HOLT Electricians Practice Exam

What size feeder conductor is required for two motors: one rated at 7 ½ horsepower, 230 volts, and another rated at 5 horsepower, 230 volts?

1. No. 2

2. No. 4

3. No. 6

4. No. 8

The correct answer is: No. 4

To determine the correct size feeder conductor for the two motors, you first need to calculate the total amperage that the motors will draw. For a motor, the full load current can be calculated using the formula: \[ \text{Full Load Current (Amps)} = \frac{\text{Horsepower} \times 746}{\text{Voltage} \times \sqrt{3}} \] Since the motors are likely single-phase, the formula simplifies to: \[ \text{Full Load Current} = \frac{\text{Horsepower} \times 746}{\text{Voltage}} \] Now, calculate the current for the 7.5 HP motor: \[ \frac{7.5 \times 746}{230} \approx 24.3 \text{ Amps} \] Next, calculate for the 5 HP motor: \[ \frac{5 \times 746}{230} \approx 16.2 \text{ Amps} \] Adding these together gives: \[ 24.3 + 16.2 \approx 40.5 \text{ Amps} \] In accordance with the National Electrical Code (NEC), when determining feeder conductor sizes, you