MotorsQuestion 1279 of 1506

A three-phase motor must be run from a single-phase supply. What is needed to get it started?

  1. A larger winding added in the stator slots by the electrician
  2. A resistor placed in the supply line
  3. A DC field supply connected to the rotor
  4. A starting capacitor feeding the third winding in series
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Correct answer: A starting capacitor feeding the third winding in series

The capacitor makes a made-up second phase for starting. After the start, the motor can keep running on single phase.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 13.7: Tesla Polyphase Induction Motors

Practice motors

Questions last reviewed: 18 October 2026