Motor Control Devices and Circuits: Overview and Objectives

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Learning Goals:

1. Identify pilot devices in a control circuit and their symbols in electrical diagrams.

2. Identify the load circuit and control circuit.

3. Explain the operation of a push-button switch, limit switch, flow switch, level switch, and pres sure switch as they are used as pilot devices.

4. Identify a two-wire control circuit.

5. Identify a three-wire control circuit.

6. Explain the operation of a drum switch as it's used to reverse the operation of an AC or DC motor.

7. Explain the operation of a single-element and a dual-element fuse.

8. Identify the proper enclosure for specific industrial applications.

Introduction

In this section we explain basic motor control circuits commonly in use on the factory floor. It's important to understand that many electronic circuits are used to supplement or replace standard motor control circuits that have been in operation for the last 30 years. These motor control circuits have been named and are easily identified so that when you hear about them on the job or when you see them on the job you will easily recognize them. One must also realize that in the past few years, companies have changed their concept of an electronics technician, and they now expect to hire each person to troubleshoot and repair both the motor control systems as well as the electronic systems. Traditionally troubleshooting the motor control systems has been handled by electricians, and the electronics technician would work on the electronic circuits. In the past several years, companies have streamlined their personnel so that they will either employ an electrician that can work on the electronics or they will hire an electronics technician that can work on motor control circuits. For this reason it's vitally important that you learn as much as you can about standard motor control circuits, so that you can compete for the best-paying jobs.

The circuits in this section are identified so that you will be able to review them when you are on the job. This will be very useful when you find equipment and machinery that incorporates four or five of these basic circuits with additional complex circuits. In these circuits you will be able to gain knowledge that you can transfer to more difficult circuits for troubleshooting and repair. These circuits will include pilot devices and motor starters as well as different types of motors. If you don't understand the function or operation of relays and motor starters, you may need to review the sections on this web site where they were introduced.

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