Test for continuity and resistance immediately after installation, repair or modification of electrical system. Annual tests are required thereafter. Keep a record of resistance measurements for the most recent test and make available to MSHA on request.
• Correct potentially dangerous conditions before equipment or wiring is used.
• Deenergize equipment or circuits (unless hot-line tools and techniques are used) before working on them, called "Lockout/Tagout" in the general industry regulations. The power must be turned off and positively locked out or tagged out. Post warning notices at the power switch. Equipment requires the signature of the individuals involved. The locks, signs and other preventative devices may only be removed by the person(s) who installed them or authorized personnel.
• Provide individual overload or short circuit protection when using trailing cables.
• Attach trailing cables in a suitable manner to protect the cable and prevent strain on the electrical connection.
• Store surplus trailing cable for shovels, cranes, and similar equipment in cable boats, on reels, or some equivalent carrier.
• Use insulated slings or sleds when handling energized power cables over 150 volts, phase-to-ground, such as those used on mobile equipment.
• Guard portable extension lights or similar lights that by their location present a shock or burn hazard must be guarded.
• Weatherproof any lamp sockets exposed to wet conditions or weather.
• Provide adequate access clearance at stationary electrical equipment or switchgear.
• Keep dry wooden platforms, insulating mats, or other electrically nonconductive material in place at all switchboards and power-control switches where shock hazards exist.
• Allow only authorized persons to enter major electrical installations.
• Keep transformer enclosures locked.
• Deenergize and isolate abandoned electrical circuits to prevent re-energization.
• Deenergize high-voltage powerlines (or use other protective measures) whenever equipment moves near them (not including trolley lines) with a clearance of less than 10 feet.
• See the section on explosives for the electrical safety considerations, especially 30 CFR 56.6402 and 30 CFR 56.6404.