Electrical Safety: Safety & Health for Electrical Trades (Student Manual)

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Summary Statement

Student manual on electrical safety with information on recognizing, evaluating and avoiding hazards related to electricity.
January 2002

Safety Model Stage 1— Recognizing Hazards

How Do You Recognize Hazards?

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 give you a shock.
  • 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.
  • Workers face many hazards on the job.

  • Worker was electrocuted while removing energized fish tape.

    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 wire through a conduit run.) The fish tape became energized, electro-cuting 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.

    Fish Tape.

    Inadequate wiring hazards

    An electrical hazard exists when the wire is too small a gauge for the current it will carry. Normally, the circuit breaker in a circuit is matched to the wire size. However, in older wiring,
    This hand-held sander has
    exposed wires and should not be used.
    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 cur-rent 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 need to recognize that inadequate wiring is a hazard.

  • wire gauge—wire size or diameter (technically, the cross-sectional area)
  • ampacity—the maximum amount of current a wire can carry safely without overheating
  • Overloaded wires get hot!
  • Incorrect wiring practices can cause fires!
  • If you touch live electrical parts, you will be shocked.

  • Exposed electrical parts hazards

    Electrical hazards exist when wires or other 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 may have exposed electrical parts. If you contact exposed live electrical parts, you will be shocked. You need to recognize that an exposed electrical component is a hazard.

    Overhead powerline hazards

    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.

     Overhead powerlines kill many workers!
    Watch out for exposed electrical wires around electronic equipment. Electrical line workers need special training and equipment to work safely.

     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. You need to recognize that overhead powerlines are a hazard.
    Operating a crane near overhead wires is
    very hazardous.

     Five workers were constructing a chain-link fence in front of a house, directly below a 7,200-volt energized powerline. 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 had never received any safety training from his employer and no specific instruction on how to avoid the hazards associated with overhead powerlines.

    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, or guarded in such a way that it cannot be contacted.
    • Ground-fault protection must be provided at construction sites to guard against electrical shock.

    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 need to recognize that defective insulation is a hazard.

     Image of damanged extension cord
    This extension cord is damaged and should not be used.

  • insulation- material that does not conduct electricity easily.
  • If you touch a damaged live power tool, you will be shocked!
  • A damaged live power tool that is not grounded or double-insulated is very dangerous!
  • fault current- any current that is not in its intended path
  • ground potential- the voltage a grounded part should have; 0 volts relative to ground

  • 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 need to recognize that an improperly grounded electrical system is a hazard.

    Electrical systems are often grounded to metal water pipes that serve as a continuous path to ground. If plumbing is used as a path to ground for fault current, all pipes must be made of conductive material (a type of metal). Many electrocutions and fires occur because (during renovation or repair) parts of metal plumbing are replaced with plastic pipe, which does not conduct electricity. In these cases, the path to ground is interrupted by nonconductive material.

    A ground fault circuit interrupter, or GFCI, is an inexpensive life-saver. GFCI's 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. GFCI's are set at about 5 mA and are designed to protect workers from electrocution. GFCI's 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. GFCI's are different from circuit breakers because they detect leakage currents rather than overloads.

    Circuits with missing, damaged, or improperly wired GFCI's may allow you to be shocked. You need to recognize that a circuit improperly protected by a GFCI is a hazard.

    If you touch a defective live component that is not grounded, you will be shocked.
    GFCI—ground fault circuit interrupter—a device that detects current leakage from a circuit to ground and shuts the current off
    leakage current—current that does not return through the intended path but instead "leaks” to ground
    ground fault—a loss of current from a circuit to a ground connection
    overload—too much current in a circuit
    An overload can lead to a fire or electrical shock.

    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.

     Overloads are a major cause
    of fires.

    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 need to 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 need to recognize that a damaged tool is a hazard.

    Damaged equipment can overheat and cause a fire

    circuit breaker—an overcurrent protection device that automatically
    shuts off the current in a circuit if an overload occurs
    trip—the automatic opening (turning off) of a circuit by a GFCI or circuit breaker
    fuse—an overcurrent protection device that has an internal part that melts and shuts off the current in a circuit if there is an overload
    Circuit breakers and fuses that are too big for the circuit are dangerous.
    Circuits without circuit breakers or fuses are dangerous.
    Damaged power tools can cause overloads.
    Wet conditions are dangerous.

    Wet conditions hazards

    Working in wet conditions is hazardous because you may become an easy path for electrical current. If you touch a live wire or other electrical component—and you are well-grounded because you are standing in even a small puddle of water—you will 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.

    But 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 need to recognize that all wet conditions are hazards.

  • An electrical circuit in a damp place without a GFCI is dangerous! A GFCI reduces the danger.
  • There are non-electrical hazards at job sites, too.

  • 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.

     Overhead work can cause long-term shoulder pain.
    Frequent use of some hand tools can cause wrist
    problems such as carpal tunnel syndrome.

    A 22-year-old carpenter’s apprentice was killed when he was struck in the head by a nail fired from a powder-actuated nail gun (a device that uses a gun powder cartridge to drive nails into concrete or steel). The nail gun operator fired the gun while attempting to anchor a plywood concrete form, causing the nail to pass through the hollow form. The nail traveled 27 feet before striking the victim. The nail gun operator had never received training on how to use the tool, and none of the employees in the area was wearing PPE.

    In another situation, two workers were building a wall while remodeling a house. One of the workers was killed when he was struck by a nail fired from a powder-actuated nail gun. The tool operator who fired the nail was trying to attach a piece of plywood to a wooden stud. But
    the nail shot though the plywood and stud, striking the victim.

    Below are some OSHA regulations that should have been followed.
    • Employees using powder- or pressure-actuated tools must be trained to use them safely.
    • Employees who operate powder- or pressure-actuated tools must be trained to avoid firing
      into easily penetrated materials (like plywood).
    • In areas where workers could be exposed to flying nails, appropriate PPE must be used.
    PPE—personal protective equipment (eye protection, hard hat, special clothing, etc.)
    • Low back pain can result from lifting objects the wrong way or carrying heavy loads of wire or other material. Back pain can also occur as a result of injury from poor working surfaces such as wet or slippery floors. Back pain is common, but it can be disabling and can affect young individuals.
    • Chips and particles flying from tools can injure your eyes. Wear eye protection.
    • Falling objects can hit you. Wear a hard hat.
    • Sharp tools and power equipment can cause cuts and other injuries. If you receive a shock, you may react and be hurt by a tool.
    • You can be injured or killed by falling from a ladder or scaffolding. If you receive a shock—even a mild one—you may lose your balance and fall. Even without being shocked, you could fall from a ladder or scaffolding.
    • You expose yourself to hazards when you do not wear PPE.
    All of these situations need to be recognized as hazards.

    Lift with your legs, not your back! You need to be especially careful when working on scaffolding or ladders.

    Summary of Section 5

    You need to be able to recognize that electrical shocks, fires, or falls result from these hazards:
    • Inadequate wiring
    • Exposed electrical parts
    • Overhead powerlines
    • Defective insulation
    • Improper grounding
    • Overloaded circuits
    • Wet conditions
    • Damaged tools and equipment
    • Improper PPE