Voltages must be within what percentage of the motor rating?

The correct choice indicates that the operating voltages for a motor should ideally be within 10% of the motor's rated voltage. This standard is important because operating outside of this range can lead to various operational issues, including reduced efficiency, overheating, and possible damage to the motor over time.

Maintaining a voltage within this specified range ensures that the motor can run effectively and safely at its designed capacity. A deviation beyond this threshold can result in insufficient torque generation, which can compromise the motor's performance and longevity.

In practical applications, exceeding the acceptable voltage limits can cause excessive current draw and ultimately lead to motor failure, while staying too far below the rated voltage might not provide enough power for the motor to operate effectively. Thus, adhering to the 10% variance helps maintain both efficiency and mechanical integrity in motors across various HVAC applications.