Course 615 Electrical Safety - Hazards and Controls

Recognizing Hazards

Inadequate Wiring Hazards

Look for wiring hazards.
OSHA inspects for inadequate wiring.

Inadequate or improper electrical wiring was one of OSHA's top 10 most commonly cited violations during 2016. An electrical wiring hazard exists when:

  • the wire is too small for the current it will carry: could cause a fire, or
  • is not connected properly: could cause a shock hazard.

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 and 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.

1. In which situation below may an electrical wiring fire hazard exist?

a. When the wire is not rated for the voltage it will carry
b. When the wire is not the proper length for the current it will carry
c. When the wire is too small for the current it will carry
d. When the wire is to large and is inherently too resistant
Protect against electrical hazards
Exposed electrical parts.

Exposed Electrical Parts Hazards

Electrical hazards exist when wires or other live electrical parts are exposed.

  • 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, or equipment that is being service, may have exposed electrical parts.
  • If you contact exposed live electrical parts, you will be shocked.

You must recognize that an exposed electrical component is a hazard.

Real-Life Scenario

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.

2. Exposed live electrical parts may occur in any of the following situations, except _____.

a. overhead wires coming into the home from overhead power lines
b. electrical terminals in locked out and enclosed equipment
c. wiring, if a cover is removed from a breaker
d. terminals in motors, appliances, and equipment

Approach Boundaries

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).

Arc Boundaries
The risk from exposed live parts depends on your distance from the parts.
  1. The Restricted Approach Boundary. This is the closest boundary to exposed live parts. Only a Qualified Person wearing appropriate PPE, as determined by the Shock Risk Assessment, may enter. The Qualified Person must also have an Energized Electrical Work Permit (EEWP). When you're this close, if you move the wrong way, you and your tools could touch live parts.
  2. The Limited Approach Boundary. An Unqualified Person may enter this area, but only if continuously supervised and escorted by a Qualified Person, and advised of potential hazards. Both persons must wear appropriate PPE as determined by the Shock Risk Assessment. A qualified person is someone who has demonstrated the skills and knowledge on the hazards and on the construction and operation of equipment involved in a task.
  3. The Arc Flash Boundary. Only Persons wearing appropriate PPE for the Arc Flash Boundary, as determined by an Arc Flash Risk Assessment, may enter.

3. Only an electrical Qualified Person wearing appropriate PPE, as determined by the Shock Risk Assessment, may enter _____.

a. the Arc Blast Zone
b. the Arc Flash Boundary
c. the Limited Approach Boundary
d. the Restricted Approach Boundary

Overload Hazards

Scope of 1910.1200
Watch out for 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 a 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.

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 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.

4. Which of the following is TRUE about circuit breakers and fuses?

a. Circuit breakers are more reliable than fuses
b. Circuit breakers will melt and fuses will open
c. Both circuit breakers and fuses open the circuit
d. Fuses must always be located near a circuit breaker
Inadeuqate insulation
Inadequate insulation caused a short and fire.

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 and with people.

Extension cords: 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.

Tools: 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.

5. While working with electric hand tools, when are you more likely to receive a shock?

a. If the tool is not grounded or double-insulated
b. If the tool was made prior to 1989
c. When the tool has synthetic insulation
d. When a tool is used while wearing leather gloves

Next Section

Improper Grounding Hazards

Scope of 1910.1200
Proper grounding is important.

When an electrical system is not grounded properly, a hazard exists because unwanted voltage cannot be safely eliminated. 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. 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 an improperly grounded electrical system is a hazard.

6. What is the most common OSHA electrical violation?

a. Defective power tools
b. Failure to use GFCIs on worksites
c. Use of three-prong plugs with power tools
d. Improper grounding of equipment and circuitry

Next Section

Ground Fault Circuit Interrupters (GFCI)

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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 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.

7. Ground Fault Circuit Interrupters (GFCIs) detect the loss of current resulting from _____.

a. a disconnected ground wire in the circuit
b. leakage through a person who is beginning to be shocked
c. short circuits directly to ground
d. an open circuit due to a person not properly grounded

Overhead Powerline Hazards

Scope of 1910.1200
Working near overhead power lines is very dangerous.

Most people do not realize that overhead powerlines are usually not insulated. More than half of all electrocutions are caused by direct worker contact with energized powerlines. Powerline workers must be especially aware of the dangers of overhead lines.

In the past, 80% of all lineman deaths were caused by contacting a live wire with a bare hand. Due to such incidents, all linemen now wear special rubber gloves that protect them up to 34,500 volts. Today, most electrocutions involving overhead powerlines are caused by failure to maintain proper work distances.

Shocks and electrocutions occur where physical barriers are not in place to prevent contact with the wires. When dump trucks, cranes, work platforms, or other conductive materials (such as pipes and ladders) contact overhead wires, the equipment operator or other workers can be killed.

If you do not maintain required clearance distances from powerlines, you can be shocked and killed. (The minimum distance for voltages up to 50kV is 10 feet. For voltages over 50kV, the minimum distance is 10 feet plus 4 inches for every 10 kV over 50kV.) Never store materials and equipment under or near over-head powerlines. We'll talk more about this topic in the next section.

8. In the past, what has been the major cause of all lineman deaths due to electrocution?

a. Touching the live wire with a bare hand
b. Falling across a live wire at elevation
c. Unintentionally contacting some part of the body with a live wire
d. Completing the circuit between two live wires

Minimum Approach Distances

Scope of 1910.1200
Minimum Approach Distance.
Altitude Correction Factor for Minimum Approach Distances. Minimum approach distances ensure that workers do not approach or take any conductive object closer to the energized parts. If the work is performed at elevations greater than 3,000 ft (900m) above mean sea level, the minimum approach distance must be determined by multiplying the distances by the correction factor corresponding to the altitude at which the work is performed.

Depending on the voltage of the line, a worker or a conductive object, must keep the minimum distance specified below between them and any energized part of the power line.

For more information on minimum approach distances and evaluating work zones, see Oregon OSHA's Fact Sheet on Power Line Safety.

See 29 CFR 1910.269 Tables R-3 through R-9 for more information on calculating approach distances.

9. Which of the factors below will increase the safe distance (phase to ground exposure) from a high voltage line?

a. Decrease in humidity
b. Increase in humidity
c. Decrease in altitude
d. Increase in altitude

Next Section

General Indicators of Electrical Hazards

Scope of 1910.1200
Where there is smoke, there is fire.

There are a number of general situations and conditions in the workplace that indicate electrical hazards:

  • Tripped circuit breakers and blown fuses show that too much current is flowing in a circuit. This condition could be due to several factors, such as malfunctioning equipment or a short between conductors. You need to determine the cause in order to control the hazard.
  • An electrical tool, appliance, wire, or connection that feels warm may indicate too much current in the circuit or equipment. You need to evaluate the situation and determine your risk.
  • An extension cord that feels warm may indicate too much current for the wire size of the cord. You must decide when action needs to be taken.
  • A cable, fuse box, or junction box that feels warm may indicate too much current in the circuits.
  • A burning odor may indicate overheated insulation.
  • Worn, frayed, or damaged insulation around any wire or other conductor is an electrical hazard because the conductors could be exposed. Contact with an exposed wire could cause a shock. Damaged insulation could cause a short, leading to arcing or a fire. Inspect all insulation for scrapes and breaks. You need to evaluate the seriousness of any damage you find and decide how to deal with the hazard.
  • A GFCI that trips indicates there is current leakage from the circuit. First, you must decide the probable cause of the leakage by recognizing any contributing hazards. Then, you must decide what action needs to be taken.

10. Tripped circuit breakers and blown fuses show that _____.

a. the speed of the current in the circuit is too fast
b. the resistance in the circuit has increased
c. there has been a spike in voltage
d. too much current is flowing in a circuit

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

Video

This is an excellent electrical presentation by Rodney Sherman given at Holy Cross Energy. It will make a believer out of you.

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