Motor Starters

SKU: C-588Duration: 12 Minutes

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Language:  English

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Course Details


Training Time: 12 minutes

Compatibility: Desktop, Tablet, Phone

Based on: Industry Standards and Best Practices

Languages: English

A motor starter consists of a contactor and an overload protection device. A contactor is a switch with contacts designed for high voltages and currents. Electromagnetic contactors allow remote control of motors using a low voltage control circuit. A motor starter also incorporates an overload protection device. This is a thermal safety feature that will prevent overheating and motor damage caused by operating for a prolonged period of time at a current that is moderately above its full load amperage. This module covers all the components of a motor control system, with an emphasis on the function and operation of the motor starter components.

Learning Objectives

  • Describe the major components that make up a motor starter
  • Explain how an electromagnetic contactor operates
  • Explain the purpose of an overload protection device
  • Explain the operation of an overload protection device
  • Explain the difference between an overload protection device and a circuit breaker
  • Explain how a heater element can be used for troubleshooting
  • Describe some of the additional functionalities that can be added to motor starters
  • Describe the advantages of a solid-state motor starter

Key Questions

The following key questions are answered in this module:

What is a contactor?
A contactor is a multi-contact switch, often activated electromagnetically, designed to start and stop large electric currents at high voltages.

What is the difference between circuit breakers and overload protection devices?
Circuit breakers operate by stopping power in very high overcurrent situations such as those that would occur from a short circuit or a ground fault. An overload protection device is meant to protect a motor from operating for prolonged periods of time at a current that is moderately above full load amperage.

How does a bimetallic overload protection device work?
Bimetallic strips bend when heated. In an overload device, a small heater is wired in series with a motor winding. If excessive current flows through the heater, it causes the strip to bend sufficiently to open the contacts that supply power to the motor winding.

What are some types of alternative starters that are available?
A typical starter is an electromechanical starter which connects all motor windings simultaneously. This is called an across-the-line starter. More complex starter systems allow for reversal of the motor, multi-speed starts and reduced voltage starts.

What are the advantages of a solid-state starter over an electromagnetic starter?
Solid-state starters offer faster switching, the elimination of mechanical contacts and pitting, and the ability to more precisely control the voltage applied during startup.

Sample Video Transcript

Below is a transcript of the video sample provided for this module:

Note that there are two electrical circuits in a contactor, one is the control circuit connected to the coil that typically runs at a lower voltage, such as 24 or 120 volts. The second circuit is the primary power circuit that connects the power lines to the motor through the contactor contacts. As mentioned earlier, the contactor closes or opens all three power lines simultaneously when the coil moves the core. The contactor also simultaneously activates auxiliary contacts which can be used for control purposes and for contactor status reporting.

Additional Resources

Use the additional resources and links below to learn more about this topic:

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