Motor Control Circuits and Functions
A small motor can be started by simply plugging it into an electrical receptacle or by using a switch or circuit breaker. A large motor requires a specialized switching unit called a motor starter or motor contactor. Once they are running, there are many other aspects to safe and efficient motor operation. Motor control refers to manual or automatic methods for starting, stopping, controlling speed, reversing, and protecting a motor. These controls are achieved using a variety of circuits, connections and sensors.
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Learning Objectives
• Explain how circuits help control starting, stopping, reversing, speed control, motor protection, and safety • Identify and describe common circuit types (start/stop, jogging, interlocking, multiple station, and sequencing) • Differentiate between 2 and 3 wire start/stop circuits • Differentiate between Permissive and Restrictive interlocks
Specs
| Course Level | Intermediate |
| Languages | English, Portuguese, Polish, Russian |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
What are motor controls?
Manual or automatic methods for starting, stopping, controlling speed, reversing, and protecting a motor.
What is a 2-wire control circuit?
A circuit with a single switch in series with the motor and the starter or relay that provides power to the motor.
What is an interlock?
A method of preventing certain events or conditions from occurring in electrical or mechanical devices; an example is a two-hand control.
How can the speed of an AC motor be controlled?
One common way is by using a variable frequency drive (VFD) with a potentiometer.
What is a motor protection device?
A device that will stop a motor in the event of a problem. Examples include thermal overload switches, overspeed switches, over- or under-voltage detectors, vibration monitors, and other devices designed to prevent damage to the motor itself.
Sample Video Transcript
The three-wire control has a start device, stop device, and an electrical interlock. After the start device is initiated, it will energize the coil of the relay or starter. This will close a contact that is wired in parallel with the start device. This closed contact will allow the start device to be released and returned to its normally open state. The contact will maintain continuity in the circuit and hold in the coil of the relay. The stop device will open the circuit and remove voltage to the coil. This will, in turn, open the contact around the start device and not allow the circuit to restart when the stop device is returned to its normally closed state.
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