Skip to content
An Unbound Renewable Energy Company
Open Mon-Fri: 6am to 5pm PST
Use this voltage drop calculator to find the right wire size for your solar electric system.

Voltage Drop Calculator

k=12.9 for copper or k=21.2 for aluminum
Voltage Drop:
Percentage of Voltage Drop
Voltage at Load End of Circuit:
CMA of Conductor:

What is Voltage Drop?

FREE Solar Inverter Guide
When an electrical current moves through a circuit, a small amount of voltage is lost due to resistance in the wires. This concept, known as voltage drop, leads to a slight production loss from your solar array.

When you go solar, one of the goals is to minimize voltage drop so that your system performs at peak efficiency. This voltage drop calculator is a tool to help plan your wiring run and get as much production as possible from your array.

How to Use the Voltage Drop Calculator


  • Material: Choose from aluminum or copper wire.
  • Size: The size of the wire. (Larger wire = less voltage drop.)
  • Phases: Choose an inverter that matches the configuration of your local utility service.
  • 1-way circuit length: Length (in feet) of your circuit. This is the distance between your array and your inverter, or your inverter and the service panel.
  • Load: Total input (in amperes) from appliances powered by the PV array.
    Voltage (max): The max input voltage of your service panel. 240V is standard.


  • Voltage Drop: Power lost (in volts) over the length of the wiring run.
  • Voltage Drop %: Power lost to voltage drop as a percentage of total power generated.
  • Voltage at Load End of Circuit: Voltage at the end of the circuit (after current has passed through the wire and voltage drop has occurred).
  • CMA of conductor: Stands for Circular Mil Area. Measures the area of the selected wire size.

How to Minimize Voltage Drop

The current NEC (National Electric Code) recommends systems should be designed with less than 2% voltage drop. In most cases, a properly-designed solar system should come in well under that mark.

Here are some tips to help you reduce voltage drop and get the most out of your array:

  • Put your components close together to minimize the length of the wiring run. Longer wires = more resistance, which translates to higher voltage drop.
  • Use a bigger wire size. Larger wire = less resistance.
  • If a long wiring run is necessary, design your system to overcome resistance. Use high-voltage products and large panel strings (if you’re using a string inverter).

Feeling stuck on system design? Request a free consultation with our design team, or call us up at 1-800-472-1142 to connect with us immediately. Every system we sell includes an electrical wiring diagram designed to minimize voltage drop and ensure your system is up to code.

Download Your FREE Solar Inverter Guide

Manage Power Flow Like a Solar Pro! Download Now for Hassle-Free Hookup.