HOLT Electricians Practice Exam

What is the permitted circuit breaker size for short circuit and ground fault protection for a 1 horsepower, 120-volt motor with a nameplate current rating of 14 amperes?

1. 30 ampere

2. 35 ampere

3. 40 ampere

4. 45 ampere

The correct answer is: 40 ampere

In determining the permitted circuit breaker size for short circuit and ground fault protection for a motor, the National Electrical Code (NEC) provides guidelines that must be followed. For a motor, the maximum circuit breaker size is generally calculated using the nameplate current rating. For a 1 horsepower, 120-volt motor with a nameplate current rating of 14 amperes, you look at the NEC guidelines regarding overload protection. Typically, for motors, the size of the circuit breaker can be calculated by applying a multiplier to the full-load current value. The NEC often permits a circuit breaker to be sized at 125% of the motor's full-load current rating, particularly in situations where a start-up inrush current may occur. In this case, to find the maximum permissible size for the circuit breaker, the calculation would be performed as follows: 1. Take the nameplate current rating: 14 amperes. 2. Multiply the current rating by 125% (or 1.25): 14 A × 1.25 = 17.5 A. Since circuit breakers come in standard sizes, the next available standard size above 17.5 A would typically be 20 A. However, when considering the maximum allowed for short