Skip Navigation

Course 715 - Electrical Safety for Technicians & Supervisors

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

Recognizing Hazards

Introduction

The first step toward protecting yourself is recognizing the many hazards you face on the job. To do this, you must know which situations can place you in danger. Knowing where to look helps you to recognize hazards.

  • Inadequate wiring is dangerous
  • Exposed electrical parts are dangerous.
  • Overhead powerlines are dangerous.
  • Wires with bad insulation can shock you.
  • Electrical systems and tools that are not grounded or double-insulated are dangerous.
  • Overloaded circuits are dangerous.
  • Damaged power tools and equipment are electrical hazards.
  • Using the wrong PPE is dangerous.
  • Using the wrong tool is dangerous.
  • Some on-site chemicals are harmful.
  • Defective ladders and scaffolding are dangerous
  • Ladders that conduct electricity are dangerous.
  • Electrical hazards can be made worse if the worker, location, or equipment is wet.

Case Study

An electrician was removing a metal fish tape from a hole at the base of a metal light pole. (A fish tape is used to pull a wire through a conduit run.) The fish tape became energized, electrocuting him. As a result of its inspection, OSHA issued a citation for three serious violations of the agency’s construction standards.

If the following OSHA requirements had been followed, this death could have been prevented.

  • De-energize all circuits before beginning work.
  • Always lock out and tag out de-energized equipment.
  • Companies must train workers to recognize and avoid unsafe conditions associated with their work.

1. All of the following are examples of hazardous situations when working with electricity EXCEPT _____.

a. exposed electrical parts
b. dry or low humidity work conditions
c. working on metal ladders
d. ungrounded electrical systems and tools

Next Section

Inadequate Wiring Hazards

An electrical wiring hazard exists when the wire is too small for the current it will carry or is not connected properly. Normally, the circuit breaker in a circuit is matched to the wire size. However, in older wiring, branch lines to permanent ceiling light fixtures could be wired with a smaller gauge than the supply cable. Let's say a light fixture is replaced with another device that uses more current. The current capacity (ampacity) of the branch wire could be exceeded. When a wire is too small for the current it is supposed to carry, the wire will heat up. The heated wire could cause a fire.

When you use an extension cord, the size of the wire you are placing into the circuit may be too small for the equipment. The circuit breaker could be the right size for the circuit but not right for the smaller-gauge extension cord. A tool plugged into the extension cord may use more current than the cord can handle without tripping the circuit breaker. The wire will overheat and could cause a fire.

The kind of metal used as a conductor can cause an electrical hazard. Special care needs to be taken with aluminum wire. Since it is more brittle than copper, aluminum wire can crack and break more easily. Connections with aluminum wire can become loose and oxidize if not made properly, creating heat or arcing.

You must recognize that inadequate wiring is a hazard.

Case Study

A worker was attempting to correct an electrical problem involving two non-operational lamps. He examined the circuit in the area where he thought the problem was located. He had not shut off the power at the circuit breaker panel and did not test the wires to see if they were live. He was electrocuted when he grabbed the two live wires with his left hand. He collapsed to the floor and was found dead.

If the following OSHA requirements had been followed, this death could have been prevented.

  • Employers should not allow work to be done on electrical circuits unless an effective lock-out/tag-out program is in place.
  • No work should be done on energized electrical circuits. Circuits must be shut off, locked out, and tagged out. Even then, you must test the circuit before beginning work to confirm that it is de-energized ("dead").

2. Electrical wiring may become hazardous and cause arcing or fires if the wires _____.

a. have too much insulation
b. are too long for the load
c. are too small for the load
d. do not have in-line GFCIs

Next Section

This hand held sander has exposed wires and should not be used

Exposed Electrical Parts Hazards

Electrical hazards exist when wires or other electrical parts are exposed. If you contact exposed live electrical parts, you will be shocked.

  • Wires and parts can be exposed if a cover is removed from a wiring or breaker box.
  • The overhead wires coming into a home may be exposed.
  • Electrical terminals in motors, appliances, and electronic equipment may be exposed.
  • Older equipment may have exposed electrical parts.

Guarding. Guarding involves locating or enclosing electric equipment to make sure people don't 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 it is accessible only to authorized people qualified to work with it. Recommended guarding solutions include:

  • A room, vault, or similar enclosure
  • A balcony, gallery, or elevated platform
  • A site elevated 8 feet (2.44 meters) or more above the floor
  • A sturdy, permanent screen

Warning. Conspicuous signs must be posted at the entrances to electrical rooms and similarly guarded locations to alert people to the electrical hazard and to forbid entry to unauthorized people. Signs may contain the word "Danger," "Warning," or "Caution," and beneath that, appropriate concise wording that alerts people to the hazard or gives an instruction, such as "Danger/High Voltage/Keep Out."

3. Effective guarding requires equipment with exposed parts operating at _____ to be placed where it is accessible only to authorized people qualified to work with it.

a. 50 volts or more
b. 120 volts or more
c. 600 volts or more
d. 1000 volts or more

Next Section

Case Study

Five workers were constructing a chain-link fence in front of a house, directly below a 7,200-volt energized power line. As they prepared to install 21-foot sections of metal top rail on the fence, one of the workers picked up a section of rail and held it up vertically. The rail contacted the 7,200-volt line, and the worker was electrocuted. Following inspection, OSHA determined that the employee who was killed never received any safety training from his employer and no specific instruction on how to avoid the hazards associated with overhead power lines.

In this case, the company failed to obey these regulations:

  • Employers must train their workers to recognize and avoid unsafe conditions on the job.
  • Employers must not allow their workers to work near any part of an electrical circuit UNLESS the circuit is de-energized (shut off) and grounded, guarded in such a way that it cannot be contacted.
  • Ground-fault protection must be provided at construction sites to guard against electrical shock.

4. What must be provided at construction sites to guard against electrical shock?

a. OSHA safety bulletin board
b. Ground-fault protection
c. Tested two-prong extension cords
d. Leather or other fabric gloves

Next Section

Approach Boundaries

approach zones
NFPA/CSA Approach Boundaries
(Click to enlarge)

The risk from exposed live parts depends on your distance from the parts. Three "boundaries" are key to protecting yourself from electric shock and one to protect you from arc flashes or blasts. These boundaries are set by the National Fire Protection Association (NFPA 70E-2015) and the Canadian Standards Association (CSA Z462).

  1. The Restricted Approach Boundary . This boundary may only be crossed by a Qualified Person wearing appropriate PPE, as determined by the Shock Risk Assessment.
    • The Qualified Person must also have an Energized Electrical Work Permit (EEWP).
    • The use of shock protection techniques and equipment are required.
    • To cross into the Restricted Space, the qualified person must wear appropriate PPE.
    • The Qualified Person must have a written approved plan for the work to be performed and plan the work to keep all parts of the body out of the Prohibited Space.
  2. The Limited Approach Boundary. NFPA 70 defines the limited approach boundary as a shock protection boundary to be crossed by only qualified persons (at a distance from a live part), which is not to be crossed by unqualified persons unless escorted by a qualified person.
    • This boundary is the minimum distance from the energized item where unqualified personnel may safely stand.
    • No untrained personnel may approach any closer to the energized item than this boundary.
    • A qualified person must use appropriate PPE and be trained to perform the required work to cross the limited approach boundary and enter the limited space.
  3. Flash Protection Boundary (FPB). The FPB is the farthest established boundary from the energy source and is considered a safe approach distance from energized equipment or parts.
    • Only Persons wearing appropriate personal protective clothing and equipment for the Arc Flash Boundary, as determined by an Arc Flash Risk Assessment, may approach closer than the FPB.

5. When working around high voltage components, no untrained personnel may approach any closer to the energized item than the _____.

a. Prohibited Approach Boundary
b. Restricted Approach Boundary
c. Limited Approach Boundary
d. Flash Protection Boundary

Next Section

Overhead Powerline Hazards

Overhead power lines are not insulated and can carry tens of thousands of volts, making them extremely dangerous to employees who work in their vicinity. Powerline workers must be especially aware of the dangers of overhead lines.

More than half of all electrocutions are caused by direct worker contact with energized powerlines because workers fail to maintain proper work distance. Fatal electrocution is the main risk, but burns and falls from elevations are also hazards. Using tools and equipment that can contact power lines increases the risk.

Examples of equipment that can contact overhead power lines include:

  • Aluminum paint rollers
  • Backhoes
  • Concrete pumpers
  • Cranes
  • Long-handled cement finishing floats
  • Metal building materials
  • Metal ladders
  • Raised dump truck beds
  • Scaffolds

Avoid overhead power line hazards by following these best practices:

  • Look for overhead power lines and buried power line indicators. Post warning signs.
  • Contact utilities for buried power line locations.
  • Stay at least 10 feet away from overhead power lines.
  • Unless you know otherwise, assume that overhead lines are energized.
  • De-energize and ground lines when working near them. Other protective measures include guarding or insulating the lines.
  • Use non-conductive wood or fiberglass ladders when working near power lines.
photo29

(Click to enlarge)
photo31

(Click to enlarge)
photo26

(Click to enlarge)

6. What is the cause of more than half of all electrocutions?

a. Direct worker contact with energized powerlines
b. Improper transformer wiring
c. Defective power tools
d. Improperly grounded equipment

Next Section

photo32

Defective Insulation Hazards

Insulation that is defective or inadequate is an electrical hazard. Usually, a plastic or rubber covering insulates wires. Insulation prevents conductors from coming in contact with each other. Insulation also prevents conductors from coming in contact with people.

Extension cords may have damaged insulation. Sometimes the insulation inside an electrical tool or appliance is damaged. When 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. If you touch damaged power tools or other equipment, you will receive a shock. You are more likely to receive a shock if the tool is not grounded or double-insulated. (Double-insulated tools have two insulation barriers and no exposed metal parts.)

You must recognize that defective insulation is a hazard.

Improper Grounding Hazards

When an electrical system is not grounded properly, a hazard exists. The most common OSHA electrical violation is improper grounding of equipment and circuitry. The metal parts of an electrical wiring system that we touch (switch plates, ceiling light fixtures, conduit, etc.) should be grounded and at 0 volts. If the system is not grounded properly, these parts may become energized. Metal parts of motors, appliances, or electronics that are plugged into improperly grounded circuits may be energized. When a circuit is not grounded properly, a hazard exists because unwanted voltage cannot be safely eliminated. If there is no safe path to ground for fault currents, exposed metal parts in damaged appliances can become energized.

Extension cords may not provide a continuous path to ground because of a broken ground wire or plug. If you contact a defective electrical device that is not grounded (or grounded improperly), you will be shocked.

You must recognize that an improperly grounded electrical system is a hazard.

7. Double-insulated equipment must meet which of the following two criteria?

a. Two safety switches, guarded parts
b. Two insulation barriers, no exposed parts
c. No insulation barriers, two exposed parts
d. No exposed parts or insulation barriers

Next Section

Ground Fault Circuit Interrupters (GFCI)

photo33

A ground fault circuit interrupter, or GFCI, is an inexpensive life-saver. GFCIs detect any difference in current between the two circuit wires (the black wires and white wires). This difference in current could happen when electrical equipment is not working correctly, causing leakage current. If leakage current (a ground fault) is detected in a GFCI-protected circuit, the GFCI switches off the current in the circuit, protecting you from a dangerous shock. More important points to remember:

  • GFCIs are set at about 5 mA and are designed to protect workers from electrocution.
  • GFCIs are able to detect the loss of current resulting from leakage through a person who is beginning to be shocked. If this situation occurs, the GFCI switches off the current in the circuit.
  • GFCIs are different from circuit breakers because they detect leakage currents rather than overloads.

Circuits with missing, damaged, or improperly wired GFCIs may allow you to be shocked.

You need to recognize that a circuit improperly protected by a GFCI is a hazard.

8. GFCIs detect any difference in _____ between the two circuit wires (the black wires and white wires).

a. impedance
b. voltage
c. current
d. resistance

Next Section

Overloading leads to overheating of circuit components (including wires) and may cause a fire.
Overloading leads to overheating of circuit components (including wires) and may cause a fire.

Overload Hazards

Overloads in an electrical system are hazardous because they can produce heat or arcing. Wires and other components in an electrical system or circuit have a maximum amount of current they can carry safely. If too many devices are plugged into a circuit, the electrical current will heat the wires to a very high temperature. If any one tool uses too much current, the wires will heat up.

The temperature of the wires can be high enough to cause a fire. If their insulation melts, arcing may occur. Arcing can cause a fire in the area where the overload exists, even inside a wall.

In order to prevent too much current in a circuit, a circuit breaker or fuse is placed in the circuit. If there is too much current in the circuit, the breaker "trips" and opens like a switch. If an overloaded circuit is equipped with a fuse, an internal part of the fuse melts, opening the circuit. Both breakers and fuses do the same thing: open the circuit to shut off the electrical current.

If the breakers or fuses are too big for the wires they are supposed to protect, an overload in the circuit will not be detected and the current will not be shut off. Overloading leads to overheating of circuit components (including wires) and may cause a fire.

You must recognize that a circuit with improper overcurrent protection devices-or one with no overcurrent protection devices at all-is a hazard.

Overcurrent protection devices are built into the wiring of some electric motors, tools, and electronic devices. For example, if a tool draws too much current or if it overheats, the current will be shut off from within the device itself. Damaged tools can overheat and cause a fire.

You must recognize that a damaged tool is a hazard.

9. All of the following may happen if the circuit breakers or fuses are too big for the wires they are supposed to protect EXCEPT _____.

a. the circuit may blow a fuse too soon
b. it may cause a fire
c. an overload will not be detected
d. the current may not be shut off

Next Section

Overloading leads to overheating of circuit components (including wires) and may cause a fire.
If you touch a live electrical component with an uninsulated hand tool, you are more likely to receive a shock when standing in water.

Wet Conditions Hazards

Working in wet conditions is hazardous because you may become an easy path for electrical current. For instance, if you touch a live wire while standing in even a puddle of water, you will probably receive a shock.

Damaged insulation, equipment, or tools can expose you to live electrical parts. A damaged tool may not be grounded properly, so the housing of the tool may be energized, causing you to receive a shock. Improperly grounded metal switch plates and ceiling lights are especially hazardous in wet conditions. If you touch a live electrical component with an uninsulated hand tool, you are more likely to receive a shock when standing in water.

Remember: you don't have to be standing in water to be electrocuted. Wet clothing, high humidity, and perspiration also increase your chances of being electrocuted.

You must recognize that all wet conditions are hazards.

Additional Hazards

In addition to electrical hazards, other types of hazards are present at job sites. Remember that all of these hazards can be controlled.

  • There may be chemical hazards. Solvents and other substances may be poisonous or cause disease.
  • Frequent overhead work can cause tendinitis (inflammation) in your shoulders.
  • Intensive use of hand tools that involve force or twisting can cause tendinitis of the hands, wrists, or elbows. Use of hand tools can also cause carpal tunnel syndrome, which results when nerves in the wrist are damaged by swelling tendons or contracting muscles.

10. If you touch a live electrical component with an uninsulated hand tool, you are more likely to receive a shock in all of the following situations EXCEPT _____.

a. when perspiring
b. when wearing wet clothing
c. when working in an open field
d. when standing in water

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.

Video
OSHAcademy Ultimate Guide Banner Ad