What You Need to Know About the Motor Control Circuit

This video contains a complete explanation of the circuit and how it operates:

Lecture Notes

The Motor Starter

Here is a Motor Starter with all of the parts labeled:

The Typical Motor Control Circuit

Power Circuit:
The power circuit uses:

- L1, L2, and L3
  - incoming power that the motor uses to run
- T1, T2, and T3
  - outgoing power
  - where the motor is connected
- overload relay
  - acts as a fuse to protect the motor

Motor Control Circuit:

The motor control circuit (which is the focus of this course) uses:

- the coil
- the auxiliary contacts
- the overload contacts

The coil, when energized by the motor control circuit, closes the contacts that connect L1, L2, and L3 (incoming power) to T1, T2, and T3 (outgoing power), which is what sends power to a motor. Incoming three phase power is connected to L1, L2, and L3, and the motor is connected to T1, T2, and T3.

The overload contacts monitor the state of the overload relay, which acts like a fuse. If the motor that is connected to T1, T2, and T3 draws too much current, the overload relay "trips", which means that it disconnects the power to the motor. The overload contact monitors the state of the overload relay. There is a normally open set of overload contacts and a normally closed set of overload contacts.

The auxiliary contacts monitor the state of the contacts that connect L1, L2, and L3 to T1, T2, and T3. When the coil is energized, those contacts close and the auxiliary contacts close as well. There is a normally open set of auxiliary contacts and a normally open set.

Here is a typical motor control circuit, which uses the control components of the motor starter:

You will build one just like this in Lab 3-2.

It is attributed to: Rockis, Gary J. and Mazur, Glen A. (2009). Chapters 4 & 9. Electrical Motor Controls for Integrated Systems, 4th Edition.

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