USCG Exam PracticeHand/power tools, measuring instruments, and maintenance
A megohmmeter (megger) is the preferred instrument for testing motor insulation aboard ship because it:
- A. Measures current draw under full load conditions
- ✓ Applies a high DC test voltage to read insulation resistance in megohmsCorrect
- C. Reads true power by combining a current coil and a voltage coil
- D. Measures frequency to verify generator speed before paralleling
Why B is correct
A megger applies a high DC test voltage, typically 500 to 1000 V, and reads insulation resistance in megohms. An ordinary ohmmeter's low voltage is inadequate for detecting insulation degradation in motors, generators, and cables. (NEETS Mod. 3 §1-3; DOE-HDBK-1011 Vol.4 §14-1)