USCG Exam PracticeElectrical measuring devices and instrumentation
When using an ohmmeter to measure the resistance of a motor winding, the technician must first ensure the motor is:
- A. Running at no-load to stabilize the winding temperature
- ✓ De-energized and isolated from the circuitCorrect
- C. Connected to its normal supply voltage so the meter can reference it
- D. Set to the lowest resistance range before leads are applied
Why B is correct
An ohmmeter uses its own internal battery as a source. Applying it to an energized circuit will produce false readings or damage the meter. The equipment must be de-energized and isolated before resistance measurement.
Cited:NEETS Mod. 3 §1-3