HOLT Electricians Practice Exam

What is the VA input for a dual voltage 5 horsepower 3-phase motor rated at 460/230 volts?

1. 4050 VA

2. 5050 VA

3. 6055 VA

4. 7050 VA

The correct answer is: 6055 VA

To calculate the VA input for a dual voltage 5 horsepower 3-phase motor, it is essential to use the formula that converts horsepower to volt-amperes (VA). The formula for calculating the full-load current (I) for a 3-phase motor is: \[ I = \frac{P \times 1000}{\sqrt{3} \times V} \] Where: - P is the power in horsepower - V is the line voltage - The factor of 1000 converts horsepower to watts - The square root of 3 accounts for the three-phase power system's relationship between voltage and current. For a 5 horsepower motor, converting to watts gives: \[ 5 \, \text{hp} \times 746 \, \text{W/hp} = 3730 \, \text{W} \] In a three-phase system, we need to consider the voltage at which the motor operates. For the rated voltage of 460 volts, we can substitute the values into the formula: \[ I = \frac{3730}{\sqrt{3} \times 460} \] Calculating that gives: \[ I \approx \frac