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Course 809: Focus Four - Electrocution Hazards

Safety guides and audits to make your job as a safety professional easier

Protection from Electrocution Hazards

Power Line Safety

When cranes and derrick operations are conducted around power lines, the employer must determine if any part of the equipment, load line or load (including rigging and lifting accessories), if operated up to the equipment's maximum working radius in the work zone, could get closer than 20 feet to a power line. If so, the employer must meet one of the following requirements:

  1. De-energize and ground. Confirm from the utility owner/operator that the power line has been de-energized and visibly grounded at the worksite.
  2. 20 foot clearance. Ensure that no part of the equipment, load line, or load (including rigging and lifting accessories), gets closer than 20 feet to the power line by implementing the measures specified in paragraph (b) of this section.
  3. Table A clearance. The minimum clearance distance when working around power lines up to 50kV is 10 feet. Click the button to review 1926.1408, Table A - Minimum Clearance Distances, that lists clearance distances for other power lines voltages.
  4. Table A - Minimum Clearance Distances

    Voltage (nominal, kV, alternating current) Minimum clearance distance (feet)
    Up to 50 10
    Over 50 to 200 15
    Over 200 to 350 20
    Over 350 to 500 25
    Over 500 to 750 35
    Over 750 to 1000 45
    Over 1000 (As established by the power line owner/operator or registered professional engineer who is a qualified person with respect to electrical power transmission and distribution)

The following are preventive measures for workers to consider. Before work begins, make sure:

Crane near powerlines
Always maintain safe clearance distances.
  • equipment/activity is located within a safe working distance from power lines;
  • the utility company has de-energized and visibly grounded the power lines or installed insulated sleeves on power lines;
  • flagged warning lines have been installed to mark horizontal and vertical power line clearance distances; and
  • tools and materials used are nonconductive.

Click the button below to a video on a crane contact electrical accident.

1. What is the minimum clearance distance from a power line rated at to 7.5 kV?

a. 5 feet
b. 10 feet
c. 15 feet
d. 20 feet

Next Section

Power Line Safety (Continued...)

Cranes and other high-reaching equipment. Be sure the utility company has confirmed the voltage and, therefore, the safe working distance from the power lines. Also, if applicable and feasible, use a/an: observer; insulated link; boom cage guard; proximity device.

Mobile heavy equipment. If provided, use installed rider posts under power lines to avoid working too close to the power lines.

Scaffolds. Erecting scaffolds under or next to power lines may cause workers to violate safe clearance distances and expose them to electrocution. Care must be taken to ensure the scaffold does not contact power lines or that workers cannot expose themselves to electrocution while using equipment on the scaffold.

Ladders. Fatalities occur every year due to the use of metallic ladders under power lines. It's easy to forget the locations of power lines when focused on tasks. Therefore, use only nonconductive ladders and be sure to retract them before moving. If it's necessary to use metallic ladders, make sure you retract and carry them horizontally.

Material storage. Ensure no materials are stored under power lines, and use caution tape and signs to cordon off area under power lines.

Excavations. Locate and understand the markings the local underground line locator service has marked before digging. Hand dig within three feet of cable location (be aware that more than one underground cable may be buried in area of locator markings).

Real-World Accident

Let's take a look at a real world accident caused by failing to maintain safe clearance distances.

Crane near powerlines
This boom is 9.5 feet from the power line. Is it too close?

Description of Accident

Employees were moving a steel canopy structure using a crane. The boom cable made contact with a 7.2 kV electrical power distribution line electrocuting the operator of the crane; he was the foreman at the site.

Inspection Results

As a result of its investigation OSHA issued citations for four serious violations of its construction standards dealing with training, protective equipment, and working too close to power lines. OSHA's construction safety standards include several requirements that, if they had been followed here might have prevented this fatality.

What would you recommend?

Recommendations

  • Develop and maintain a safety and health program to provide guidance for safe operations (29 CFR1926.20(b)(1))
  • Instruct each employee on how to recognize and avoid unsafe conditions that apply to the work and work areas (29 CFR 1926.21(b)(2))
  • If high voltage lines are not de-energized, visibly grounded, or protected by insulating barriers, equipment operators must maintain a minimum distance of 10 feet between their equipment and the electrical distribution or transmission lines (29 CFR 1926.550(a)(15)(i))

2. Which of the following is necessary when using high-reaching equipment near overhead power lines?

a. Use metal/conductive ladders
b. Hand dig within 10 feet of a cable location
c. Ensure the utility company has confirmed voltages
d. Keep stacked materials under power lines to a minimum

Next Section

Power Line Safety (Continued...)

What Must Your Employer do to Protect You?

Before working on overhead power lines, employers must ensure power lines are de-energized and grounded by the owner/operator of the lines, or other protective methods must be used, such as:

  • electrical personal protective equipment, (insulating gloves, footwear, hoods, sleeves, protective clothing, and hearing protectors);
  • non-conductive ladders and platforms;
  • fall arrest and positioning systems; and
  • other protective equipment (insulator caps, distribution cut-out covers, insulating line hoses, bushing covers, insulating shields, insulating cross-arm covers, and insulating pole wraps) to prevent contact with the lines.
Lineman working on powerlines
Power company installing sleeves over power lines.

Training

Employers must initially train workers upon initial assignment on specific safe work practices, safety procedures, and other safety requirements. Qualified employees must be trained in competent in:

  • the skills and techniques necessary to distinguish exposed live parts from other parts of electric equipment;
  • the skills and techniques necessary to determine the nominal voltage of exposed live parts;
  • the minimum approach distances corresponding to the voltages to which they will be exposed and the skills and techniques necessary to maintain those distances;
  • the proper use of the special precautionary techniques, personal protective equipment, insulating and shielding materials, and insulated tools for working on or near exposed energized parts of electric equipment; and
  • the recognition of electrical hazards to which they may be exposed and the skills and techniques necessary to control or avoid these hazards.

Real-World Accident

Let's take a look at a real world accident caused by failing to maintain safe clearance distances.

Powerline near fence
Always know what above you when working with ladders and poles.

Description of Accident

Five employees were constructing a chain link fence in front of a house and directly below a 7200-volt energized power line. They were installing 21-foot sections of metal top rail on the fence. One employee picked up a 21-foot section of top rail and held it up vertically. The top rail contacted the 7200-volt line, and the employee was electrocuted.

Inspection Results

Following its inspection, OSHA determined the employee who was killed had never received any safety training from his employer nor any specific instruction in avoiding the hazards posed by overhead power lines. The agency issued two serious citations for the training deficiencies.

What would you recommend?

Recommendations

  1. Employers must instruct employees to recognize and avoid unsafe conditions applicable to their work environment - 29 CFR 1926.21(b)(2).
  2. Employers must not permit employees to work in proximity to any part of an electrical power circuit when the employee could contact it during the course of work, unless the employee is protected against electric shock by de-energizing the circuit and grounding it or by guarding it effectively by insulation or other means - 29 CFR 1910.416(a)(1).

3. Before working on overhead power lines, employees must use _____.

a. conductive shorting bars
b. nonconductive warning signs
c. electrical personal protective equipment
d. type A bump caps

Next Section

Ground Fault Circuit Interrupters

A GFCI is a ground fault circuit interrupter designed to protect people from severe and sometimes fatal electrical shock. A GFCI detects ground faults and interrupts the flow of electric current and is designed to protect the worker by limiting the duration of an electrical shock.

An Example of How a GFCI Works

A homeowner is using an old drill with a loose bare wire inside it touching the outer metal housing. When the drill is plugged in, the housing of the drill is charged with electricity. If it is used outside in the rain and the worker is standing on the ground, there is a path from the hot wire inside the drill through the worker to the ground. If electricity flows from the drill to ground through the worker, it could be fatal. GFCIs monitor the current-to-the load for leakage to ground. When this leakage exceeds 5 mA + 1 mA, the GFCI interrupts the current, trips the circuit, and cuts off the electricity.

Click the button to see a video explaining how GFCIs work.

Click the button below to review an accident caused improper GFCI safety.

Ladder on scaffolding
Metal ladder on scaffold. A missing ground prong caused a fatality.

Description of Accident

One employee was climbing a metal ladder to hand an electric drill to the journeyman installer on a scaffold about five feet above him. When the victim reached the third rung from the bottom of the ladder, he received an electric shock that killed him. The investigation revealed that the extension cord had a missing grounding prong and that a conductor on the green grounding wire was making intermittent contact with the energizing black wire thereby energizing the entire length of the grounding wire and the drill's frame. The drill was not double insulated.

Inspection Results

As a result of its investigation, OSHA issued citations for violations of construction standards.

What would you recommend?

Recommendations

  • Use approved ground fault circuit interrupters (GFCI) or an assured equipment grounding conductor program to protect employees on construction sites [29 CFR 1926.404(b)(1)].
  • Use equipment that provides a permanent and continuous path from circuits, equipment, structures, conduit or enclosures to ground [29 CFR 1926.404(d)(6)].
  • Inspect electrical tools and equipment daily and remove damaged or defective equipment from use until it is repaired [29 CFR 1926.404(b)(iii)(c)].

4. A GFCI protects the worker by _____.

a. increasing the lag time for disconnection
b. limiting the duration of an electrical shock
c. improving the quality of current connections
d. decreasing voltage and current ratings

Next Section

Receptacle GFCI
Receptacle GFCI

Types of GFCI

Receptacle GFCI: Often found on construction work sites, outdoor areas and other locations where damp conditions do or could exist. The receptacle GFCI fits into the standard outlet box and protects users against ground faults when an electrical product is connected to the GFCI protected outlet.

These should be tested after installation and once a month by:

  • Plug in a test light or power tool and turn "On."
  • Push the "Test" button on the receptacle; the "Test" button should pop up, and the power to the light or tool should be "Off."
  • Push "Reset" to restore power to the outlet.
  • If the above steps worked, the GFCI passed the test and is functioning properly; if the GFCI failed the test, remove it from service.
Portable GFCI
Portable GFCI

If a light or power tool remains "ON" when the "Test" button is pushed, the GFCI is not working properly or has been incorrectly installed (miswired). If this is the case, a qualified electrician needs to be contacted to properly wire or replace the GFCI device.

Portable/Temporary GFCI: A portable GFCI is an extension cord combined with a GFCI. It adds flexibility in using receptacles that are not protected by GFCIs. Extension cords with GFCI protection incorporated should be used when permanent protection is unavailable.

These should be tested prior to each and every use by:

  • visually inspecting the device for obvious defects and/or broken parts;
  • plugging in a test light/tool to the extension cord;
  • pushing the "Reset" button on the GFCI device;
  • pushing the "Test" button to verify no voltage at outlet (e.g., the light or tool shuts off); and
  • pushing the "Reset" button to verify the power is restored.

5. Which devices should be tested at least once a month on a construction site?

a. All pneumatic tools
b. Portable extension cords
c. Site lighting circuits
d. Receptacle GFCIs

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Types of GFCI (Continued)

Test light/tool
Circuit Breaker GFCI - Eaton

Circuit Breaker GFCI: The GFCI circuit breaker controls an entire circuit and is installed as a replacement for a circuit breaker on the main circuit board. Rather than install multiple GFCI outlets, one GFCI circuit breaker can protect the entire circuit. At sites equipped with circuit breakers, this type of GFCI might be installed in a panel box to give protection to selected circuits.

Circuit breaker GFCIs should be tested monthly. Keep in mind that the test will disconnect power to everything on the circuit.

Employer Responsibilities

OSHA ground-fault protection rules and regulations have been determined necessary and appropriate for worker safety and health. It is your employer's responsibility to provide either:

  • GFCIs on construction sites for receptacle outlets in use and not part of the permanent wiring of the structure; or
  • a scheduled and recorded assured equipment grounding conductor program on construction sites.

6. Which type of GFCI controls an entire electrical circuit?

a. Circuit breaker GFCI
b. Receptacle GFCI
c. Portable GFCI
d. Main GFCI

Next Section

Assured Equipment Grounding Conductor Program (AEGCP)

The AEGCP covers all cord sets, receptacles that are not a part of the permanent wiring of the building or structure, and equipment connected by cord and plug that are available for use or used by employees. OSHA requires a written description of the employer's AEGCP, including the specific procedures adopted, be kept at the job site. This program should outline the employer's specific procedures for the required equipment inspections, tests, and test schedule.

The required tests must be recorded, and the record maintained until replaced by a more current record. The written program description and the recorded tests must be made available, at the job site, to OSHA and any affected employee upon request. The employer is required to designate one or more competent persons to implement the program.

Portable GFCI
Employers need to ensure electrical equipment is visually inspected for damage before each day’s use.

Electrical equipment noted in the AEGCP must be visually inspected for damage or defects before each day's use. The employee must not use any damaged or defective equipment until it is repaired.

OSHA requires two tests:

  1. Continuity Test: The continuity test ensures that the equipment grounding conductor is electrically continuous. Perform this test on all cord sets, receptacles that are not part of a building or structure's permanent wiring, and cord- and plug-connected equipment required to be grounded. This test can be accomplished with various test equipment.
  2. Terminal Connection Test: The terminal connection test ensures that the equipment grounding conductor is connected to its proper terminal at receptacles and cord plugs. Perform this test with the same equipment used in the first test, or for receptacles use receptacle testers.

7. Which test is required by OSHA in the Assured Equipment Grounding Conductor Program (AEGCP)?

a. Secondary Connection Test
b. Maximum Voltage Test
c. Main Circuit Test
d. Continuity Test

Next Section

Inspect Portable Tools and Extension Cords

Wire size and ampacity

The OSHA construction standard requires flexible cords to be rated for hard or extra-hard usage. These ratings are derived from the National Electrical Code, and your employer is required to make sure the cord is indelibly marked approximately every foot along the length of the cord.

Workers need to inspect extension cords prior to their use for any cuts or abrasion. Extension cords may have damaged insulation. Sometimes the insulation inside an electrical tool or appliance is damaged. When the insulation is damaged, exposed metal parts may become energized if a live wire inside touches them. Electric hand tools that are old, damaged, or misused may have damaged insulation inside. You can click the following links to review toolbox talk 2 and toolbox talk 3.

Flexible cords used with temporary and portable lights must be designed for hard or extra-hard usage. They must be marked with usage type designation size and number of conductors. The cord could be marked with a 14/3 meaning the conductor size (AWG) is 14, and the number of conductors is 3.

Extension cords must be 3-wire type so they may be grounded, and able to permit grounding of any tools or equipment connected to them.

Limit exposure of connectors and tools to excessive moisture by using watertight or sealable connectors.

Wire Size and Ampacity

In terms of conducting electrical current, size matters (the size of the electrical conductor). Click on the button below and look at the table regarding ampacity, the current-carrying capacity of a conductor in amps. You'll notice two things: the amount of current a wire can safely carry increases as the diameter (and area) of the wire increases and as the number of the wire size decreases.

AWG Copper Wire Table

Copper Wire Size (AWG) Diameter(Mils) Area (Circular mils) Ampacity in Free Air Ampacity as Part of 3-conductor Cable
14 AWG 64.1 4109 20 Amps 15 Amps
12 AWG 80.8 6529 25 Amps 20 Amps
10 AWG 101.9 10,384 40 Amps 30 Amps
8 AWG 128.5 16,512 70 Amps 50 Amps

Click the buttons below to videos on a crane contact electrical cables and cords.

8. The cord marked as 14/3 means _____.

a. the conductor size is 14 and has 3 wires
b. the conductor length is 14 and 3 cm in diameter
c. the cord has 3-prong plug every 14 feet
d. the cord is rated for 14 amps at 3 ohms resistance

Next Section

Using Power Tools and Equipment

Power cords laying all over the floor of a house under construction.
Are these cords a tripping hazard?

Workers using power tools and equipment should follow tool safety tips to avoid misusing equipment.

  • Never carry a tool by the cord.
  • Never yank the cord to disconnect it.
  • Ensure cords do not cause a tripping hazard.
  • Keep cords away from heat, oil, and sharp edges.
  • Disconnect tools when not in use and when changing accessories such as blades and bits.
  • Do not hold fingers on the switch button while carrying a plugged-in tool.
  • Use gloves and appropriate footwear.
  • Store tools in a dry place when not using.
  • Don't use tools in wet/damp environments.
  • Keep working areas well lit.
  • Remove damaged tools from use.
  • Use double-insulated tools.

Click the buttons below to see some common examples of misusing equipment.

Power cord missing the ground prong.
The ground prong must never be removed from the plug.
  • using multi-receptacle boxes designed to be mounted by fitting them with a power cord and placing them on the floor
  • fabricating extension cords with ROMEX wire
  • using equipment outdoors that is labeled for use only in dry, indoor locations
  • attaching ungrounded, two-prong adapter plugs to three-prong cords and tools
  • using circuit breakers or fuses with the wrong rating for over-current protection (e.g., using a 30-amp breaker in a system with 15 or 20 amp receptacles - protection is lost because it will not trip when the system's load has been exceeded)
  • using modified cords or tools (i.e., ground prongs removed, face plates, insulation, etc.)
  • using cords or tools with worn insulation or exposed wires

Workers need to know even when the power system is properly grounded, electrical equipment can instantly change from safe to hazardous because of extreme conditions and rough treatment.

What Must Your Employer do to Protect You?

Your employer needs to ensure all power tools and equipment are maintained in a safe condition to:

  • ground power supply systems, electrical circuits, and electrical equipment
  • frequently inspect electrical systems to ensure path to ground is continuous
  • ensure workers understand to inspect electrical equipment prior to use
  • ensure ground prongs are not removed from tools or extension cords
  • ground exposed metal parts of equipment

9. Using a 30-amp breaker in a system with 15 or 20 amp receptacles is not allowed because _____.

a. it does not engage until 20 volts is reached
b. it does not trip until it gets too hot
c. it will not trip when the load has been exceeded
d. it will trip prior too early

Next Section

Lockout/Tagout Procedures

LOTO tag on electrical box.
Lockout/Tagout protects against unexpected startup.

Lockout/tagout is an essential safety procedure to protect workers from injury while working on or near electrical circuits and equipment. In addition, lockout/tagout prevents contact with operating equipment parts such as blades, gears, shafts, etc. Also, lockout/tagout prevents the unexpected release of hazardous gases, fluids, or solid matter in areas where workers are present.

To protect against being electrocuted, workers need to follow lockout/tagout procedures. If performing lockout/tagout on circuits and equipment, you may use the following checklist.

  • Identify all sources of electrical energy for the equipment or circuits in question.
  • Disable backup energy sources such as generators and batteries.
  • Identify all shut-offs for each energy source.
  • Notify all personnel equipment and circuitry must be shut off, locked out, and tagged out (simply turning a switch off is not enough).
  • Shut off energy sources and lock switch gear in the OFF position. Each worker should apply his/her individual lock and keys kept with the worker.
  • A qualified person must test equipment and circuitry to make sure they are de-energized.
  • Deplete stored energy (for example, in capacitors) by bleeding, blocking, grounding, etc.
  • Apply a lock or tag to alert other workers that an energy source or piece of equipment has been locked or tagged out.
  • Make sure all workers are safe and accounted for before equipment and circuits are unlocked and turned back on. Only a qualified person may determine when it is safe to re-energize circuits.

Only qualified persons may work on electric circuit parts or equipment that has not been de-energized. Such persons must be capable of working safely on energized circuits and must be familiar with the proper use of special precautionary techniques, PPE, insulating and shielding materials, and insulated tools.

Real-World Accident

Let's take a look at a couple of a real world accident and a video about failures to follow lockout/tagout procedures.

Lightpole with electrical maintenance cover open.

Description of Accident

An electrician was removing metal fish tape (a fish tape is used to pull wire through a conduit run) from a hole at the base of a metal light pole. The fish tape became energized, electrocuting him.

Inspection Results

As a result of its inspection, OSHA issued a citation for three serious violations of the agency's construction standards. Had requirements for de-energizing energy sources been followed, the electrocution might have been prevented.

What would you recommend?

Recommendations

  • Ensure all circuits are de-energized before beginning work - 29 CFR 1926.416(a)(3).
  • Controls to be deactivated during the course of work on energized or de-energized equipment or circuits must be tagged - 29 CFR 1926.417(a).
  • Employees must be instructed to recognize and avoid unsafe conditions associated with their work - 29 CFR 1926.21(b)(2).

10. When using lockout/tagout of, be sure to identify _____.

a. voltage circuits above 120 vac
b. all sources of energy
c. proper manufacturer recommendations
d. electrical energy sources

Next Section

Employer Lockout/Tagout Responsibilities

Enforcement. Your employer must enforce LOTO safety-related work practices by ensuring:

  • controls that are to be deactivated during the course of work on energized or de-energized equipment or circuits are locked out, tagged or both;
  • equipment or circuits that are de-energized shall be rendered inoperative and post tags attached at all points where such equipment or circuits can be energized;
  • tags are placed to plainly identify the equipment or circuits being worked on; and
  • all circuits used to energize equipment are locked out/tagged out if any worker is exposed to contact with parts of fixed electric equipment that has been de-energized.
Wire protruding from a wall under construction.
Do you think this electrical wire is protected from abrasion?

Isolation.The employer must ensure electrical parts are properly isolated, and conductors entering boxes, cabinets, or fittings are protected from abrasion. Openings through which conductors enter must be closed. Unused openings in cabinets, boxes, and fittings must also be effectively.

All pull boxes, junction boxes, and fittings must have covers. Metal covers need to be grounded. In energized installations, each outlet box needs to have a cover, faceplate, or fixture canopy. Covers of outlet boxes having holes through which flexible cord pendants pass shall be provided with bushings designed for the purpose or shall have smooth, well-rounded surfaces on which the cords may rest.

Ensure Proper Guarding. Guarding involves locating or enclosing electrical equipment to ensure workers do not accidentally come into contact with its live parts. Effective guarding requires equipment with exposed parts operating at 50 volts or more to be placed where they are accessible only to authorized people qualified to work with/on the equipment.

Training. Workers need be trained in and familiar with the safety-related work practices that pertain to their respective job assignments. Employers should train their employees to:

  • de-energize electric equipment before inspecting or repairing;
  • use cords, cables, and electric tools that are in good repair;
  • know and understand lockout/tagout recognition and procedures; and
  • use appropriate protective equipment.

11. What must your employer do to help protect you from electrical hazards?

a. Ensure electrical parts are properly isolated
b. Allow employees to work around exposed live wiring
c. Shut off all power to the job site while work is being conducted
d. Only hire electricians to perform all work at the job site

Check your Work

Read the material in each section to find the correct answer to each quiz question. After answering all the questions, click on the "Check Quiz Answers" button to grade your quiz and see your score. You will receive a message if you forgot to answer one of the questions. After clicking the button, the questions you missed will be listed below. You can correct any missed questions and check your answers again.

Final Exam