HOLT Electricians Practice Exam

What branch circuit protection device is required for a 2 horsepower 120 volt wound rotor motor?

1. 30 amperes

2. 40 amperes

3. 50 amperes

4. 60 amperes

The correct answer is: 40 amperes

To determine the correct branch circuit protection device for a 2 horsepower, 120 volt wound rotor motor, it is essential to consider the full-load current rating for the motor, which directly influences the required size of the protection device. For a 2 horsepower motor operating on a 120-volt system, the full-load current can be calculated using standard motor full-load current tables or the formula: Full-Load Current (Amperes) = (Horsepower x 746) / (Voltage x Efficiency x Power Factor) Generally, for a 2 horsepower motor at 120 volts, you would expect a full-load current around 20-25 amperes. However, the protection device needs to account for inrush currents during startup, which can be significantly higher than the full-load current. According to the National Electrical Code (NEC), the branch circuit protection for motors can be sized based on the specified overcurrent protection guidelines. For most motor applications, it is recommended that the overcurrent device be sized at 125% of the motor's full-load current for continuous duty. In this context, a 40-ampere protection device would provide adequate protection for a 2-hp motor running at 120 volts while also accommodating