Conductor Properties

NEC 2020 • 2023 • 2026 COMPLIANT

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Resistance and reactance values for voltage drop math and stranded conductor areas.

Size (AWG/kcmil)	Area (Circ. Mils)	Diameter (in) [Class B]	Copper Res (Ohms/kFT)	Alum Res (Ohms/kFT)
14	4,110	0.073	3.07	5.04
12	6,530	0.092	1.93	3.17
10	10,380	0.116	1.21	1.99
8	16,510	0.146	0.778	1.28
6	26,240	0.184	0.491	0.808
4	41,740	0.232	0.308	0.508
2	66,360	0.292	0.194	0.319
1/0	105,600	0.372	0.122	0.201
2/0	133,100	0.418	0.0967	0.159
3/0	167,800	0.470	0.0766	0.126
4/0	211,600	0.528	0.0608	0.100
250	250,000	0.641	0.0515	0.0847
300	300,000	0.695	0.0435	0.0715
350	350,000	0.744	0.0378	0.0620
400	400,000	0.789	0.0336	0.0551
500	500,000	0.893	0.0276	0.0453
600	600,000	0.964	0.0223	0.0366
700	700,000	0.986	0.0189	0.0310
750	750,000	0.998	0.0176	0.0289
800	800,000	1.029	0.0166	0.0272
900	900,000	1.090	0.0147	0.0241
1000	1,000,000	1.152	0.0132	0.0216
1250	1,250,000	1.289	0.0106	0.0174
1500	1,500,000	1.412	0.00883	0.0145
1750	1,750,000	1.526	0.00756	0.0124
2000	2,000,000	1.632	0.00662	0.0108

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Professional Usage Disclaimer

This data is provided for informational purposes only. Always verify with the latest edition of the National Electrical Code (NFPA 70) and consult with a licensed electrical professional or AHJ (Authority Having Jurisdiction) before performing any electrical work. Zing² is a reference tool, not a substitute for qualified engineering.

Professional Field Notes & Gotchas

▸Voltage Drop Baseline: The DC resistance values at 75°C are the standard variables used in the 'K' Factor voltage drop formula (K = 12.9 for Copper).
▸Stranding Matters: This table assumes Class B stranding. If you are using highly flexible fine-stranded cable (Class K/M), the diameter will be larger and the resistance per foot may vary slightly.
▸Alternating Current (AC): For large conductors (over 4/0), 'Skin Effect' and 'Proximity Effect' increase the effective resistance. For AC math, use Chapter 9, Table 9 instead.
▸Reactance (X): Don't forget that for long AC runs in steel conduit, reactance contributes to voltage drop as much as resistance does. Table 9 captures the combined Impedance (Z).

NEC 2023 vs 2026: What changed?

NEC 2023 vs 2026: No updates to the core resistance or circular mil data. The 2026 code added Informational Notes to Table 8 clarifying 'Uncoated' vs 'Tinned' copper resistance variations in industrial environments.

Technical FAQs

What is the resistance of 1/0 Copper?

Per NEC Chapter 9 Table 8, 1/0 AWG Uncoated Striped Copper has a DC resistance of 0.122 Ohms per 1,000 feet.

How many circular mils in 4/0 wire?

A 4/0 AWG conductor has exactly 211,600 Circular Mils (CM). This value is critical for sizing bonding jumpers under the 12.5% rule.

What is DC resistance vs AC impedance?

DC resistance is constant heat loss. AC impedance (Z) includes both resistance and reactance caused by magnetic fields, which increases in metal pipes and with larger wire sizes.