A maintenance tech uses a megohmmeter to test a 480V 3-phase pump motor. The reading from phase A to ground is 0.5 MΩ. What should the tech conclude?
Answers
AThe reading is acceptable if the motor is warm
BThe motor is in perfect condition and ready to run
CThe motor insulation is severely degraded and the motor should be removed from service
DThe tech should use a multimeter instead of a megohmmeter
Correct answer: C — The motor insulation is severely degraded and the motor should be removed from service
For a 480V motor, insulation resistance should generally be >1 MΩ. A 0.5 MΩ reading indicates significant insulation breakdown or moisture ingress.
MIFOTRA exam practicealigned to NFPA 70 / IEC 60364·3 marks·Medium