Three-phase dual-voltage motors are used for most day-to-day operations in today’s industrial plants. Monitoring insulation resistance over time can be a valuable tool in predicting when a motor is headed toward failure and/or requires maintenance. A program of regularly scheduled insulation testing with a megohmmeter can increase motor safety by minimizing the risk of electric shock and electrical fire. This Application Note reviews insulation testing for three-phase dual-voltage motors. We look at different motor types, methods for testing them, which megohmmeters to use for which types of testing, and questions to consider when setting up your own insulation testing program.