Nate Electrical Practice Exam

Open motors are designed to operate at a given temperature rise as indicated on the motor nameplate. What does this mean?

1. Indicates the temp. rise over the surrounding air of a motor when the motor is operating at full-load conditions

2. Indicates the temp. rise of the motor.

3. Indicates the temp. drop of the surrounding air.

4. Indicates the temp. drop of the motor at rest.

The correct answer is: Indicates the temp. rise over the surrounding air of a motor when the motor is operating at full-load conditions

When a motor's nameplate specifies a temperature rise, it is referring to the increase in temperature of the motor above the temperature of the surrounding air when the motor is operating under full-load conditions. This indicates how much hotter the internal components of the motor will become due to electrical and mechanical losses during operation. The specified temperature rise is crucial for ensuring that the motor operates within safe limits. If the temperature rise is excessive, it can lead to overheating and premature failure of the motor components, such as insulation degradation, which could result in short circuits or other malfunctions. By specifying this temperature rise, manufacturers help users understand the thermal limits of the motor in real-world applications, enabling them to implement appropriate cooling measures or ensure sufficient ventilation. The choices centered on temperature drop or the motor's temperature at rest do not relate to the operational considerations of an open motor running at full load. Understanding the operational temperature rise is vital for both the longevity and reliability of motor performance.