Megger readings are the result of an insulation test. The term Megger is also known as the insulation resistance test or IR test. Megger readings vary and are used to track the insulation manufacturing process to catch any problems that may need to be resolved before they are outside of the allowed limits. Megger readings also check the condition of the insulation and to find the highest point of resistance.
This is a method that has been used for a very long time, and it is still the best available option because it does not cause any deterioration of the insulation. There are a number of testers available that range from 500 to 2500 volts. There are also different equations that determine the reading, and those equations depend on whether or not AC voltage or DC voltage is being used.
When testing, it is very important to take precautions. Be sure to test the equipment before it is used and make sure that all of the connections in the test circuit are tight so that you get the best reading. The actual resistance values can be higher or lower, depending on factors such as temperature or moisture content of the insulation.