Wire Size by Application

Residential and Single-Phase Applications

These are the most common electrical circuits found in residential homes, garages, workshops, and small commercial buildings. All use single-phase power at 120 or 240 volts. Selecting the correct wire gauge is critical for safety and NEC compliance. For longer runs to detached structures like garages, sheds, and outbuildings, voltage drop becomes the primary concern and often requires upsizing the conductor beyond what ampacity alone would require.

Commercial and Three-Phase Applications

Commercial and industrial electrical circuits often use higher voltages (208V, 277V, 480V) and three-phase power to reduce conductor sizes and improve motor efficiency. Wire sizing for these applications must account for the three-phase voltage drop formula, which uses a factor of 1.732 instead of 2. Higher voltages also result in lower percentage voltage drop for the same absolute voltage loss, allowing longer conductor runs.

How to Use These Application Pages

Each application page provides a complete wire sizing reference for that specific circuit type. You will find the recommended wire gauge for copper and aluminum conductors at distances ranging from 25 feet to 500 feet, with voltage drop calculations at each distance. The pages also include the applicable NEC code references, installation tips specific to that application, and common mistakes to avoid.

The wire sizes shown are calculated using the standard voltage drop formula with NEC Chapter 9, Table 8 resistance values for uncoated conductors at 75 degrees C. Both the ampacity requirement (from NEC Table 310.16) and the voltage drop recommendation (3% for branch circuits, 5% for feeder plus branch combined) are checked, and the larger of the two determines the final recommendation. This ensures that the recommended wire size is both safe and efficient for the specified application.

Keep in mind that these are general recommendations based on typical installations. Your specific installation may have additional requirements such as ambient temperature derating, conduit fill derating, continuous load factors, or local code amendments that affect the wire size. Always consult the NEC and your local authority having jurisdiction (AHJ) for the final determination. When in doubt, hire a licensed electrician who is familiar with your local codes and can evaluate the specific conditions of your installation.