There are three commonly used methods for testing insulation resistance: spot reading test, time resistance test, and step voltage test. These three tests are used primarily to test insulation in motors, generators, cables, transformers, and other electrical apparatus. Additionally, there are two ratio test methods that are also helpful when testing rotating machinery, such as motors and pumps.

To perform these tests, it is best to have a megohmmeter with a timed test function and the ability to select from a range of test voltages. It is also helpful to have a thermometer or similar temperature measurement device on hand. If the equipment temperature is below the dew point, a humidity measuring instrument will be necessary, especially when performing a spot test.