Journeyman Electrician Practice Exam

What is the approximate voltage drop on a circuit 200 feet away from the panelboard using size 3 AWG copper conductors with a 80-ampere load?

1. 5.00 volts

2. 6.50 volts

3. 7.84 volts

4. 8.40 volts

The correct answer is: 7.84 volts

To determine the approximate voltage drop on a circuit using size 3 AWG copper conductors with an 80-ampere load over a distance of 200 feet, it is essential to understand how voltage drop is calculated. The formula for voltage drop in a circuit is given by: \[ V_{drop} = \frac{2 \times K \times I \times L}{1000} \] where: - \( V_{drop} \) represents the voltage drop in volts, - \( K \) is the resistivity constant for the conductor material (for copper, it is typically 12.9 ohms per mil foot), - \( I \) is the current in amperes, - \( L \) is the one-way length of the circuit in feet. Using this formula, for a circuit length of 200 feet (which means 400 feet total for the round trip), with an 80-amp load, the calculation would look like this: 1. Determine K for copper: \( K = 12.9 \, \text{ohm} \cdot \text{mil} \cdot \text{ft} \). 2. Plug the values into the formula: - \( V