Incidents involving contact between heavy equipment and overhead power-lines are more common than you might imagine. Some of the more typical occurrences include workers lifting loads with cranes, operating trucks with raised beds, and placing drilling equipment into position. In each of these instances, the danger exists because workers failed to realize just how close they were to power lines.
Machinery that makes contact with an overhead power line conductor becomes energized with electricity ranging from several thousand to more than 10,000 volts. When this happens, there are three ways that injury can occur:
- Workers in direct contact with both the machine and ground become a pathway for electrical current.
- Equipment operators, who are unaware of the line contact, or of their imminent danger, dismount the equipment, which causes them to bridge the high voltage between the equipment and ground.
- Nearby workers who try to help co-workers involved in the incident make contact with energized equipment or victims.
Because accidents involving power lines and heavy equipment are such a problem, OSHA established the following guidelines:
- All equipment covered by Subpart O—Motor Vehicles, Mechanized Equipment, and Marine Operations, must comply with 1926.550(a)(15) when working or being moved in the vicinity of power lines or energized transmitters.
- Any overhead line must be considered energized unless and until the person owning the line or electric utility authorities indicate that it is not and has it visibly grounded. There are three OSHA approved methods to protect equipment operators from coming into contact with live overhead lines:
- De-energize lines and visibly ground them before work begins. The owner of the property or the utility company is responsible for performing this step.
- Construct insulating barriers that are separate from the equipment to prevent physical contact with the lines.
- Operate equipment only if the required clearance between the lines and the equipment exists. If the line is rated 50 kV or below, there must be a 10 foot clearance. If the line is rated over 50 kV, there must be a minimum of 10 feet plus 0.4 inch for each 1 kV over 50 kV. Keep in mind that the required amount of clearance must be between the line and all parts of the equipment.
- Transporting crane-type equipment with no load and boom lowered requires a minimum of 4 feet of clearance for voltages less than 50 kV, and 10 feet of clearance for voltages between 50 kV and 345 kV. Voltages over 345kV, up to and including 750 kV, require a 16 foot clearance.
- A person must be designated as a spotter to ensure line clearance of the equipment. The spotter is also required to give a timely warning for all operations where it is difficult for the operators to see if they are maintaining the desired clearance.
