This video explains how to check the ground insulation of an AC motor winding using the insulation resistance (IR) test. The IR test is usually the first electrical test because it indicates if the motor winding can withstand further testing, or the machine can return to service. This video shows:

• How to select the megohmmeter and IR test voltage
• How to connect the megohmmeter to the winding and ground the leads
• How to perform the IR test and for how long
• How to safely discharge the winding
• How to correct the IR test result to the standard temperature of 40°C and determine if it is acceptable