NEC Commercial Electrical Practice Test

The load of a single motor on its branch circuit conductors should not exceed what percentage of the conductor ampacity?

1. 100%

2. 110%

3. 125%

4. 150%

The correct answer is: 125%

When evaluating the load of a single motor on its branch circuit conductors, it is essential to consider the motor’s full-load current and its impact on the safety and reliability of the electrical system. According to the National Electrical Code (NEC), the ampacity of conductors must be chosen carefully to ensure that they can handle the expected current without overheating. The NEC stipulates that when calculating the load for a single motor, the conductors should be rated to accommodate at least 125% of the motor's full-load current. This requirement is in place because motors can draw more current than their full-load rating during startup, which can significantly increase the demand on branch circuit conductors. By ensuring the conductors can handle 125% of the motor's rated load, the installation provides a safety margin to prevent overheating and ensures reliable operation. This percentage also accounts for the inrush current that motors experience during startup, which is typically higher than the normal operating current. By adhering to this 125% rule, electricians can effectively ensure that electrical systems remain safe and operate efficiently under their expected loads.