What is a Contactor? | Working Principles | Summary and Q&A

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July 26, 2021
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RealPars
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What is a Contactor? | Working Principles

TL;DR

This video explains the purpose of contactors, how they function, and the differences between contactors and relays.

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Questions & Answers

Q: How does a contactor protect a PLC from damage?

A contactor protects a PLC by acting as an intermediary between the PLC and the high voltage motor, preventing electrical surges from damaging the PLC cards.

Q: Can a relay be used instead of a contactor to control a high voltage motor?

No, relays are typically used for smaller devices with lower current and voltage ratings, while contactors are designed to handle the higher currents and voltages required for larger devices.

Q: How can you determine the voltage requirement for a contactor's coil?

Before connecting the wires to the coil, it is necessary to check the coil voltage specified by the contactor. Most contactors, like the one shown in the video, work with a 24 volt DC power supply.

Q: What is the purpose of the auxiliary or feedback contact on a contactor?

The auxiliary or feedback contact on a contactor is used to send a signal to the PLC input to monitor the health of the contactor. It provides a way to detect if the contactor is broken.

Q: How do you wire a contactor to control a motor using a PLC?

To control a motor using a PLC through a contactor, you need to connect the PLC output to the coil of the contactor, and then connect the three-phase power supply to the L1, L2, and L3 terminals. From the other end, you connect the T1, T2, and T3 terminals to the motor. Additionally, an auxiliary or feedback contact should be connected to the PLC input to monitor the contactor's health, and a start/stop switch should be connected to the PLC input for control.

Summary & Key Takeaways

  • A contactor is a device used to make and break electrical power circuits, often used to control high voltage motors.

  • Contactors work by using a low voltage coil that, when energized, creates an electromagnetic field that closes the contacts and allows power to reach the motor.

  • Contactors differ from relays in that they are designed to handle higher currents and voltages, making them suitable for larger devices.

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