CalcSpec

NEC Table 310.16 — Wire Ampacity

The most-used ampacity table in North American electrical work — allowable current for insulated conductors up to 2000 V, with three or fewer current-carrying conductors, at 30 °C ambient. Here are the 2023 NEC values plus ambient and conductor-count derating.

Edition
2023NFPA 70
Base ambient
30°C / 86 °F
CCCs assumed
≤ 3in raceway
Voltage
0–2000V
Terminal-temperature rule (110.14(C)) Use the lowest of (a) conductor insulation rating, (b) terminal/lug rating, (c) equipment rating. Most equipment ≤ 100 A or ≤ 1 AWG is listed for 60 °C; most above that is 75 °C. The 90 °C column is almost never the final ampacity — it's used for derating math, then the result is compared back against the 60 / 75 °C terminal column.

Copper Conductors — 2023 NEC Table 310.16

Size
(AWG / kcmil)		 60 °C
(TW, UF)		 75 °C
(THW, THWN, XHHW, USE)		 90 °C
(THHN, THWN-2, XHHW-2, USE-2)
18——14
16——18
1415*20*25*
1220*25*30*
1030*35*40*
8405055
6556575
4708595
385100115
295115130
1110130145
1/0125150170
2/0145175195
3/0165200225
4/0195230260
250215255290
300240285320
350260310350
400280335380
500320380430
600350420475
700385460520
750400475535
800410490555
900435520585
1000455545615
1250495590665
1500525625705
1750545650735
2000555665750

*Small-conductor OCPD cap per 240.4(D): 14 AWG Cu → 15 A, 12 AWG Cu → 20 A, 10 AWG Cu → 30 A, regardless of insulation column.

Aluminum & Copper-Clad Aluminum — Table 310.16

Size (AWG / kcmil) 60 °C 75 °C 90 °C
1215*20*25*
1025*30*35*
8354045
6405055
4556575
3657585
27590100
185100115
1/0100120135
2/0115135150
3/0130155175
4/0150180205
250170205230
300195230260
350210250280
400225270305
500260310350
600285340385
700315375425
750320385435
800330395445
900355425480
1000375445500
1250405485545
1500435520585
1750455545615
2000470560630

*240.4(D) cap applies. Aluminum is not listed for 18, 16, or 14 AWG.

Ambient Correction — NEC 310.15(B)(1)(1)

Multiply the Table 310.16 ampacity by the factor below when the ambient differs from 30 °C.

Ambient °C°F60 °C col.75 °C col.90 °C col.
≤ 10≤ 501.291.201.15
11–1551–591.221.151.12
16–2060–681.151.111.08
21–2569–771.081.051.04
26–3078–861.001.001.00
31–3587–950.910.940.96
36–4096–1040.820.880.91
41–45105–1130.710.820.87
46–50114–1220.580.750.82
51–55123–1310.410.670.76
56–60132–140—0.580.71
61–70141–158—0.33–0.470.58–0.65
71–80159–176——0.41–0.50

Conductor-Count Adjustment — NEC 310.15(C)(1)

Current-carrying conductorsAmpacity multiplier
4 – 680%
7 – 970%
10 – 2050%
21 – 3045%
31 – 4040%
41 and above35%

Neutrals carrying only unbalanced current are generally not counted (310.15(E)); grounding conductors never count.

Worked Example — 12 AWG THHN, 6 CCCs, 35 °C, 75 °C Lugs

  1. Start at the 90 °C column (derating always starts at the conductor's insulation rating): 12 AWG Cu @ 90 °C = 30 A.
  2. Ambient correction (31–35 °C, 90 °C col.): 30 × 0.96 = 28.8 A.
  3. Count adjustment (6 CCCs): 28.8 × 0.80 = 23.0 A.
  4. Terminal limit (110.14(C), 75 °C): 12 AWG Cu @ 75 °C = 25 A. Our 23.0 A is already lower — 23 A governs.
  5. OCPD cap (240.4(D)): 12 AWG Cu capped at 20 A breaker. Compliant — a 20 A breaker protecting 23 A of capacity is fine.
Common mistake Starting the derating from the 75 °C column instead of 90 °C gives 25 × 0.96 × 0.80 = 19.2 A and forces a 15 A breaker. Derating starts at the conductor's insulation column; the final number is then compared to the terminal column — not the other way around.

Edition & Usage Notes

Sources

NFPA NFPA 70 — National Electrical Code OSHA 29 CFR 1910.304 (adopts NEC) ICC Digital Codes — NEC 310.16 Cerrowire Ampacity Charts

FAQ

What is the ampacity of 6 AWG copper wire in NEC Table 310.16?

Per 2023 NEC Table 310.16, a 6 AWG copper conductor is rated 55 A in the 60 C column (TW, UF), 65 A at 75 C (THW, THWN, XHHW), and 75 A at 90 C (THHN, THWN-2, XHHW-2). Values assume 30 C ambient and no more than three current-carrying conductors.

Which insulation column do you use to start conductor derating under the NEC?

Derating always starts at the conductor's insulation rating column, then the result is compared back to the terminal column per 110.14(C). Example from NEC Table 310.16: 12 AWG THHN copper starts at 90 C = 30 A, not the 75 C value of 25 A. Starting at 75 C is a common mistake.

What ambient correction factor applies at 40 C for a 75 C rated conductor?

Per NEC 310.15(B)(1)(1), for ambient 36-40 C (96-104 F), multiply the Table 310.16 ampacity by 0.88 for the 75 C column. The 60 C column factor is 0.82 and the 90 C column factor is 0.91. The base ambient of 30 C uses a factor of 1.00.

What is the ampacity derate for 6 current-carrying conductors in a raceway?

Per NEC 310.15(C)(1), 4-6 current-carrying conductors are derated to 80% of Table 310.16 ampacity. The multiplier drops to 70% for 7-9 conductors, 50% for 10-20, 45% for 21-30, 40% for 31-40, and 35% for 41 and above. Grounding conductors never count.

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Related

NEC ampacity values are facts (not copyrightable) reproduced from NFPA 70 and public manufacturer references. Column-header insulation- type lists are paraphrased. For legally binding work always verify against the edition of NFPA 70 adopted by your AHJ. This page is reference only — not a substitute for a licensed electrician's plan review.