Single-Phase Three-Phase

60°C 75°C 90°C

Copper Aluminum

Raceway Cable Burried in Earth Open Air

70-77°F 78-86°F 87-95°F 96-104°F 105-113°F 114-122°F 123-131°F 132-140°F 141-158°F 159-176°F

1-3 4-6 7-9 10-20 21-30 31-40 > 40

1% 2% 3% 4% 5%

Calculate Reset

Voltage - Enter the voltage at the source of the circuit. Single-phase voltages are usually 115V or 120V, while three-phase voltages are typically 208V, 230V or 480V.

Amperes - Enter the maximum current in amps that will flow through the circuit. For motors, it is recommended to multiply the nameplate FLA by 1.25 for wire sizing.

Phases - Select the number of phases in the circuit. This is typically single-phase or three-phase. For single-phase circuits, three wires are required. For three-phase circuits, four wires are required. One of these wires is a ground wire which can be sized down. To calculate ground wire size, use the Ground Wire Size Calculator.

Insulation - Select the thermal rating of the insulation on the wire.

Conductor - Choose the material used as a conductor in the wire. Common conductors are copper and aluminum.

Installation - Choose the installation method for the circuit. This is typically in a raceway (cable-tray or conduit), in a cable, burried in the Earth, or in open air.

Voltage Drop - Choose the maximum percentage of the source voltage drop. It is recommended not to exceed a voltage drop of 5%.

Distance - Enter the one-way length of the wires in the circuit in feet.

Note: It's recommended to check the ampacity of a wire after doing a voltage drop calculation. Always use the total length of the circuit for calculations. Consult with an engineer if your application requires more complex calculations.

Source: NFPA 70, National Electrical Code, Table 310.15(B)(16-17)