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Look Out (Above) for Overhead Electrical Power Lines

- May 30, 2014 by Glen O'Rourke, ALCM (View all posts by Glen)

When evaluating outdoor work, don’t forget to consider that a hazard could be lurking from above: electrocution from overhead electrical power transmission lines.  Due to the high voltages involved, overhead power lines are to be considered uninsulated.  If equipment that is capable of conducting electricity comes in contact with or is even in close proximity to overhead power lines, electricity could flow from the lines through the equipment, and then to people operating the equipment or in the immediate area and thus result in electrocution.

Examples of equipment particularly susceptible to this potential hazard are:

  • Cranes
  • Aerial lift platforms (scissor lifts, boom lifts, bucket lifts, etc.)
  • Excavators and backhoes
  • Aluminum ladders
  • Aluminum extension poles (such as those used for window washing)
  • Forklifts
  • Trucks with raised dump beds

If any work is to be performed near overhead power lines using such equipment, proper safe work practices need to be established and followed.  Such safe work practices could include:

  • Contacting the utility and having them shut off and reroute the power to those particular overhead lines.
  • Contacting the utility and having them install temporary protective insulation over those particular overhead lines.
  • Constantly maintaining minimum clearance from the equipment to the power lines.

Minimum clearances have been established because of the phenomenon of arcing.  Proximity to high voltages poses a hazard since electricity can flow through ionized air molecules and thus “jump” a gap between a conductor at high voltage to another at lower voltage.  The minimum clearance distance from the power lines to the equipment depends on the voltage of the lines.  Distances that need to be maintained are:

  • 10 feet for lines up to 50,000 volts
  • 15 feet for lines from 50,000 to 200,000 volts
  • 20 feet for lines from 200,000 to 350,000 volts
  • 25 feet for lines from 350,000 to 500,000 volts
  • 35 feet for lines from 500,000 to 750,000 volts
  • 45 feet for lines over 750,000 volts

Following safe work practices can help prevent electrocutions when outdoor work is being performed near overhead electrical power transmission lines.  Next time you are working outside, make sure everyone remembers to look out (above) for overhead power lines.

References:

“Electrical Safety-Safety and Health for Electrical Trades Student Manual.”  CDC.gov.  Department of Health and Human Services,  Centers for Disease Control and Prevention and National Institute for Occupational Safety and Health Publication, April 2009. Web. 31 March 2014.  http://www.cdc.gov/niosh/docs/2009-113/pdfs/2009-113.pdf

“High Voltage Overhead Lines.” Dir.ca.gov. California Department of Industrial Relations, Division of Occupational Safety and Health, September 2011.  Web. 31 March 2014.  http://www.dir.ca.gov/dosh/dosh_publications/tb_highvoltage.pdf

 
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