Voltage Drop Calculator

Electrical resistance in wires causes a natural loss of energy over distance. The core formula governing this physics calculation is:

Voltage Drop = (Load Current × Wire Length × Wire Material Resistivity × Phase Coefficient) / Cross-Sectional Area

Once the absolute voltage drop is computed, the percentage drop is found by dividing the drop by the initial source voltage, and the final terminal voltage is determined by subtracting the voltage drop from the initial voltage supply.

Consider a 120-volt circuit supplying power to a remote workshop shed. Suppose you have a load current of 15 amperes, a copper wire length of 100 feet, a cross-sectional area equivalent to standard 12 AWG wire, and a single-phase coefficient. Applying the formula, the electrical resistance of the conductor results in a voltage drop of approximately 3.8 volts. This yields a voltage percentage drop of about 3.17%, leaving the terminal equipment with 116.2 volts, which falls well within the safe operational threshold of 5%.

To minimize electrical losses in your wiring projects, always adhere to these practical guidelines:

1. Upsize Your Wires: If your calculation reveals a voltage drop exceeding 3% for branch circuits or 5% for feeders, step up to a larger wire gauge to reduce resistance.

2. Consider Material Properties: While aluminum is cheaper and lighter, copper offers significantly lower resistivity, meaning it performs better over long distances.

3. Account for Temperature: Higher operating temperatures increase wire resistance, so factor in thermal conditions when planning high-load installations.