Meggering is a high-voltage insulation resistance test performed on motor windings and electrical components using a megohmmeter to detect deterioration, moisture contamination, or potential failure. This test applies 500-1000 volts DC and measures resistance in megohms, typically requiring values above 1 megohm (1,000,000 ohms) for safe operation. Meggering identifies problems before complete electrical failure occurs.
Testing Standards and Values
EPA and manufacturer standards typically require minimum 1 megohm for motors under 1 horsepower and 5 megohms for larger compressor motors. Testing involves disconnecting the component, selecting appropriate voltage (500V for low voltage, 1000V for larger motors), and recording readings after 30-60 second application. Values below 0.5 megohm indicate moisture or contamination requiring component replacement.
Applications and Timing
Meggering tests compressor motor windings, blower motors, and control transformers to assess insulation condition. Perform testing before attempting to power a motor that has been inactive or exposed to moisture. Historical trending across multiple tests detects gradual insulation degradation. Results guide decisions on motor replacement versus continued operation, preventing catastrophic failure and fire hazards.