Conductor sizes, areas and resistance

What the code requires

Table 8 lists conductor properties for sizes from 18 AWG up to 2000 kcmil: the cross-sectional area in square millimeters and circular mils, the stranding, the overall diameter and area, and the dc resistance.

Some areas from the table: 14 AWG is 4,110 circular mils, 12 AWG is 6,530 circular mils, 10 AWG is 10,380 circular mils, and 6 AWG is 26,240 circular mils with 7 strands. In the first copper resistance column, given in ohms per kilometer, 12 AWG is 6.34 ohms per km solid and 6.50 ohms per km stranded, and 10 AWG solid is 3.984 ohms per km.

The resistance values are based on 75°C. A note gives a formula for other temperatures, using a temperature coefficient of 0.00323 for copper and 0.00330 for aluminum. Another note sets conductivity at 100% IACS for copper and 61% for aluminum, and compact stranding dimensions are in Table 5A instead.

On the job

• The dc resistance values in Table 8 can be used for voltage-drop calculations.
• For conduit fill, the dimensions of bare conductors may be taken from Table 8.

Exceptions that matter

• The listed values hold only for the conditions the table states; coated strands, different stranding or other temperatures change the resistance.

Related sections

• NEC Chapter 9, Table 1: Conduit fill limits
• NEC Chapter 9, Table 5
• NEC Chapter 9, Table 5A
• NEC Chapter 9, Table 9
• NEC 310.15: Derating wire for heat and crowded conduits

Where this comes from

• NFPA: 2026 NEC (A2025) CMP-6 First Draft public input report, reprinting 2023 Chapter 9 Table 8
• NFPA: 2026 NEC (A2025) CMP-8 First Draft public input report, reprinting 2023 Chapter 9 Table 1 and Notes
• Read the official NEC free at NFPA