Reversing Motor Circuits 310

This class describes the proper ways to design reversing motor control circuits for many types of electric motors, using different types of starters and switches.


Class Name:
Reversing Motor Circuits 310
This class describes the proper ways to design reversing motor control circuits for many types of electric motors, using different types of starters and switches.
Number of Lessons:
Additional Language:

Class Outline

  • Objectives
  • What Is a Motor Control Circuit?
  • Motor Starters
  • Why Reverse a Motor Circuit
  • Approaches to Reversing Motors
  • Manual Starters
  • Manual Reversing Starters for DC Motor Circuits
  • Manual Reversing Starters for AC Motor Circuits
  • Magnetic Starters
  • Drum Switches
  • Drum Switches in AC Motors
  • Using Limit Switches
  • Using a PLC
  • Reversing Motor Circuit Safety
  • Summary


  • Define a motor control circuit.
  • Describe motor starters.
  • Explain why motor circuits need reversing.
  • Describe reversing motor circuits.
  • Describe how manual starters are used to reverse circuits.
  • Identify manual reversing DC motor circuits.
  • Identify manual reversing AC motor circuits.
  • Describe magnetic starter reversing motor circuits.
  • Describe drum switches in reversing DC motor circuits.
  • Identify drum switch reversing AC motor circuits.
  • Describe the use of limit switches in reversing motor circuits.
  • Describe PLCs in reversing motor circuits.
  • Describe reversing motor circuit safety.



Vocabulary Term Definition
armature windings The coiled, insulated conductors surrounding the armature through which current is run to create a magnetic field. Reversing the current flow through the armature windings in DC motors reverses motor rotation.
auxiliary contact interlock A backup system used in magnetic motor starters to provide electrical isolation. Also called electrical interlock.
brake To slow and eventually stop motion. Reversing current flow in a motor can be used as a frictionless method of braking.
contactor A device that uses a small control current to energize or de-energize a load. Contactors can handle high amounts of current and are also combined with overload relays to create motor starters.
control circuit A type of circuit that uses control devices to determine when loads are energized or de-energized by controlling current flow. Control circuits usually carry lower voltages than power circuits.
control device Any input device that controls the flow of current in a circuit. Control devices determine when loads are energized or de-energized.
control transformer A electromagnetic device that steps down voltage to levels useable by loads in a control circuit. Control transformers also provide electrical isolation.
drum switch A switch used to manually reverse a motor circuit. A drum switch mounts moving contacts on a rotating shaft.
electrical interlock The type of electrical isolation provided by auxiliary contacts in magnetic motor starters.
field windings The conducting wire connected to the armature that energize the pole pieces. Field windings are connected in series or parallel.
inrush current The initial surge of current into the windings. Inrush current can be up to ten times higher than the continuously needed current because there is low initial resistance.
limit switches A type of switch that detects the presence or absence of an object by physically touching it. Limit switches have a variety of actuators that come into contact with an object.
magnetic starter A magnetic switch with overload protection that uses a solenoid to open and close contacts to a motor circuit.
manual reversing starter A device that combines two manual motor starters to add forward and reverse pushbuttons to the regular start and stop buttons. Reversing starters need only one overload device and must provide mechanical interlock.
manual starter A manual switch with overload protection used to provide control to a motor.
mechanical interlock Arranging forward and reverse contacts so that it is physically impossible for both sets of contacts to close at the same time.
motor control circuit A circuit designed to provide power and control to electric motors.
motor starter An electrically operated switch that uses magnetic induction to provide the startup current for a motor.
NEMA National Electrical Manufacturers Association. NEMA provides ratings for various types of motor designs.
overload relay A relay that is attached to a contactor in order to create a motor starter. Overload relays protect the motor from overload by disconnecting the power to the motor and stopping its operation.
power circuit A type of circuit that carries power to electrical loads. Power circuits often carry high voltages and consist of incoming main power, a motor starter, and the motor.
programmable logic controller A processor driven device that uses logic based software to provide electrical control to machines.
running winding The primary stator winding of a single-phase AC motor. Running windings are constructed from heavy, insulated copper wire.
solenoid principle Using a coil that utilizes voltage to convert electrical energy to mechanical energy via magnetic fields.
starting winding The auxiliary stator winding of a single-phase AC motor. Starting windings are constructed from fine, insulated copper wire.