About this calculator This calculator determines the required wire gauge from NEC Table 310.16 based on circuit amperage. It returns the minimum conductor size that meets the ampacity requirement for copper conductors at the standard temperature rating. Use it when specifying branch circuit or feeder wiring for HVAC equipment.
Use when You need to determine the correct wire size for a given amperage.
Formula Wire Gauge = NEC Table 310.16 Lookup (Amperage)
Variables
Amperage Circuit amperage
Amperage (A)
Circuit amperage for wire sizing
Wire Size —
Max Amps —

How is HVAC wire size determined?

Wire size for HVAC equipment is determined by two criteria per the National Electrical Code (NFPA 70): ampacity (the maximum current a conductor can carry without exceeding its temperature rating) and voltage drop (the voltage lost over the length of the conductor run). Ampacity is determined from NEC Table 310.16, which lists allowable ampacities by wire gauge, insulation temperature rating, and conductor material (copper or aluminum). Voltage drop is calculated from conductor resistance, circuit length, and load current. NEC informational notes in Articles 210.19(A) and 215.2(A) recommend limiting voltage drop to 3% on branch circuits and 5% total across feeders and branch circuits combined. For HVAC equipment, wire size must accommodate the Minimum Circuit Ampacity (MCA) listed on the equipment nameplate per NEC Article 440. The conductor is sized to the next standard gauge that meets both ampacity and voltage drop requirements.

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