Introduction to Circuit Protection Devices - a PDH Online Course for Engineers

Introduction to Circuit Protection Devices

Course Outline

Electricity is part of our everyday lives but there are safety hazards associated with the electricity. Safety hazards occur anywhere a person could come into contact with electrical lines or equipment. As long as a person is touching the ground (or something in contact with the ground), electricity has the potential to travel through him or her, causing shock, burn, or even death. Fuses and circuit breakers are protective devices used to ensure that too much current does not flow through a circuit. A fuse or circuit breaker is designed to create an open circuit if too much current flows through it. You can think of it as a switch that automatically turns itself off if the current through it exceeds a certain level.

This course provides you with insight to how circuit protection devices work.

This 4-hr course material is based entirely on Naval Education and Training Materials (NAVEDTRA 14175), Electricity and Electronic Training Series; Module-3 “Circuit Protection Devices” and covers Chapter 2.

The course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of course materials.

Learning Objective

At the conclusion of this course, the student will be able to:

State the reasons why circuit protection is needed;
State the three conditions i.e. direct short, excessive current and excessive heat that require circuit protection;
State the way the circuit protection devices are connected in a circuit;
Identify two types of circuit protection devices and label the schematic symbols for each type;
State the difference between fuse and circuit breakers;
List the three categories of time delay ratings for fuses and state a use for each type of time-delay rated fuse;
List the methods of checking for an open fuse;
Select a proper replacement and substitute fuse from a listing of fuses;
Describe three types of circuit breaker trip elements and how each type of trip element reacts to excessive current;
Define the circuit breaker terms trip-free and non trip-free and list the uses of each of these types;
Understand what is selective tripping and state why it is used; and
Identify the factors used in selecting circuit breakers and list the steps to follow before starting work on a circuit breaker.

Intended Audience

This course is aimed at students, professional electrical & electronics engineers, service technicians, energy auditors, operational & maintenance personnel, facility engineers and general audience.

Course Introduction

You must have wondered that why the birds sitting on an electric line don't get shocked?

This is because they aren't touching anything that is touching the ground. The lines they sit on are insulated from the ground by glass or ceramic disks. The disks don't allow the lines to touch the poles which would be a route to the ground. However, if those birds take flight and their wings touch two lines at once, or if they touch a pole and wire at the same time, they will get shocked and could die.

The technical explanation to this fact is that electricity always travels the easiest path to ground. It is this attribute of electricity that makes it dangerous to people, because we are almost always touching the ground or something in contact with the ground.

Safety devices including 3-pronged plugs, Ground Fault Circuit Interrupters, fuses, and circuit breakers are built into circuits to help prevent dangerous situations.
Switches are a convenient way to open and close a circuit. Circuit breakers and fuses are like automatic switches that open a circuit if it becomes overloaded.

Course Content

In this course, you are required to study Naval Education and Training Materials (NAVEDTRA 14175), Electricity and Electronic Training Series; Module-3, Chapter 2 titled “Circuit Protection Devices”:

Circuit Protection Devices (Chapter 2, NAVEDTRA 14175)

Please click on the above underlined hypertexts to view, download or print the documents for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader.

Course Summary

Electricity only travels in a closed loop called a circuit and the circuits can carry a specific amount of electricity. That amount is measured in watts, volts, and amps. When there is some kind of "leak" in a circuit, the electricity flows out of its specified path.

In a circuit, as more resistors are added in parallel, the total resistance decreases, which causes an increase in the total amount of voltage. Circuit protection devices are protective items used to ensure that too much current does not flow through a circuit. Two common type of circuit protection devices are fuses and circuit breakers.

Fuse is a piece of conductor that breaks/melts, if too much current goes through it; it is not reusable.
Circuit breaker is a switch that flips, if too much current goes through it; it is reusable.

If the circuit breaker didn't trip or the fuse didn't blow, this could cause a fire. It is important that these elements are properly sized and selected to suit the application. Remember, electricity will always take the easiest path to the ground.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.