HOLT Electricians Practice Exam

According to the NEC, how should motor overload protection devices be sized?

1. Based on the motor’s horsepower rating

2. Based on the motor’s circuit voltage

3. According to full-load current ratings

4. Based on diameter of motor conductors

The correct answer is: According to full-load current ratings

Motor overload protection devices must be sized according to the full-load current ratings of the motor. This approach is crucial because the full-load current represents the maximum current the motor will draw under normal operating conditions. By sizing overload protection based on this rating, you ensure that the device can adequately protect the motor from overheating due to excessive current while allowing for normal operation without nuisance tripping. Sizing overload protection devices by full-load current ratings helps meet the National Electrical Code (NEC) requirements, which dictate that these devices should be capable of handling the motor's operational load without compromising safety. This method considers the typical performance and characteristics of the motor, ensuring effective protection. Other factors like horsepower, circuit voltage, or conductor diameter might influence various aspects of motor installation and protection, but they do not adequately reflect the current draw and operational dynamics of the motor like full-load current does. Thus, focusing on full-load current ensures that the overload device responds appropriately to actual motor conditions.