magnetic contactor
A part of a control device for a motor. When the control switch is closed, the contactor, which consists of a coil and a pivot arm, closes the contact. This completes the motorís power circuit.

microprocessor
A computerís central arithmetic and logic unit and control unit on a single integrated circuit chip.

motor overload
A thermal mechanical switch in the line to the motor which provides protection to the motor from overload. When an overload condition exists, the overload will open its control contact. This then either opens the motor starterís contactor or stops the associated adjustable frequency drive. Adjustable frequency drives for single motor applications either require a thermal mechanical motor overload or provide electronic circuitry which takes the place of the motor overload. For multi-motor applications, thermal mechanical motor overloads must be supplied and properly sized for each motor.

motor starter
The simplest kind of a motor starter is an across-the-line motor starter consisting of a motor overload and a contactor that the motor overload can open and so remove power from the motor in case of an overload. A properly sized motor overload provides overload protection for the motor. Special types of motor starters may also reduce the current inrush to the motor. See reduced voltage starter and part winding starter. An adjustable frequency drive eliminates the need for a motor starter unless a bypass circuit is included. Then a motor starter is needed in the bypass circuit. An adjustable frequency drive should not drive a motor through any reduced voltage or part winding starter, and it should not be connected to the output of either of these.