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NEC Table 310.16

Complete Conductor Ampacities Reference (2023 Edition)

Standard

NFPA 70

Article

310.16

Temperature Range

60°C - 90°C

Critical Code Requirements

This table is based on not more than three current-carrying conductors in raceway, cable, or earth (directly buried), based on an ambient temperature of 30°C (86°F). Adjustments required for different conditions.

Complete Ampacity Table - Copper & Aluminum

AWG/kcmil	Copper			Aluminum/Copper-Clad
AWG/kcmil	60°C	75°C	90°C	60°C	75°C	90°C
14	15	20	25	—	—	—
12	20	25	30	15	20	25
10	30	35	40	25	30	35
8	40	50	55	35	40	45
6	55	65	75	40	50	55
4	70	85	95	55	65	75
3	85	100	115	65	75	85
2	95	115	130	75	90	100
1	110	130	145	85	100	115
1/0	125	150	170	100	120	135
2/0	145	175	195	115	135	150
3/0	165	200	225	130	155	175
4/0	195	230	260	150	180	205
250 kcmil	215	255	290	170	205	230
300 kcmil	240	285	320	195	230	260
350 kcmil	260	310	350	210	250	280
400 kcmil	280	335	380	225	270	305
500 kcmil	320	380	430	260	310	350
600 kcmil	350	420	475	285	340	385
750 kcmil	400	475	535	320	385	435
1000 kcmil	455	545	615	375	445	500

Note: 75°C column (highlighted) is most commonly used for residential and commercial applications. Terminations typically rated at 75°C per NEC 110.14(C).

Temperature Correction Factors

Ambient Temperature	60°C	75°C	90°C
10°C or less	1.29	1.2	1.15
11-15°C	1.22	1.15	1.12
16-20°C	1.15	1.11	1.08
21-25°C	1.08	1.05	1.04
26-30°C(Standard)	1	1	1
31-35°C	0.91	0.94	0.96
36-40°C	0.82	0.88	0.91
41-45°C	0.71	0.82	0.87
46-50°C	0.58	0.75	0.82
51-55°C	0.41	0.67	0.76
56-60°C	—	0.58	0.71

Example: #12 AWG copper at 75°C = 25A. In 40°C ambient: 25A × 0.88 = 22A adjusted ampacity

Conductor Bundle Adjustment Factors

Current-Carrying Conductors

Number of Conductors	Adjustment Factor
1-3	1.00
4-6	0.8
7-9	0.7
10-20	0.5
21-30	0.45
31-40	0.4
41+	0.35

Calculation Example

Scenario: Six #10 AWG THHN copper conductors in conduit

1. Base ampacity (75°C): 35A
2. Bundle factor (6 conductors): 0.80
3. Adjusted ampacity: 35A × 0.80 = 28A

Neutral conductors carrying only unbalanced load are not counted

Common Circuit Applications

Circuit Type	Copper Wire	Aluminum Wire	Temp Rating	Common Uses
15A General Purpose	14 AWG	12 AWG	60°C	Lighting, receptacles
20A Kitchen/Bath	12 AWG	10 AWG	60°C	Small appliances, bathroom
30A Dryer	10 AWG	8 AWG	75°C	Electric dryer, window AC
40A Range	8 AWG	6 AWG	75°C	Electric range, cooktop
50A Hot Tub	6 AWG	4 AWG	75°C	Spa, EV charger
100A Subpanel	3 AWG	1 AWG	75°C	Garage, workshop
200A Service	3/0 AWG	4/0 AWG	75°C	Main service entrance

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Important Notes & Exceptions

Terminal Temperature Limitations

Conductors with 90°C insulation can use 90°C ampacity only if terminations are rated 90°C
Most residential/commercial equipment has 75°C terminations
Circuits 100A or less: assume 60°C unless marked otherwise
Circuits over 100A: may use 75°C if equipment is rated

When NOT to Use This Table

Conductors in free air (use Table 310.17)
Bare or covered conductors (use Table 310.21)
Underground installations with specific conditions
Motor circuits (see Article 430 for special requirements)

Authority References & Standards

NFPA 70

National Electrical Code

Electrical Applications

Download NEC Table 310.16 PDF

Get a printable reference for field use

How to Read and Apply NEC Table 310.16 — End-to-End

Looking up a number in 310.16 is the easy part. Translating that number into a code-compliant conductor selection requires understanding which column to use, which derating factors apply, and how the table interacts with NEC 240.4(D), NEC 110.14(C), NEC 310.15(B)(1) ambient correction, and NEC 310.15(C)(1) bundling adjustment. This section walks through the full procedure with worked numbers.

Anatomy of NEC Table 310.16 — six columns, one row per AWG

The table organizes ampacities by conductor material (copper or aluminum) and insulation temperature class (60°C, 75°C, or 90°C). The 90°C column is the highest ampacity but is rarely the operative number — most equipment is rated for terminations at 75°C maximum.

Decision tree to pick the column:

What is the LOWEST temperature rating in the circuit? (Conductor, breaker terminals, panel lugs, equipment terminals.) Per NEC 110.14(C), that lowest rating is the column you use.
Standard residential breakers (15–100 A frame) are rated 60°C / 75°C: use the 75°C column for circuits 100 A and below per 110.14(C)(1)(a).
Standard breakers above 100 A frame are rated 75°C only: use the 75°C column.
The 90°C column is used only as a starting point for derating calculations, never as the final ampacity unless every termination is rated 90°C (rare; UL listed industrial equipment).

Worked example — 8 AWG THHN in a 105°F attic with 6 conductors in conduit

Scenario: 60 A continuous load (an EV charger). Run is 8 AWG THHN copper through 1″ EMT in a hot attic. Ambient peaks at 105°F = 41°C. Six total current-carrying conductors in the same conduit (two parallel 3-conductor cable runs, neutral counted as current-carrying because the load is non-linear, e.g., switch-mode EV charger).

Step 1 — Continuous-load 125% (NEC 210.19):

1.25 × 60 A = 75 A required circuit ampacity

Step 2 — Look up base ampacity in 90°C column for derating start:

8 AWG THHN copper @ 90°C = 55 A (per NEC 310.16)

Step 3 — Ambient-temperature correction (310.15(B)(1) at 41°C ambient, 90°C column):

factor = 0.87 → 55 × 0.87 = 47.85 A

Step 4 — Conductor-bundling adjustment (310.15(C)(1) for 6 CCCs):

factor = 0.80 → 47.85 × 0.80 = 38.3 A adjusted ampacity

Step 5 — Compare to required (75 A):

38.3 A < 75 A → 8 AWG IS NOT ADEQUATE

Step 6 — Try 6 AWG THHN @ 90°C = 75 A:

75 × 0.87 × 0.80 = 52.2 A — still inadequate

Step 7 — Try 4 AWG THHN @ 90°C = 95 A:

95 × 0.87 × 0.80 = 66.1 A — still under 75 A

Step 8 — Try 3 AWG THHN @ 90°C = 115 A:

115 × 0.87 × 0.80 = 80.0 A ≥ 75 A ✓

Step 9 — Cap at 75°C termination column (NEC 110.14(C)):

3 AWG @ 75°C = 100 A (above derated 80 A — termination is not the limit here)

Final answer: 3 AWG THHN copper, 60 A breaker, 4 AWG NEC 250.122 EGC

Without derating, you might naively pick 6 AWG (rated 65 A at 75°C, > 60 A load with 125 % factor). The combined hot-attic + bundled-conductor derate eats into ampacity so fast that you have to upsize two AWG steps. This is why every NEC-compliant calculator must check ambient and bundling — picking from the table alone routinely undersizes hot-attic runs.

NEC 310.15(B)(7) — engineering supervision exception

Industrial occupancies under engineering supervision can replace the tabular ampacity values with calculations from the Neher-McGrath equation (NEC 310.15(B)(7)). This produces higher ampacities for buried conductors with favorable thermal conditions but requires a registered professional engineer’s stamp on the calculation.

Neher-McGrath form: I² = (T_c − T_a − ΔT_d) / (R_dc × (1 + Y_c) × R⊂CA⊂)

where:

T_c = max conductor temp, T_a = ambient, ΔT_d = dielectric loss heating

R_dc = DC resistance, Y_c = AC/DC resistance ratio (skin + proximity effects)

R⊂CA⊂ = thermal resistance of insulation, jacket, and surrounding earth

For most field work, the tabular values in NEC 310.16 are conservative and adequate. The Neher-McGrath exception comes up almost exclusively in utility duct-bank design and large data-center power distribution.

Five common 310.16 mistakes

Reading the wrong column. Pulling 8 AWG copper at 55 A (90°C column) for a 50 A circuit when the breaker terminals are rated 75°C and the actual ampacity is 50 A. NEC 110.14(C) caps at the lowest termination temperature.
Forgetting NEC 240.4(D). 12 AWG’s 75°C ampacity is 25 A but the maximum OCPD is 20 A. The conductor can carry 25 A, but you can’t install a 25 A breaker on it.
Skipping NEC 334.80 for NM-B (Romex). NM-B cable conductors are 90°C insulated but NEC 334.80 explicitly requires the 60°C ampacity column for sizing. 12 AWG NM-B has 20 A ampacity, not 25 A.
Cumulative derating in the wrong order. 90°C ampacity × ambient factor × bundling factor → then compare to 75°C termination cap. Some practitioners skip the 90°C starting point and derate from the 75°C value, which under-utilizes high-temperature insulation.
Counting neutrals incorrectly. A balanced 3-phase wye circuit’s neutral is NOT current-carrying for derating purposes (NEC 310.15(B)(5)). But on a 3-phase circuit with a major non-linear (harmonic) load, the neutral DOES count due to triplen harmonic current. Get this wrong and you over-derate or under-derate.

NEC 310.16 only sets ampacity — overcurrent protection is a separate calculation

The output of NEC 310.16 (after all derating) is the maximum continuous current the conductor can carry. It is NOT the breaker size. To pick the breaker:

NEC 240.4(D) — small-conductor rule caps OCPD at 15/20/30 A for 14/12/10 AWG copper.
NEC 240.6(A) — standard breaker sizes are 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000.
NEC 240.4(B) — next standard size up is OK if the conductor ampacity falls between standard sizes (the “next-size-up rule”).
NEC 210.19(A) / 215.2(A) — for continuous loads, the OCPD must be at least 125 % of the continuous portion.