60 °C column
Use only when the conductor/equipment termination rules require the 60 °C ampacity basis. A conductor with 90 °C insulation does not automatically permit sizing from the 90 °C ampacity column.
NEC Cable Sizing Calculator
Size conductors using NFPA 70 (NEC) Article 310 ampacity concepts, ambient correction, current-carrying-conductor adjustment, voltage-drop check and OCPD coordination.
01 · Load & circuit
Define the branch or feeder operating point.
02 · Conductor & installation
NEC ampacity depends on conductor material, temperature column and installation corrections.
Select the ampacity temperature column permitted by the actual conductor insulation and equipment termination ratings. This calculator does not infer terminal temperature limitations for you.
Ready to calculate.
Worked example included
480 V, 3-phase, 52 A continuous load, 180 ft one-way, copper, 75 °C column, 40 °C ambient, 4–6 current-carrying conductors, 70 A OCPD, 3% voltage-drop target. Click “Load worked example” to populate the inputs and calculate the first standard conductor that passes corrected ampacity, voltage drop and OCPD coordination.
How the NEC workflow is applied
The calculator first determines required ampacity from load current and the selected continuous-load multiplier. It then checks each standard conductor size against the selected ampacity column, ambient-temperature correction, current-carrying-conductor adjustment, any project factor, voltage-drop target and the entered protective-device rating.
75 °C column
Common for equipment and conductor combinations rated for 75 °C terminations. Confirm the actual equipment listing and applicable NEC rules before using it.
90 °C column
Often used as the starting ampacity for correction/adjustment where permitted, but final allowable ampacity can still be limited by lower-temperature terminations or other Code requirements.
Calculation basis and limitations
This tool is structured around NEC Article 310 conductor ampacity workflow. UL standards such as UL 83 and UL 44 define product requirements for thermoplastic- and thermoset-insulated wire; they are not the primary ampacity-sizing code.
Important: voltage-drop limits are design recommendations unless a specific NEC rule or project requirement makes them mandatory. The calculator is a calculation aid and does not determine conductor insulation type, terminal temperature rating, conductor-count exceptions, neutral treatment, parallel-conductor rules, special occupancies, rooftop correction, raceway fill, grounding conductor size, motor-specific conductor rules or every Article-specific requirement. Verify the adopted NEC edition, conductor type, terminal ratings, OCPD rules and application-specific Articles before release.