The purpose of this article is to show some general guidelines to perform an Insulation test with a Fluke instrument.
The idea behind using an insulation tool is to verify the coating on the outside of the wire has not lost integrity and shorted to ground or another wire.
A common question when using an Insulation tester is what Voltage level to use. The general rule of thumb is whatever the circuit or motor is rated for you double that voltage when using the Insulation tester. Example if the system is 480V you would set the Insulation tester to 1000V.
Another common question is what ohm read is good or bad. Ideally you would have guidelines from the motor manufacture or Electrical codes to determine good or bad. If you don't have a standard to go by the common rule of thumb is if the level is below 1M ohm that is a failure, the higher the reading above 1M ohm the better the integrity of the wire insulator.
Thirdly if you have not used an Insulation meter before it's a good idea to get familiar with it by creating a short and an open circuit and test both of those situations.
The first thing we are going to do is create a short by plugging the Test probe with the three terminals into the input jack that matches that connector and the red lead into the input below it (see below picture). On the other end of both of those probes attach the alligator clips and join them to create a direct short. Once you've done that push and hold the Yellow Insulation Test button on the meter. The results on the display will show the voltage level at 1V and the resistance level at 0.0M Ohms. Below (left) is a picture of the Fluke-1587 FC showing the test lead probe with an alligator clip and the other test lead with alligator clip shorted together. The other picture (right) is a close up of the screen I circled the test voltage 1000V, the voltage level results 1V and the resistance reading 0.0 M ohm.
The second test is to keep everything the same except to make sure the two test probes are not touching each other and then push and hold the Insulation Test button. The display will indicate the voltage level you selected at bottom right corner of display and the highest ohm value that voltage level can resolve. Below is an example of using the Fluke-1587 FC in the 1000V setting and the maximum level the Fluke-1587 FC can resolve is >2.2 G ohms. If you were connected to a circuit or motor the below results are considered good or anything above 1M ohm to >2.2 G Ohms. If the level was below 1M ohm the rule of thumb is your results are a failed test.
Below is a table created by The International Electrical Testing Association (NETA)