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Hey, in this article we are going to see proper electrical contactor connection and wiring diagram for normal operation, star-delta starter, motor control, light control, etc. Also, we will discuss the internal circuit diagram of the contactor used for power control.
In simple words, Electrical Contactor is an electrically operated switch whose main function is to connect or disconnect the load from the power source. Basically, the contactor work as a medium when we control a high voltage, high current power circuit by a low voltage, low current control circuit.
Before you going to do a connection for a contactor you must know about its terminals and contacts. Basically, a contactor has two types of contacts – 1. Main or Power Contacts and 2. Auxiliary Contacts
In the below figure, you can see there is a total of 16 terminals in the contactor.
A1 and A2 are magnetic coil terminals.
L1, L2, and L3 are the incoming terminals of the main contact which are to be connected to the main power supply.
T1, T2, and T3 are the outgoing terminals of the main contact which are to be connected to the load.
Here two NC and two NO auxiliary contacts are available. Each of them has two terminals.
1. Generally the magnetic coil of a contactor is designed to operate at a low voltage such as 230V AC, 110V AC, 24V DC, etc. So provide the power supply to the magnetic coil as per requirement.
2. Connect the main power supply terminal with the incoming terminals of the contactor.
3. Connect the load with the outgoing terminals of the contactor.
Now we are going to see, how to connect the push button switch with a contactor. Here the connection diagram in the below figure.
You can see here, two push button switches are used. NC push button(green colour) switch is used to turn off the contactor whereas the NO push button(Red colour) switch is used to turn on the contactor.
These pushbutton switches break or make the contacts only when we press the button. Once we release the button its contacts also come back to their old position. So the magnetic coil of the contactor is also connected through the NO auxiliary contacts. So the contactor will be turned on once we press the switch and remain On even when we release the NO push button. The contactor will remain turned on until we press the NC push button.
Now, let’s go to know how to connect indication lamps with a contactor to give indications whether it is in ON condition or OFF condition. See the below diagram.
Here we have taken two indication lamps – Red for ON, Green for OFF.
You can see the Red indication lamp is connected through the NO auxiliary contact. So when the contactor turning on it will glow. On the other hand, the green indication lamp is connected through the NC auxiliary contact. So when the contactor is in OFF condition, this lamp will glow. Once the contactor is turned ON it will off and the red colour lamp will glow.
Thermal Overload Relay is mainly used to give protection against overload fault. So thermal overload relay used with electrical contactor when we designed DOL Starter, Star Delta Starter, etc.
Here you can see the connection of thermal overload relay with a contactor in the DOL Starter Circuit.