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

Electricity Is Dangerous

Whenever you work with power tools or on electrical circuits there is a risk of electrical hazards, especially electrical shock. Anyone can be exposed to these hazards at home or at work. Workers are exposed to more hazards because job sites can be cluttered with tools and materials, fast-paced, and open to the weather. Risk is also higher at work because many jobs involve electric power tools.

Electrical trades workers must pay special attention to electrical hazards because they work on electrical circuits. Coming in contact with an electrical voltage can cause current to flow through the body, resulting in electrical shock and burns. Serious injury or even death may occur. As a source of energy, electricity is used without much thought about the hazards it can cause. Because electricity is a familiar part of our lives, it often is not treated with enough caution. As a result, an average of one worker is electrocuted on the job every day of every year! Electrocution is the third leading cause of work-related deaths among 16- and 17-year-olds, after motor vehicle deaths and workplace homicide. Electrocution is the cause of 12% of all workplace deaths among young workers.1

Note to the learner—This manual describes the hazards of electrical work and basic approaches to working safely. You will learn skills to help you recognize, evaluate, and control electrical hazards. This information will prepare you for addi-tional safety training such as hands-on exercises and more detailed reviews of regulations for electrical work. Your employer, co-workers, and community will depend on your expertise. Start your career off right by learning safe practices and developing good safety habits. Safety is a very important part of any job. Do it right from the start.
  • Electrical shock causes injury or death!

Electrical work can be deadly if not done safely.

This manual will present many topics. There are four main types of electrical injuries: electrocution (death due to electrical shock), electrical shock, burns, and falls. The dangers of electricity, electrical shock, and the resulting injuries will be discussed. The various electrical hazards will be described. You will learn about the Safety Model, an important tool for recognizing, evaluating, and controlling hazards. Important definitions and notes are shown in the margins. Practices that will help keep you safe and free of injury are emphasized. To give you an idea of the hazards caused by electricity, case studies about real-life deaths will be described.

How Is an Electrical Shock Received?

An electrical shock is received when electrical current passes through the body. Current will pass through the body in a variety of situations. Whenever two wires are at different voltages, current will pass between them if they are connected. Your body can connect the wires if you touch both of them at the same time. Current will pass through your body.

Wires Carry Current

In most household wiring, the black wires and the red wires are at 120 volts. The white wires are at 0 volts because they are connected to ground. The connection to ground is often through a conducting ground rod driven into the earth. The connection can also be made through a buried metal water pipe. If you come in contact with an energized black wire—and you are also in contact with the neutral white wire—current will pass through your body. You will receive an electrical shock.

  • current - the movement of electrical charge
  • voltage - a measure of electrical force
  • circuit - a complete path for the flow of current
  • You will receive a shock if you touch two wires at different voltages at the same time.
  • ground - a physical electrical connection to the earth
  • energized (live, “hot”) - similar terms meaning that a voltage is present that can cause a current, so there is a possibility of getting shocked
  • conductor - material in which an electrical current moves easily
  • neutral - at ground potential (0 volts) because of a connection to ground
  • You will receive a shock if you touch a live wire and are grounded at the same time.
  • When a circuit, electrical component, or equipment is energized, a potential shock hazard is present.

  • Black and red wires are usuallyenergized, and white wires are usually neutral.

    Metal electrical boxes should be grounded to prevent shocks.

    If you are in contact with a live wire or any live component of an energized electrical device—and also in contact with any grounded object—you will receive a shock. Plumbing is often grounded. Metal electrical boxes and conduit are grounded.

    Your risk of receiving a shock is greater if you stand in a puddle of water. But you don't even have to be standing in water to be at risk. Wet clothing, high humidity, and perspiration also increase your chances of being electrocuted. Of course, there is always a chance of electrocution, even in dry conditions.

    You can even receive a shock when you are not in contact with an electrical ground. Contact with both live wires of a 240-volt cable will deliver a shock. (This type of shock can occur because one live wire may be at +120 volts while the other is at -120 volts during an alternating current cycle—a difference of 240 volts.). You can also receive a shock from electrical components that are not grounded properly. Even contact with another person who is receiving an electrical shock may cause you to be shocked.

    A 30-year-old male electrical technician was helping a company service representative test the voltage-regulating unit on a new rolling mill. While the electrical technician went to get the equipment service manual, the service representative opened the panel cover of the voltage regulator’s control cabinet in preparation to trace the low-voltage wiring in question (the wiring was not color-coded). The service representative climbed onto a nearby cabinet in order to view the wires. The technician returned and began working inside the control cabinet, near exposed energized electrical conductors. The technician tugged at the low-voltage wires while the service representative tried to identify them from above. Suddenly, the representative heard the victim making a gurgling sound and looked down to see the victim shaking as though he were being shocked. Cardiopulmonary resuscitation (CPR) was administered to the victim about 10 minutes later. He was pronounced dead almost 2 hours later as a result of his contact with an energized electrical conductor.

    To prevent an incident like this, employers should take the following steps:

    • Establish proper rules and procedures on how to access electrical control cabinets without getting hurt.
    • Make sure all employees know the importance of de-energizing (shutting off) electrical systems before performing repairs.
    • Equip voltage-regulating equipment with color-coded wiring.
    • Train workers in CPR.

    A maintenance man rode 12 feet above the floor on a motorized lift to work on a 277-volt light fixture. He did not turn off the power supply to the lights. He removed the line fuse from the black wire, which he thought was the “hot” wire. But, because of a mistake in installation, it turned out that the white wire was the “hot” wire, not the black one. The black wire was neutral. He began to strip the white wire using a wire stripper in his right hand. Electricity passed from the “hot” white wire to the stripper, then into his hand and through his body, and then to ground through his left index finger. A co-worker heard a
    noise and saw the victim lying face-up on the lift. She immediately summoned another worker, who lowered the platform. CPR was performed, but the maintenance man could not be saved. He was pronounced dead at the scene.

    You can prevent injuries and deaths by remembering the following points:

    • If you work on an electrical circuit, test to make sure that the circuit is de-energized (shut off)!
    • Never attempt to handle any wires or conductors until you are absolutely positive that their electrical supply has been shut off.
    • Be sure to lock out and tag out circuits so they cannot be re-energized.
    • Always assume a conductor is dangerous.

     Always test a circuit to make sure it is de-energized before working on it.

    Summary of Section 1

    You will receive an electrical shock if a part of your body completes
    an electrical circuit by

    • touching a live wire and an electrical ground, or
    • touching a live wire and another wire at a different voltage.