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How to Test Wire Insulation Using a Megohmeter

To conduct the test, submerge the cable in water. While submerging the cable, make sure to keep both ends of the cable dry and out of the water. Since air acts as an insulator and water is partially conductive, if there is a breakdown in insulation in the wire cable, electricity will leak into the water and can be detected by a megohmmeter.

Place one probe in the water, and another probe on one of the ends of the wire. The readings should result in very large numbers. If not, the electricity is being leaked into the water, likely from a nick in the installation.

So, what’s a high ohm reading?

With the megohmmeter set to either 500 or 1000 VDC output, normal insulation resistance readings for drop cable and a motor (if attached) should read two-million ohms or more. If the reading is below two-million ohms, it is not recommended to use this wire. Reference Franklin Electric’s AIM Manual as needed for insulation resistance readings.

Click here for the Franklin Electric’s AIM Manual