Motor Control Basics: Starters, Contactors, and Control Circuits
Industrial motors are switched by control circuits, not by flipping a big switch. Understanding contactors, overloads, and the control logic is core to industrial and maintenance electrical work.
QUICK ANSWER
A motor starter combines a contactor, which switches motor power, with an overload relay that protects the motor from excessive current. A low-voltage control circuit with start and stop pushbuttons energizes the contactor coil, and a holding contact keeps the motor running after the start button is released. This separation of power and control circuits is the foundation of motor control.
Power vs Control
Motor control separates the high-current power circuit from a low-voltage control circuit. The contactor coil, energized by the control circuit, pulls in the main contacts that feed the motor. The overload relay watches motor current and drops the circuit if it runs too high for too long, protecting the windings.
Start-Stop and Holding Contacts
- Start button: momentarily energizes the contactor coil.
- Holding contact: keeps the coil energized after start is released.
- Stop button: breaks the control circuit and drops the motor.
- Overload: trips on sustained overcurrent.
The seal-in is the trick
The holding, or seal-in, contact is what confuses newcomers. It is how a momentary button press keeps a motor running until stop is pressed.
Motor control leads into variable frequency drives and motor testing.
WE BUILD THIS IN VR — THE PRIME VR
We build motor control into VR, so learners wire a start-stop station, trace the seal-in circuit, and troubleshoot a starter while the system models coil, contact, and overload behavior. Practicing the control logic in immersion makes the seal-in and troubleshooting intuitive.
Book a discovery callFrequently Asked Questions
What is the difference between a contactor and a motor starter? +
A contactor is an electrically controlled switch for the motor power circuit, while a motor starter adds an overload relay for motor protection. A starter is a contactor plus overload protection.
What is a holding or seal-in contact? +
A holding contact is an auxiliary contact on the contactor that keeps the coil energized after the momentary start button is released, so the motor keeps running until the stop button breaks the circuit.
What does an overload relay do? +
An overload relay monitors motor current and opens the control circuit if current stays too high for too long, protecting the motor windings from overheating and damage.
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Train motor control in VR
We build starter and control circuits into immersive, scored practice.