USCG Exam PracticeHand/power tools, measuring instruments, and maintenance
A megohmmeter (megger) applies a high DC test voltage to measure insulation resistance. Before taking a reading on a motor winding, the watchstander must ensure the equipment is in which condition?
- A. Energized and under full load so the reading reflects operating conditions
- ✓ De-energized and capacitance discharged before and after the testCorrect
- C. Running at no-load with the circuit breaker open on the load side only
- D. Connected in parallel with a known resistance to calibrate the scale
Why B is correct
NEETS Mod. 3 §1-3 states that readings are taken with the equipment de-energized and capacitance discharged afterward. Applying megger voltage to an energized or charged circuit produces false readings and risks damaging the instrument or injuring personnel.
Cited:NEETS Mod. 3 §1-3