Voltage Drop Tables by Supply Voltage
Voltage drop is the single most important factor in wire sizing for medium and long conductor runs. The supply voltage directly affects the percentage voltage drop: higher voltages result in lower percentage drops for the same absolute voltage loss. This section provides detailed voltage drop tables organized by supply voltage, with pre-computed values for every standard wire gauge at distances from 25 to 500 feet. Select your circuit voltage below to see the complete reference tables.
Select Your Voltage
120 Volt Circuits
120 volts is the standard household voltage in the United States for general-purpose receptacles and lighting. It is derived from a 240-volt service by using one hot conductor and the neutral. Most re...
View Voltage Drop Tables →Circuits
240 volts is used for large residential appliances and equipment that require more power than a 120-volt circuit can efficiently deliver. A 240-volt circuit uses both hot conductors from the main serv...
View Voltage Drop Tables →Circuits
208 volts is the standard three-phase voltage in commercial buildings supplied by a 120/208V wye-connected transformer. It is lower than 240V because of the 120-degree phase relationship between the t...
View Voltage Drop Tables →Circuits
277 volts is derived from a 480/277V wye-connected transformer and is the standard voltage for commercial and industrial lighting in the United States. Using 277V for lighting reduces the current draw...
View Voltage Drop Tables →Circuits
480 volts three-phase is the standard power distribution voltage in industrial and large commercial facilities. The higher voltage reduces conductor size requirements by a factor of 4 compared to 120V...
View Voltage Drop Tables →Why Voltage Level Matters for Wire Sizing
The supply voltage has a direct and significant impact on voltage drop percentage. Since percentage voltage drop equals the absolute voltage drop divided by the supply voltage, a circuit operating at 240 volts will have exactly half the percentage voltage drop of a 120-volt circuit with the same absolute voltage loss. This is why large appliances like electric ranges, dryers, and air conditioners use 240-volt circuits: the higher voltage reduces current draw by half (for the same wattage), which reduces both the absolute voltage drop and the percentage voltage drop, allowing the use of smaller and less expensive conductors.
For industrial installations, 480-volt three-phase distribution provides even greater advantages. The combination of higher voltage and three-phase power delivery means that conductors can be significantly smaller for the same power capacity. A 100-horsepower motor running on 480V three-phase draws approximately 124 amps, compared to 416 amps on 120V single-phase (if that were even practical). The reduced current means smaller, less expensive conductors, lower voltage drop over long runs, and more efficient power delivery throughout the facility.
When designing electrical systems for new construction, selecting the appropriate distribution voltage is a critical early decision. Residential systems are standardized at 120/240V single-phase, but commercial and industrial facilities have the option of 120/208V three-phase, 277/480V three-phase, or combinations using step-down transformers. The voltage drop tables on each page below help you understand how conductor size requirements change with voltage, informing better system design decisions.
The three-phase voltage drop formula uses a factor of 1.732 (the square root of 3) instead of the factor of 2 used for single-phase calculations. This means three-phase circuits have approximately 13.4% less voltage drop than single-phase circuits with the same conductor size, current, and distance. Combined with the inherently lower per-phase current of three-phase systems, this makes three-phase power distribution significantly more efficient for commercial and industrial applications.
NEC Voltage Drop Recommendations by Circuit Type
The NEC provides voltage drop guidance that varies based on the type of circuit. Understanding these recommendations helps you select the correct maximum voltage drop limit for your calculation:
The NEC recommends that voltage drop on branch circuits (from the last overcurrent device to the load) not exceed 3%. This applies to the final circuit serving the actual equipment or receptacles. At 120V, 3% equals 3.6 volts; at 240V, 3% equals 7.2 volts.
The combined voltage drop of the feeder circuit (from the service entrance to the subpanel) plus the branch circuit (from the subpanel to the load) should not exceed 5% total. This allows the feeder to drop up to 2% if the branch circuits are kept to 3%, or other combinations that total 5% or less.