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What is Dielectric Testing?

By T. L. Childree
Updated May 17, 2024
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Dielectric testing is a evaluation process performed by applying a voltage to an electrical component that exceeds its normal operating voltage. The purpose of the test is to determine if a component’s insulation is adequate enough to protect the user from electric shock. This testing procedure is typically performed on electrical components, such as circuit boards, appliances, cables, transformers, and electric motors. The manufacturer of an electrical component typically conducts the testing at the end of the production process, using a special device known as a dielectric tester.

Almost all electrical components leak a certain amount of electrical current due to a variety of different factors. This very small amount of current is considered to be safe for users, but under certain conditions, the insulating materials or mechanisms can breakdown and allow dangerous amounts to come into contact with the user. This type of insulation failure can sometimes cause serious injury or death. Dielectric testing is necessary to ensure that the insulating mechanism of an electrical component will withstand voltage variations under normal operating conditions.

The most common type of testing is the dielectric breakdown test. In this procedure, a high voltage electrical current is applied to the component. The dielectric tester monitors the amount of current leakage during the test to determine if the insulation has failed. The high voltage current continues to be applied to the device until the insulation fails or the time limit of the procedure has been reached. If the insulating mechanism does not fail, the product is usually considered to be safe for use. Electrical components that fail during dielectric testing are typically redesigned in order to meet safety requirements.

In addition to the dielectric breakdown test, a procedure known as a dielectric withstand test is also conducted to determine if defects have occurred during the manufacturing process. Electrical components sometimes contain small flaws, such as gaps or spaces that can create an electrical short circuit during the normal operation of a device. Dirt, humidity, environmental contaminates, and vibration can combine to produce an electrical shock hazard if these manufacturing flaws go undetected prior to consumer use. In this procedure, electrical current is supplied to the component at normal operating voltage. A dielectric tester is attached to the component to monitor the amount of current leakage present. If the leakage levels are within an acceptable range, the component is approved for use.

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Discussion Comments

By andyglean — On Mar 27, 2014

I have a bunch of gloves that I was told to have tested. Any recommendations of a company/place where I should send to be tested? What is typical turnaround time?

By anon314241 — On Jan 16, 2013

I do dielectric testing on components that I build at work. The voltage varies from 500 volts to around 2000 volts, but often it's around 1000 volts DC.

What I really wanted to know is, I test coil assemblies which are insulated around the bobbin and then insulated around the diameter after winding and soldering. If the the dielectric test passes, but a separate insulation resistance test fails, what exactly has failed?

By anon257379 — On Mar 26, 2012

Dielectric tests are generally considered to be "destructive" tests, and are usually performed only when a possible defect may be suspected.

By hamje32 — On Sep 10, 2011

@Mammmood - No, I doubt that very much. As I mentioned, I believe these voltages and the tests are fine tuned to the specifications of the components. They are meant to test the components, not destroy them.

By Mammmood — On Sep 10, 2011

@hamje32 - I wonder if the very act of applying the high voltage test would, in itself, cause the components to experience added wear and tear?

By hamje32 — On Sep 09, 2011

@David09 - The article doesn’t say what the voltages are for the high voltage testing.

I wouldn’t think it would be absolute values across the board as you suppose. Rather, I believe these would be individual tolerance values that would vary depending on the kind of components you are testing. Different components can handle different voltages.

Also, from what I gather in the article, I assume that the tester is testing the pathways between individual components as well. If this is the case, you will definitely have variations in the voltage, because the current may go through components like resistors which would reduce the amount of available voltage.

I’m not an expert, but that’s just what I would guess would happen.

By David09 — On Sep 08, 2011

I would think that insulation testing would have limits on the amount of voltage applied, even in a high voltage scenario. Otherwise, any piece of testing equipment would fail, regardless of the strength of the insulation.

While it’s not stated in the article, I am guessing that by “high voltage” we are talking maybe 240 volts or so; in other words, double what you normally expect from an electrical outlet.

I don’t think it means the kind of surge you might get from a lightning strike. Nothing can withstand that kind of current.

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