The Advanced Wire Ampacity Calculator will calculate the maximum ampacity for a wire based on wire gauge, preferred (or available) wire insulation, conductor type and installation specifications. This calculator also provides wire size correction factors for temperature, number of conductors in a raceway, and voltage drop for long wire runs. This calculator is based on NEC (NFPA 70®: National Electrical Code® (NEC®), 2014 Edition) Table 310.15(B)(16-17).

Enter the information below to calculate the ampacity for the selected wire gauge and given conditions.

Maximum Allowable Ampacity -

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.

Wire Size - Choose the size (AWG or kcmil) of the wire for which to calculate the maximum allowable ampacity based on the conditions chosen above in the calculator.

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)

For simpler circuits that do not need temperature or number of conductors correction factors, use the Wire Size Calculator.

For long conductor runs where voltage drop may be an issue, use the Voltage Drop Calculator to determine voltage drop and the Circuit Distance Calculator to determine maximum circuit length. Visit the Tables page to view reference tables such as Maximum Ampacity for Current-Carrying Conductors.