The Voltage Drop Calculator will calculate the voltage drop across a circuit for long wire runs based on voltage, current, phases, conductor, wire size, and circuit distance. It will also calculate the voltage at the load, and the percent voltage drop.
Enter the information below to calculate voltage drop across a circuit.
Voltage drop is calculated using the most universal of all electrical laws: Ohm's Law. This states that the voltage potential across the conductor is equal to the current flowing through the conductor multiplied by the total resistance of the conductor. In other words, $Vd\; =\; I\; x\; R$. A simple formula was derived from Ohm's law to calculate the voltage drop across a conductor. This formula can help you determine voltage drop across a circuit, as well as the size wire gauge you will need for your circuit based on the maximum desired voltage drop. The National Electrical Code states that the voltage drop of a feeder circuit must not exceed 5%, and the voltage drop of a branch circuit must not exceed 3%.
Voltage drop is calculated for single-phase circuits as follows:
Vd = | 2 x K x L x I |
Cm |
Vd = Voltage Drop
I = Current in Conductor (Amps)
L = One-way Length of Circuit (Feet)
Cm = Cross Section Area of Condcutor (Circular Mils)
K = Resistance in ohms of 1 circular mil foot of conductor.
Note: K = 12.9 for Copper conductors at 75°C (167°F), and K = 21.2 for Aluminum conductors at 75°C (167°F).
Voltage drop is calculated for three-phase circuits as follows:
Vd = | 1.73 x K x L x I |
Cm |
Vd = Voltage Drop
I = Current in Conductor (Amps)
L = One-way Length of Circuit (Feet)
Cm = Cross Section Area of Condcutor (Circular Mils)
K = Resistance in ohms of 1 circular mil foot of conductor.
Note: K = 12.9 for Copper conductors at 75°C (167°F), and K = 21.2 for Aluminum conductors at 75°C (167°F).
To calculate the maximum distance of a circuit based on percent voltage drop, use the Circuit Distance Calculator.
To calculate wire size for a circuit, use the Wire Size Calculator or the Advanced Wire Size Calculator. To calculate wire ampacity for a circuit, use the Wire Ampacity Calculator or the Advanced Wire Ampacity Calculator.
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