Voltage Drop Calculator
Ensure your electrical installations are code-compliant. Calculate the voltage drop for any wire run to prevent equipment damage and fire hazards.
Circuit Parameters
Length of wire run from source to load.
Voltage Drop Formula
This calculator uses the standard electrical industry formula based on resistance (K-method):
Single Phase: VD = (2 × K × L × I) / CM
Three Phase: VD = (1.732 × K × L × I) / CM
Three Phase: VD = (1.732 × K × L × I) / CM
- K: Resistivity Constant (12.9 for Copper, 21.2 for Aluminum).
- L: Length of the conductor in feet (one way).
- I: Current in Amps.
- CM: Circular Mils (area of the wire, from NEC Table 8).
NEC Recommendations
Maximum 3% Drop (Branch)
The NEC (Fine Print Note) generally recommends no more than a 3% voltage drop for branch circuits (e.g. from the panel to the outlet) to ensure proper operation of lights and motors.
Maximum 5% Drop (Total)
The total drop including the feeder (from service to panel) + branch circuit should generally not exceed 5%.
Frequently Asked Questions
Frequently Asked Questions
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