What does the safe operation line mean for AC speed control motors?

Input power to thep AC speed control motor varies with the load and the speed. The greater the load, and the lower the speed, the higher the motor’s temperature will rise (due to operation at less than peak efficiency). The safe operation line (p. F-22) is a representation of how much heat the motor can safely dissipate through its casing. Therefore, you should only apply a torque load to the motor which is at or below the safe operation line. The motor is capable of continuous operation as long as the case is below 194°F (90°C).