To increase starting torque in a split-phase motor, what is added in series with the start winding?

• A. Capacitors
• B. Resistors
• C. Inductors
• D. Transformers

Answer: (A)

A capacitor in series with the start winding makes the current in that winding lead the applied voltage, creating a larger phase difference between the currents of the start and main windings. That greater phase shift produces a stronger rotating magnetic field at start, which increases the starting torque. After the motor starts, the start winding is typically disconnected by a centrifugal switch (in capacitor-start motors) or the capacitor remains only to sustain torque in capacitor-run designs. A resistor would just waste current and not provide the needed phase shift, an inductor would usually reduce performance by lagging the current, and a transformer isn’t used to achieve this effect.