HOLT Electricians Practice Exam

What is the maximum setting for a branch circuit protection device on a 5 horsepower 230-volt motor?

1. 25 amperes

2. 30 amperes

3. 35 amperes

4. 40 amperes

The correct answer is: 35 amperes

To determine the maximum setting for a branch circuit protection device on a 5 horsepower, 230-volt motor, it's important to apply the National Electrical Code (NEC) guidelines that pertain to motor branch circuits. The NEC specifies that the branch circuit protection must be rated to accommodate the starting currents of the motor, which can be significantly higher than the normal running current. For a 5 horsepower motor operating at 230 volts, the full-load current (FLC) can be estimated using the formula: \[ \text{FLC} = \frac{\text{Horsepower} \times 746}{\text{Voltage} \times \text{Efficiency}} \] Assuming an efficiency of around 80% (common for standard motors), the calculation would look something like this: \[ \text{FLC} = \frac{5 \times 746}{230 \times 0.80} \approx 25.7 \text{ amperes} \] According to the NEC, branch circuit protection is typically set at 125% of the FLC for motors that are not considered continuous loads. This would lead to a calculated value of approximately: \[ \text{Max protection setting} = 25.7