Which instrument is specifically used to measure electrical resistance to diagnose winding faults in motors?

• A. Ohmmeter
• B. Ammeter
• C. Voltmeter
• D. Multimeter

Answer: (A)

Measuring the resistance of motor windings is best done with an instrument that directly reads electrical resistance. An ohmmeter does just that: it applies a small test current and measures the resulting voltage drop to calculate resistance. This direct reading lets you see if a winding is open (very high or infinite resistance), has degraded insulation or contact (abnormally high resistance), or may have a shorted turn or parallel path (abnormally low resistance). By comparing the measured resistance to the motor's specified winding values, you can diagnose winding faults effectively.

Ammeters gauge current, not resistance, so they won’t reveal winding integrity. Voltmeters measure voltage, not resistance. A multimeter can measure resistance as one of its functions, but a dedicated ohmmeter provides a more straightforward, focused resistance test for winding faults and is the standard tool for this purpose. Always power off and isolate the winding before testing.