Module 4:Overhead and Underground

Power Lines

Overview of Module 4

• Background on power lines• Hazards of overhead and underground

power lines• Injury prevention techniques• Summary

Background• Power lines transmit electricity• Electrical current exposes

workers to serious hazards– Most common hazard is

electrocution– Most workers are unaware of

potential electrical hazards • Power lines can be

– Overhead– Underground

Power lines and transmission towers

Underground Utility Work

Background (cont)• Some activities may cause

interference with power lines– Overhead power lines

• Operation of a crane, forklift, and other construction equipment

• Changing street lights• Tree trimming

– Underground power lines• Excavation

Caution: Look out for overhead power lines when

operating equipment

Types of Electrical Lines• Electrical Cables

– High Voltage, Low Voltage– Supervisory and Signaling Cables– Cathodic protection (cabinets, cables, earthing

conductors, cable shrouds)• Communication Cables

– Phone lines– Coaxial cables (e.g. data cables)– Broadband cables– Tram traction cables and trolley wires– Railway supply cables and traction wires

Power Line HazardsWho is at risk?• Almost everyone working

near power lines• Common hazards:

– Electrocution• Injuries are typically fatal

– Electrical shock– Fires– Falls

• As a result of contact with electricity

Fire may be caused after overhead power lines are hit

When unloading materials, watch out for overhead power lines

Common Misconceptions• Birds land on power

lines, so they must be safe to touch - NO– Main objective of

electricity is to reach the ground using the most direct route

– Birds do not get electrocuted when they land on wires because they do not represent a path to the ground

The power lines are safe for perching, but not when struck

Common Misconceptions• Power lines are insulated, so they are safe to touch - NO

– They are not always insulated• Insulation deals with placing nonconductive material around the wire • Insulation is a material that offers high electric resistance making it

suitable for covering wires to prevent the possible future contact of adjacent conductors resulting in a short circuit

– Just because a wire is weather protected does not mean that it is insulated

• Weather protection prevents water and snow from reaching the wire (and insulation, if used)

Common Misconceptions (Cont)• Nonmetallic ladders are safe around power

lines - NO– Wet ladders can be a conducting medium for

electricity• If power lines are not touched, they are

safe - NO– Electricity can jump

Maintain a safe distance from the Danger Zone

(10 foot radius from the power line)

Hazard Identification• Conduct site investigation to identify

existing conditions of:– Voltages of lines and equipment– Presence of hazardous, induced voltages– Presence and condition of protective

grounds and equipment grounding conductors

– Locations of electrical circuits and equipment

– Maximum switching transient voltages

Dump truck operators should use caution when unloading materials near overhead power lines

Injury Prevention Techniques• Stay away from power

lines while working• Maintain a safe

distance– OSHA’s “10-Foot

Circle of Safety” rule– Increase safe distance

near higher voltage power lines

Maintain a safe distance from the

Danger Zone (10 foot radius from the power line)

Nominal Voltage Minimum Required Distance (Feet)

0 to 50,000 10

Over 50,000 10+0.4 inch for each 1,000 volt

Operation Clearances for Energized Overhead Lines

Nominal Voltage Minimum Required Distance (Feet)

0 to 50,000 4

50,000 to 345,000 10

Over 345,000 to 750,000

16

“In Transit” Clearances for Energized Overhead Lines

Source: OSHA

Injury Prevention Techniques• Recognize high voltage

power lines– If unknown, the

appropriate agency should be contacted

• Inform others about high-voltage power lines Be aware of nearby high-

voltage power lines

Injury Prevention Techniques• Examine the site

– Be mindful of power lines• Search carefully around the site• Look for lines not seen due to

obstructions• Alert others at the pre-job briefing• Assume all lines are energized and

potentially dangerous• Make a safety clearance boundary

– Portable safety barriers

HAZARD:

Safe distance has not been maintained

Injury Prevention• Use a spotter

– Equipment operators have limited visibility

– Get spotter’s help to stay clear of overhead power lines

• Spotter’s job should only require spotting and NOT guiding

– Guiders may be at risk of electrical shock

• Especially when using a tag line

A spotter guiding heavy equipment operator

Injury Prevention

• When working with tall and long equipment– Carefully plan and organize work

with heavy equipment– Keep vehicles clear of power

lines– Watch out for long objects– Adjust the position of equipment

to maintain a safe distance from power lines

Working with tall equipment

Injury Prevention• In cases of fallen

power lines– Stay away– Call for help– Shuffle with your

feet together and on the ground to minimize electrical shock

– Encourage others to do the same

Down power lines are dangerous

Injury Prevention• Fallen power lines can cause fires

• If a co-worker makes contact with a power line– Stay away– Protect yourself

• You could be shocked too if you touch someone who is in contact with electricity

Fire caused by fallen power line

Injury Prevention

• If you hit a power line– In case of no immediate

danger• Move the equipment away• Have someone call 911• Stay on the equipment until

you know it is safe.• Warn others to stay away

– If you MUST get off the equipment, jump clear Crane hitting a power line

Underground Power Lines• Hitting a buried power, gas or

communications line can cause– Injury– Excessive cost of repair

• Plan the work ahead• Call the utility company

With proper planning, these types of mistakes can be avoided

Underground Power Lines• Locate and mark the

perimeter of underground lines

• Exercise caution when excavating near power lines Some manual excavation

may be required• Stay away from pad mount

transformers– Green metal box

Underground utility line that has been hit

Tree Trimming

• Trees that grow into power lines can cause unnecessary power outages

• Trees planted under or near power lines are potentially dangerous hazards

• Before tree trimming, check for the power lines

• Use proper equipment and trained personnel Tree trimming may be dangerous

if power lines are hidden in the foliage

Applicable Standards• 29 CFR 1926, Subpart K – Electrical • 29 CFR 1926, Subpart N – Cranes, Derricks• 29 CFR 1926, Subpart O – Motor Vehicles, Mechanized

Equipment• 29 CFR 1926, Subpart P – Excavations • 1926.416 Electrical Hazards• 1926.955 Overhead Lines• 1926.956 Underground Lines

Summary of the Module• Working in proximity of overhead and

underground power lines is hazardous– Most common hazard is electrocution

• Workers should be aware of such hazards• Several injury prevention techniques should be

exercised to prevent injuries and fatalities– Need sufficient training to understand the hazards

and practices for injury prevention– One of the best ways of hazard elimination is

maintain a minimum safe distance• Properly locate underground power lines before

starting of work