Voltage Drop & Wire Size
Calculate voltage loss in electrical cables based on length, AWG size, and material (Compliant with NEC Standards).
Calculation Results
What is Voltage Drop?
Electrical cables are not perfect conductors; they have a natural inherent resistance to the flow of electricity. When power is transmitted over long distances, this resistance causes a portion of the voltage to be lost as heat before reaching the load. This phenomenon is known as voltage drop.
If the voltage drop is too high, motors will lose torque and run hotter, lighting will flicker or dim, and sensitive electronic equipment may fail or experience unexpected reboots due to undervoltage.
NEC Standards & Maximum Allowable Limits
The National Electrical Code (NEC) provides strict guidelines for electrical design to ensure safety and efficiency. According to NEC Article 210.19(A) Informational Note No. 4:
- Branch Circuits: The maximum recommended voltage drop is 3% at the farthest outlet.
- Feeders + Branch Circuits: The total combined voltage drop should not exceed 5%.
- Solar PV Systems: For solar panels, it is often recommended to keep the drop below 1.5% - 2% to maximize energy yield.
Voltage Drop Engineering Formula
This calculator determines the loss using the standard engineering formula based on the conductor's specific resistivity, length, and cross-sectional area. The formula used for a single-phase AC or DC circuit is:
Where:
- Vd = Voltage Drop (Volts)
- L = One-way length of the circuit (converted to meters internally)
- I = Load current (Amps)
- ρ = Specific resistivity of the material (0.0172 for Copper, 0.0282 for Aluminum at 20°C)
- A = Cross-sectional area of the wire in mm² (mapped from AWG)
Note: For three-phase circuits, the multiplier "2" is replaced by the square root of 3 (approx. 1.732).
How to fix an excessive voltage drop?
The most direct and common engineering solution is to increase the wire size (decrease the AWG number). By using a thicker wire, you reduce its ohmic resistance, allowing current to flow with much less loss. Another alternative for extremely long distances is transmitting the power at a higher voltage and using step-down transformers at the destination.