USCG Exam PracticeElectrical measuring devices and instrumentation
Megohmmeter readings taken on the same motor over successive maintenance periods show a steady downward trend even though each individual reading still exceeds the minimum acceptable value. The correct action is to:
- A. Accept the readings as satisfactory since they remain above the minimum and schedule no additional action
- B. Immediately rewind the motor because any downward trend indicates imminent failure
- ✓ Treat the downward trend as a warning of progressive insulation deterioration, investigate the cause, and increase monitoring frequencyCorrect
- D. Disregard the trend because megohmmeter readings vary randomly with ambient conditions and have no predictive value
Why C is correct
Trending megger readings over time is a key predictive-maintenance practice. A steadily falling trend warns of gradual insulation degradation from moisture, contamination, or breakdown even before a single reading falls below the minimum threshold. The trend itself is actionable information requiring investigation and increased surveillance.