USCG Exam PracticeElectrical measuring devices and instrumentation
Before using an ohmmeter to measure the resistance of a motor winding, the technician must first:
- A. Set the meter to its lowest resistance range and connect it across the supply terminals
- ✓ De-energize and isolate the circuit, then short the leads and zero-adjust the meterCorrect
- C. Apply the meter leads while the motor is running to obtain a dynamic reading
- D. Connect the meter in series with the winding while the circuit remains energized
Why B is correct
An ohmmeter uses its own internal battery as a source; external voltage on the circuit will give false readings or damage the meter. The leads must be shorted and zero-adjusted before use to compensate for battery aging, and the circuit must be de-energized and isolated.
Cited:NEETS Mod. 3 §1-3