How can you detect a phase-to-phase short in a three-phase stator during testing?

• A. Measure resistance between each pair of phases; abnormally low interphase resistance or abnormal current indicates a short.
• B. Check oil temperature
• C. Inspect cooling fans
• D. Compare phase voltages to neutral

Answer: (A)

Detecting a phase-to-phase short is done by checking interphase resistance. In a three-phase stator, windings are insulated from each other, so the resistance between any two phases should be relatively similar and fairly high. If two windings have a short, the path between those two phases becomes low resistance, so measuring between that pair will yield a noticeably lower value (often accompanied by abnormal current if the motor is energized).

To test, power off and disconnect the windings, then use a precise ohmmeter to measure resistance between each pair of phases (A–B, B–C, and A–C). Look for one pair with a much lower resistance than the others—that indicates a phase-to-phase short. Options like oil temperature or cooling fans don’t reveal electrical shorts, and comparing phase voltages to neutral isn’t a definitive test for a phase-to-phase fault.