What does the light bulb test help identify?

• A. It measures the insulation resistance between windings
• B. It identifies which coils have induced voltage (light flashes)
• C. It determines the motor's rpm
• D. It checks the winding continuity

Answer: (B)

The light bulb test is used to see which windings are experiencing induced voltage from the rotating magnetic field. By connecting a lamp to each coil and rotating the rotor (or energizing the field and moving the windings), you’ll see the lamp light only on the coils that have induced voltage. That visual indication helps identify which coils are being coupled to the field and are producing EMF, rather than anything about insulation, rpm, or just continuity.

So, it’s not about insulation resistance, measuring speed, or simply checking if windings are continuous. It’s a quick way to pinpoint which coils have induced voltage by watching where the light flashes.