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How to Test A Transformer Without Power: Check These 3 Things

While buying a transformer there are a lot of factors you have to check. Sometimes you need to check the transformer without power before testing it with power. I know many of us didn’t even know that it was possible.

How to test a transformer without power?

Well, there are different tests that you can do on the transformer without power. Firstly you can test if there is a short circuit between the core and the cables. Then check for short-circuits between the thick and thin wires. You have to check for any breakage in these wires too.

This is only the starting. You have to know the accurate procedures to complete the tests.

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How to Test a Transformer Without Power 

It is very important to check the transformers before bringing them home. No one wants to change a faulty product once it is brought home. So it’s better to check beforehand.

There are different types of tests available for transformers like the continuity test and others. On a larger scale, all the tests can be divided into two types.

They are with power and without power. Both tests are important to ensure the working ability of the transformer. We will discuss the tests you can do without power here. 

You will need an ohmmeter to conduct the test. A multimeter will do the job too as it is a combination of an ohmmeter, voltmeter, and ammeter. Once you get the meter you can easily conduct the test by yourself.

Short-Circuit Check of The Transformer Core

Checking for short connections is very important for any electrical circuit. Short connection means the situation where the power will not flow according to the designed circuit. Rather it will go in other ways. 

This problem happens if any wire gets in touch with another wire or any conductive substance. Short circuit connections can cause a fire. It can damage the transformer permanently. The core can be shortened too. It occurs if it has an unknown connection with any of the wires of the transformer.

Take the multimeter. Keep its range at 200 ohms. There are two pins of the meter. The colors of the pins are different to make the work simple. They are usually black and red.

Keep one pin on the core of the transformer. Connect the other pin with the thick cable. If the reading on the meter is infinite, the transformer is not shorted with the thick wire.

Then repeat the process with the thin wire. The result should be the same as before. Did you get infinity on the multimeter screen? It means the transformer is not shorted with the thin wire too.

Short-Circuit Check of The Transformer Wires 

Once you have checked the short between core and wire, it is time to check the wires. Any short-circuit connection between the thin and thick wire must be avoided. Short circuits are one of the most common electrical problems. So let’s see how to check them.

Keep one pin on the thin wire and the other one on the thick wire. Now check the multimeter reading. The result should be infinity. If it shows any other value the multimeter has a short circuit between the wires.

We have some suggestions of ohmmeters that you can use to test transformers. Check them out:


These products are very simple and easy to use. We are sure that you will like our recommended products once you use them. 

Wire Breakage Test

Wire breakage means a gap or fault in the wire. Due to wire breakage, the current will not flow properly. So you must check if the current will flow perfectly through the thick and thin wires. This test is also known as the continuity test.

We will use the multimeter for this test too. Set one pin of the meter on one end of the thin wire. Then connect the other pin with the end that is free.

The multimeter will give a reading if the wire has no connection break. This process is the same for any transformer like testing a 24-volt transformer

Do the same with the thick wires. If the wire connection is broken free you will get a reading. This reading is proof that there is no break in thick wires. Since the thick wires should be short, you will get the reading ‘zero’. And that is alright.

These are the tests you can perform on the transformer without power. You will get some important information from these tests. Follow the instructions to do the tests without any error. 


Question: How do you test a transformer to see if it is bad?

Answer: There are several ways of testing a transformer to see if it’s bad. Do the tests with an ohmmeter when the transformer is powerless. Then check the voltage input and output with a source of power.

Question: What happens if you overload a low voltage transformer?

Answer: Overloading a transformer will damage it. This damage takes place due to the increase of temperature of the windings of it. Once the temperature gets out of the limit of insulation the transformer will malfunction.

Question: How do you protect a transformer from overload?

Answer: Transformers can be protected by using the thermal overload delay method. This is a dedicated protection system for the transformer. 


We hope that now you have understood how to test a transformer without power. 

Test the meter before starting the transformer test. 

These powerless tests are completely safe. But you have to be very careful while carrying out the tests with power.

Good luck!