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  MODULE 1: ELECTRICITY IS DANGEROUS


Introduction

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!

Terms you need to know

What is "voltage"? Voltage 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 "amperage"? Amperage 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 will of water 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 "resistance"? Resistance is the unit(ohms)used to measure the opposition to the flow of electrical current. This is pretty easy to understand. A small waster pipe is going to oppose a lot of water from flowing. Only a 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 is a "circuit"? A circuit is the a complete path for the flow of current. Electrical current may flow through a circuit through a series or parallel path.
  • 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.

How do you receive an electrical shock?

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, or what electrical workers call "complete the circuit," if you touch both of them at the same time. 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 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.

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.

Don't know what a word means? See the Glossary.

Take the review Quiz Most (but not all) questions on the final exam are derived from module quizzes.

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This material is for training purposes only to inform the reader of occupational safety and health best practices and general compliance requirements and is not a substitute for provisions of the OSH Act of 1970 or any governmental regulatory agency. Copyright © 2000-2008 Geigle Communications, LLC. All rights reserved. Federal copyright law prohibits unauthorized reproduction by any means and imposes fines up to $25,000 for violations. Students may reproduce materials for personal study.