What Is Dielectric Testing?

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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