Components for Electric Motors: Objectives and Introduction

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  • • Identify and explain the operation of motor starting relays and other starting components that are used on single-phase hermetic compressor motors.
  • • Select the correct potential relay for an application with information available on the potential relay to be replaced.
  • • Troubleshoot and install motor starting relays on hermetic compressor motors.
  • • Lubricate and identify the types of bearings used in electric motors.
  • • Identify the type of motor drives used on industry applications.
  • • Calculate the variables in a V-belt drive application to obtain the desired equipment rpm.
  • • Recognize and adjust a V-belt application to the proper tension and alignment.


  • Back electromotive force
  • Ball bearings
  • Bearing
  • Current or magnetic relay
  • Direct drive
  • Full-load amperage
  • Locked rotor amperage
  • Potential relay
  • Sleeve bearings
  • Solid-state relay
  • Starting relay
  • V-belt


In Section 9 we discussed electric motors and some, of their starting components. In this section we discuss the starting components used on single- phase hermetic motors. Single-phase hermetic motors and other special motors require some type of external starting component because they are enclosed in a sealed case. Three types of starting relays are used on this type of motor: current, potential, and solid state. These devices are used on most single-phase hermetic compressor motors with the exception of permanent split-capacitor motors.

Electric motors must have bearings to permit smooth and easy rotation. The ball bearing or the sleeve bearing is used in most motors. Motors also must have some means of transferring their rotating motion to the device being powered by the motor. A direct-drive hookup transfers the rotating motion directly from the motor to the device. The belt-drive hookup transfers the rotating motion to the device by a belt connection.

Magnetic starters and push buttons are used to stop and start electric motors. A magnetic starter opens and closes sets of contacts to stop and start loads. The magnetic starter also incorporates overload protection for the device it controls. Push-button switches are used to control magnetic starters in most cases.

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