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Course 715 - Electrical Safety for Technicians & Supervisors

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

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 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!

Real-Life Example

A 29-year-old male welder was assigned to work on an outdoor concrete platform attached to the main factory building. He wheeled a portable arc welder onto the platform. Since there was not an electrical outlet nearby, he used and extension cord to plug in the welder. The male end of the cord had four prongs and the female end was spring-loaded. The worker plugged the male end of the cord into the outlet. He then plugged the portable welder’s cord into the female end of the extension cord. At that instant, the metal case around the power cord plug became energized, electrocuting the worker.

An investigation showed that the female end of the extension cord was broken. The spring, cover plate, and part of the casing were missing from the face of the female connector. Also, the grounding prong on the welder’s power cord plug was so severely bent that it slipped outside of the connection. Therefore, the arc welder was not grounded. Normally, it would have been impossible to insert the plug incorrectly. But, since the cord’s female end was damaged, the “bad" connection was able to occur.

To prevent this from happening to you or one of your co-workers, use these safe practices:

  • Thoroughly inspect all electrical equipment before beginning work.
  • Do not use extension cords as a substitute for fixed wiring. In this case, a weatherproof receptacle should have been installed on the platform.
  • Use connectors that are designed to stand up to the abuse of the job. Connectors designed for light-duty use should not be used in an industrial environment.

Terms You Need to Know

What is a "volt"? A Volt is a measure of the electrical force that seems to push the current along. Think of voltage as a lot of water stored in a high water tank. Because the water tank is high, the water will have more force behind it as it flows down the water pipe to your home. This is why they put water tanks up high! :-) If the same tank was placed at ground level, your water pressure would not be as great. By the way, the symbol for voltage is "V".

What is an "ampere"? An ampere is the unit used to measure the amount of electrical current. Amperage is often referred to as "current" by electrical workers and engineers. Let's go back to our water tank. If diameter of your pipe coming from the water tank is large, a lot of water (amperage) will flow through the pipe. If the pipe's diameter is small, a smaller amount of water will flow through the pipe. If you need a lot of current (many amps) to operate your equipment, you'll need large wires to run the current or they'll burn up! The symbol for amperage is "I".


What is an "ohm"? Think of an ohm as "resistance". An ohm is the unit used to measure the opposition (a.k.a. resistance) to the flow of electrical current. This is pretty easy to understand. A small water pipe is going to oppose a lot of water from flowing. Relatively little water will be able to flow through the pipe. So, the pipe offers a high resistance to the flow of water. You can see that a large pipe would offer little resistance to the flow of water. Big pipe: a lot of water! It's that simple. In an electrical circuit, components are usually sources of resistance. Any component that heats up due to electrical current is a source of resistance. The symbol for resistance is "R".

  • What's a "series" circuit? The current in a series circuit takes only one path. For example, water from high in the mountains may flow down one stream (series)into a river that flows to the ocean.
  • What's a "parallel" circuit? The current in a parallel circuit takes many paths. For example, the water flowing from a water tank up on a hill will flow through many different water pipes (parallel) before it reaches the ocean.

Real-Life Example

A female assistant manager of a swim club was instructed to add a certain chemical to the pool. She went down into the pump room, barefoot. The room was below ground level, and the floor was covered with water. She filled a plastic drum with 35-40 gallons of water, then plugged a mixing motor into a 120-volt wall outlet and turned on the motor. The motor would be used to mix the water and the chemical, then the solution would be added to the pool. While adding the chemical to the water in the drum, she contacted the mixing motor with her left hand. Apparently, the motor had developed a ground fault. Because of the ground fault, the motor was energized and she was electrocuted. A co-worker found the victim slumped over the drum with her face submerged in water. The co-worker tried to move the victim but was shocked. The assistant manager was dead on arrival at a local hospital.

An investigation showed that the mixing motor was in poor condition. The grounding pin had been removed from the male end of the power cord, resulting in a faulty ground. The circuit was equipped with a GFCI, but it was not installed properly. A properly wired and functioning GFCI could have sensed the ground fault in the motor and de-energized the circuit.

Take a look at what could have been done to prevent this death:

  • The employer should have kept the motor in better condition. Power cords should be inspected regularly, and any missing ground prongs should be replaced.
  • All pool-area electrical circuits should be installed by qualified electricians.
  • The victim should have worn insulating boots or shoes since she was handling electrical equipment.
  • The employer should have followed the law. The NEC requires that all pool-associated motors have a permanent grounding system. In this case, this regulation was not followed. Also, electrical equipment is not permitted in areas without proper drainage.
  • OSHA requires employers to provide a work environment free of safety and health hazards.

Electrical Shock Causes

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. This is what electrical workers call "complete the circuit". Therefore, current will pass through your body.

In most household wiring in the U.S., 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 the ground is often through conducting ground rods driven into the earth.

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.

Black and Red wires are usually energized, and white wires are usually neutral metal electric boxes should be grounded to prevent shocks
always test circuits
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.

Real-Life Example

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 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.


Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. ___________ is a measure of the electrical force that seems to push the current along.

2. _______ is the unit used to measure the amount of electrical current.

3. _______ is the unit(ohms)used to measure the opposition to the flow of electrical current.

4. Whenever two wires are at different _________, current will pass between them if they are connected.

5. You can receive an electrical shock when you are not in contact with an electrical ground.

Have a great day!

Important! You will receive an "error" message unless all questions are answered.