Figure 2-34 shows typical torque-speed curves for single-phase AC motors of various designs. The single-phase shaded pole and permanent split capacitor designs have a starting torque lower than their full-load torque. To boost the start torque, the split-phase and capacitor-start designs employ a separate starting circuit that is cut off by a centrifugal switch as the motor approaches operating speed. The broken curves indicate that the motor has switched from its starting circuit to its running
circuit. The NEMA * three-phase motor designs B, C, and D in Figure 2-34 differ mainly in their starting torque and in speed sensitivity (slope) near the full-load point