Whether you use a Megger insulation tester monthly, twice a year, or once a year, it is important to be able to interpret the results. Megger insulation tester readings should be considered relative and are known to be quite different with each reading. For example, you may test one piece of equipment three days in a row and get three different readings; however, this does not mean that the equipment has bad insulation.

When using a Megger insulation tester, it’s important to look at equipment reading trends over a period of time. These trends are what will show lessening in equipment resistance and warning of upcoming problems. For this reason, a Megger insulation tester should be used periodically and should be included in scheduled preventative maintenance. When scheduled tests are performed, they should be done in the same way each time. This means that the same test connections and the same voltage should be applied for the same length of time to determine the resistance trends.


When using a Megger insulation tester, it’s important to be familiar with general reading observations and what to do with them. We have created a cheat sheet below to help you get a better idea of readings and what to do with their results.