What is an acceptable voltage drop percentage?

The National Electrical Code (NEC) recommends a maximum voltage drop of 3% for branch circuits and 5% for the entire system (feeder + branch) to ensure equipment operates safely and efficiently.

How does wire size affect voltage drop?

Thicker wires (lower AWG numbers) have lower electrical resistance. Therefore, increasing the wire size reduces the voltage drop over long distances. If your voltage drop is too high, selecting a lower AWG wire in our calculator will fix it.

What is the difference between Copper and Aluminum wires?

Copper is a better conductor of electricity than aluminum. Aluminum has about 1.6 times more electrical resistance than copper, meaning you will need a thicker aluminum wire to carry the same current as a copper wire over the same distance.

Electrical Engineering Tool

Voltage Drop Calculator

Quickly compute voltage drop percentage, end voltage, and wire gauge requirements for DC and AC electrical circuits based on NEC guidelines.

Conductor Material

Copper Aluminum

System Type

Voltage (V)

Current (Amps)

Distance (Feet)

Wire Size (AWG)

Voltage Drop

0.00%

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Voltage Dropped: 0.00 V

Voltage at End: 0.00 V

Power Loss (Heat): 0.00 W

What is Voltage Drop?

The Voltage Drop Calculator by AJAI Tech Solutions is designed for electricians, solar panel installers, and electrical engineers. As electrical current travels through a wire, the inherent resistance of the metal (Copper or Aluminum) causes a loss of voltage. This phenomenon is known as "Voltage Drop".

If a wire is too thin (high AWG) or the distance is too long, the voltage reaching your equipment might drop below the required operating threshold, causing motors to overheat, lights to dim, or electronics to malfunction.

NEC Compliance

The National Electrical Code (NEC) recommends a maximum voltage drop of 3% for branch circuits to maintain safe and efficient operation.

Solar & DC Systems

In low-voltage 12V or 24V DC systems (like Solar or RVs), even a 1-volt drop is massive. Calculating wire size is critical here.

How to use the Voltage Drop Calculator

Material: Choose between Copper (standard) or Aluminum. Aluminum has higher resistance.
System Type: Select DC (Battery/Solar), AC Single-Phase (Household), or AC Three-Phase (Industrial).
Voltage & Current: Enter the source voltage (e.g., 120V or 12V) and the load current in Amps.
Distance: Enter the one-way distance of the cable in Feet. The calculator automatically doubles this for DC and Single-Phase AC to account for the return path.
Wire Size (AWG): Select the American Wire Gauge you plan to use. If the drop is > 3%, select a thicker wire (lower AWG number).

Frequently Asked Questions (FAQs)

For DC and Single-Phase AC, the formula is:
V_drop = (2 × Distance × Current × Resistance) / 1000.
For Three-Phase AC, the formula is:
V_drop = (1.732 × Distance × Current × Resistance) / 1000.
The resistance value depends on the AWG size and metal type.

If your voltage drop exceeds the recommended 3%, you have two options: 1. Increase the wire size (choose a lower AWG number, like changing 14 AWG to 10 AWG). 2. Decrease the distance between the power source and the load.

DC systems usually operate at much lower voltages (12V or 24V). A 1V drop on a 120V system is only 0.8%, which is unnoticeable. But a 1V drop on a 12V solar system is an 8.3% loss, which can prevent an inverter or appliance from turning on. Therefore, DC circuits require much thicker cables.