An engineer suspects a short in the motor windings has caused the motor to trip on overload. What instrument should be used to check the motor?

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

Answer: (C)

To check for a short in motor windings, you measure the winding resistance with an ohmmeter. An ohmmeter passes a small current through a winding and reports its resistance, so you can spot a short by seeing abnormally low resistance or a mismatch between windings. If windings are healthy, the resistance will be within the expected range; a short between turns or to another winding will pull that value down, often significantly, and can explain an overload trip. While a voltmeter or ammeter can tell you about supply voltage or current, they don’t reveal the internal resistance of the windings. A multimeter can measure resistance too, but the specialized tool for assessing winding continuity and faults is the ohmmeter.