Voltage Drop Calculator
Calculate voltage drop, percentage loss, and voltage at the end of the run for copper and aluminum wires.
Why Voltage Drop Matters
Voltage drop occurs when the voltage at the end of a run of cable is lower than at the beginning. This is due to the resistance of the wire. Excessive voltage drop can cause lights to flicker, motors to run hot, and equipment to fail.
NEC Recommendations
The National Electrical Code (NEC) recommends a maximum voltage drop of:
- 3% for branch circuits (from the panel to the device).
- 5% for feeder and branch circuits combined (from the service entrance to the device).
Formula
VD = (K × I × L × 2) / A
(For Single Phase. Use √3 instead of 2 for Three Phase)
Where:
K = Specific Resistance (Copper ≈ 12.9, Aluminum ≈ 21.2)
I = Current in Amps
L = Length of wire
A = Cross-sectional area (Circular Mils)