Electrical Distribution Systems MOTOR CONTROLLERSMOTOR CONTROLLERSMotor controllers range from a simple toggle switch to a complex system usingsolenoids, relays, and timers. The basic functions of a motor controller are tocontrol and protect the operation of a motor.EO 1.6 STATE the function of motor controllers.EO 1.7 STATE three protective features (overloads) that maybe incorporated into a motor controller.EO 1.8 Given a simplified drawing of a motor controller,DESCRIBE the operation of that motor controller.MotorControllersMotor controllers range from a simple toggle switch to a complex system using solenoids, relays,and timers. The basic functions of a motor controller are to control and protect the operation ofa motor. This includes starting and stopping the motor, and protecting the motor fromovercurrent, undervoltage, and overheating conditions that would cause damage to the motor.There are two basic categories of motor controllers: the manual controller and the magneticcontroller.ManualControllersA manual controller, illustrated by Figure 9, is a controller whose contact assembly is operatedby mechanical linkage from a toggle-type handle or a pushbutton arrangement. The controlleris operated by hand.The manual controller is provided with thermal and direct-acting overload units to protect themotor from overload conditions. The manual controller is basically an "ON-OFF" switch withoverload protection.Manual controllers are normally used on small loads such as machine tools, fans, blowers,pumps, and compressors. These types of controllers are simple, and they provide quiet operation.The contacts are closed simply by moving the handle to the "ON" position or pushing theSTART button. They will remain closed until the handle is moved to the "OFF" position or theSTOP button is pushed. The contacts will also open if the thermal overload trips.Manual controllers do NOT provide low voltage protection or low voltage release. When powerfails, the manual controller contacts remain closed, and the motor will restart when power isrestored. This feature is highly desirable for small loads because operator action is not neededto restart the small loads in a facility; however, it is undesirable for larger loads because it couldcause a hazard to equipment and personnel.Rev. 0 Page 15 ES-15
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