In this post, we are going to learn How to Test a Relay with a Multimeter, Step by Step

# How to Test a Relay with a Multimeter?

The main reason for testing a relay is to find, whether it is a good or defective one. The simplest way of finding this is to use a multimeter with an ohmmeter setting and then measuring the resistance values by checking its terminals. In this article, we will see what resistance readings are required to declare that the relay you are using is the good or defective one.

Relay

To do this there are only two easy steps to follow:

• Step.01: Check the relay coil Terminals using Multimeter.
• Step.02: Test the Relay contacts using Multimeter.

## Step.01:

Check the Relay’s Coil Terminals Using a Multimeter:
To check the relay whether it’s good or faulty one, we need to check the resistance of a coil. In the Relay, there is a coil and that coil has some resistance, using that resistance knowledge we can find that the relay is a good one or not.

This is how we can do this:

First of all take the relay and search that particular relay on the internet you will find the datasheet of that particular relay. Now in that datasheet, you will find the coil resistance and tolerance value. Note that values and move on the second step, which is finding the resistance value of a coil with a multimeter.

Let’s say A relay has a coil resistance of 400Ω then when you measure the actual relay’s coil terminals with a multimeter you should get the values in between of 350Ω to 450Ω.  Otherwise your relay is faulty and in this case, you have to replace it.

Example of Datasheet of Relay

#### The procedure of Checking the Coil’s Resistance of a relay with a Multimeter:

To check the coil’s resistance with a multimeter, take a multimeter and put it on the ohmmeter setting then connect the multimeter probes on any two terminals of relay’s coil. You will find the resistance of the relay coil. The polarity of probes on terminals doesn’t matter because we are finding resistance.

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Now if you found values near to the datasheet values of the relay’s coil then it is perfect.

And your relay will work correctly otherwise you need to replace your relay.

## Test the Relay Contacts using Multimeter:

Beside that technique of finding the relay functionality, you can use this method also. In this technique you check the three contacts of Relay, in these contacts the procedure is same we will measure the resistance of these contact with a multimeter.

1. Normally Closed Terminal (NO)
2. Normally Open Terminal (NC)
3. Common Terminal (COM)

### Normally Closed Terminal (NC) Contact:

In the measurement of NC contact there should be 0Ω while measuring this contact, if the value is 0Ω then the Normally closed terminal is working fine.

Procedure:

• Take a multimeter and put it on the ohmmeter settings.
• Place the multimeter one probe on NC terminal and other on COM terminal of Relay
• Note the resistance values
• If you get the resistance value of 0Ω, congratz this terminal is working correctly.

Illustration:

Testing Normally Closed Terminal of a relay with a Multimeter

### Normally Open Terminal (NO):

In the measurement of NO contact there should be the resistance of MΩ, if you find the value of MΩs then this NC terminal is working fine, and the reason behind this is that when NC and COM are not connected there is a huge amount of impendence.

Procedure:

• Take a Multimeter and put it on the ohmmeter settings.
• Place the multimeter’s one probe on NO terminal and other on COM terminal.
• Note the resistance values.
• If you get resistance values of MΩs, congratz this terminal is also working correctly.
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Illustration:

Testing Normally Open Terminal of a relay with a multimeter

Read More: How to Test an Inductor with Multimeter

Conclusion:

In this article, we learned that there are two ways of finding the functionality of relay whether the relay is working well or not. Both ways have one thing common which is checking the resistance of the relay’s terminals. The first method of checking the terminal resistance was useful when you have datasheet available, and another method was also useful when you are making a project based on a relay or you do not have any datasheet available then you can use that method.

Read More: Working of Ammeter and Voltmeter

And if you like our post then please comment below to appreciate or if you find any query regarding the post feel free to comment down below. Thanks

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1. #### Mike Garland

My Mercedes Kompressor C230 is 20 years old. The windshield wiper motor failed, and wondering if my relays could be defective?

I put a rebuilt motor in, and it failed almost immediately. Motor got hot, and it could be defective, but wondering about relay.

New motor shows up in 3 days. So I’ll try again.

• #### Sohailanwar

Hey Mike Garland,
Thanks for your comment, keep visiting StudentsHeart.com

2. #### Muthukumar

Very useful article.thank you so much..

• #### Sohailanwar

Hey MuthuKumar,
Thanks for your comment, keep visiting StudentsHeart.com