A Megger (insulation resistance tester) is a type of electrical test equipment used to verify the effectiveness of insulation to act as a barrier between energized conductors, or between energized conductors and ground. It is critical to the reliability of the electrical power system that there is a way to know when insulation has been damaged or compromised in any way.
While there are ways to electrically stress insulation, insulation resistance testing is typically focused on characterizing the insulation rather than stressing it. Therefore, these type tests are normally performed at voltage levels that are lower than the rating of the insulation and generally much less than if the intent was to stress the insulation.
It is always a good practice to be familiar with the designed limitations of the insulation along with the proper voltage at which to perform the test. This knowledge will help to ensure that the insulation is not damaged or compromised as a result of this type of testing,
Insulation resistance test sets will range in their output capabilities from as little as 50 V dc to as much as 15 kV dc. When too much voltage is used on a test object, it is possible to degrade the insulating quality of the material and contribute to its premature failure once it has been placed back into service. Therefore, it is very important to select a Megohmmeter whose output capability is appropriately matched to the rating of the materials for which it will be used to test.
One of the biggest advantages to using Megger test equipment is that it ensures the safety and usability of electrical equipment without destroying it. However, to make sure that the apparatus still works properly when testing is through, it’s essential that the Megger test set is used properly, and the appropriate voltage is used during the testing process.
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Editor’s Note: This post was originally published May, 2012 and has been updated freshness, accuracy and comprehensiveness.