The current relay coil is wired in which location in the circuit?

• A. In series with the run winding
• B. Across the line
• C. In parallel with the start winding
• D. In series with the capacitor and motor

Answer: (A)

The starting relay coil is placed in series with the run winding so its current mirrors the run winding current. At start-up, the run current is high, energizing the coil and keeping the relay contacts closed to include the start winding (and its capacitor) in the circuit, which provides the extra torque needed to start. As the motor speeds up, the run current falls to normal running value, the coil loses enough current to drop out, and the relay opens, disconnecting the start winding. This arrangement ensures the start winding is used only during starting and is removed once the motor is running smoothly. Placing the coil elsewhere (across the line, in parallel with the start winding, or in series with the capacitor and motor) would not reliably sense the motor’s speed or would fail to properly switch the starting circuit.