Overload Relay Connection Diagram and Wiring


In this article, we are going to see Overload Relay Connection Diagram and Wiring. An Overload relay is an electrical protective device that gives protection to electrical machines, devices, or equipment against overload current fault. Here, we will see the connection of overload relay that operates with three-phase. This is the Thermal overload relay, and it mainly used with an electrical contactor in motor control circuits or motor starter circuits(DOL starter, Star Delta Starter).


Overload Relay Terminals Diagram


Here, you can see a diagram of the three-phase thermal overload relay is given below.

overload relay diagram, overload relay terminals


The overload relay(OLR) has a total of six main power terminals. The upper three metallic rod terminals are the input terminals. And the bottom, T1, T2, T3 are to be connected with the load. 
Here, you can also see the overload relay has one NC contact and one NO contact. Each of them having two terminals. NO, NC contacts are capable to handle low voltage(generally 230V), and Low Current.

In normal condition, when a rated current flowing through the Main contacts, the NC contacts will be closed condition and NO contacts will be in the open condition. Once the overload relay tripped due to the excess current flowing through it, its NC contacts become open and NO contacts become close.

You can also see, the overload relay has STOP and RESET switch. So we can manually stop or disconnect the main power supply by pressing the STOP switch. And the RESET switch gives the function to RESET the overload relay once it got tripped. The overload relay also has a current adjusting knob, using that we can set the current. So when the current above that set current will flow it will be trip.




Connection of Overload Relay with Contactor


Generally, in most cases, the thermal overload relay used with an electrical contactor. The overload relay operates the contactor to get turned when an overload fault occurs. Here you can see the diagram to connect a three-phase thermal overload relay with a three-phase contactor.

connection of overload relay with contactor


Insert the metallic rod terminals of the overload relay to the bottom side of the contactor as shown in the above figure, then tighten the screws. Now the overload relay properly connected with the contactor.




Overload Relay Wiring Connection


Now we are going to see the electrical connection for the overload relay and contactor. Here the connection diagram is given below.

overload relay connection diagram, overload relay wiring diagram


Here, you can see in the above diagram the Coil of the contactor(A1 terminal) is connected through the NC contact of the overload relay. So when the overload relay got tripped, its NC contact becomes open so the coil of the contactor will be disconnected from the power supply, hence the contactor will be turned off and disconnect the main power supply to the load.




How to Do Overload Relay Connection


1. First, select the overload relay with a proper rating which will suitable for your load as well as with the contactor.

2. Connect the overload relay with the contactor as shown in the above figure.

3. Connect the one NC terminal of the relay with anyone phase through the NC push button switch as shown in the figure.

4. Connect another NC terminal of the relay with the A1 terminal of the contactor through the NO push button switch as shown in the figure.

5. Connect the yellow colour pilot lamp with the NO contacts of the relay as shown in the figure, it will glow once the relay got tripped.

6. Connect the A2 terminal of the contactor with the neutral wire.

7. Connect the A1 terminal of the contactor with the incoming of NO push-button switch through the NO contacts of that contactor that makes the holding circuit for the contactor.

8. Finally, review your circuit with the above connection diagram, is all connections are done properly.


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Overload Relay Connection Diagram and Wiring Overload Relay Connection Diagram and Wiring Reviewed by Author on 5/09/2021 Rating: 5
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