NEC Wire Ampacity Tables — THHN, THWN, Copper & Aluminum Reference

⚡ NEC Wire Ampacity Tables

NEC Table 310.16 — allowable ampacities for insulated conductors rated up to 2000V in raceway, cable, or earth. Copper and aluminum. Includes temperature correction and conduit fill derating factors.

Copper — THHN / THWN-2 (90°C)

NEC Table 310.16 — 75°C column used for terminations per NEC 110.14(C)

Copper

AWG / kcmil	Area (in²)	60°C Amps	75°C Amps	90°C Amps	Common Use
#14 AWG	0.0097	15	20	25	Lighting, general circuits
#12 AWG	0.0133	20	25	30	20A circuits, receptacles
#10 AWG	0.0211	30	35	40	30A circuits, dryers, EV
#8 AWG	0.0366	40	50	55	40-50A circuits, ranges
#6 AWG	0.0507	55	65	75	60A sub-panels, AC
#4 AWG	0.0824	70	85	95	100A feeders
#3 AWG	0.0973	85	100	110	100A service
#2 AWG	0.1158	95	115	130	100-125A service
#1 AWG	0.1562	110	130	150	150A feeders
#1/0 AWG	0.1855	125	150	170	150-200A service
#2/0 AWG	0.2223	145	175	195	200A service
#3/0 AWG	0.2679	165	200	225	200A service entrance
#4/0 AWG	0.3237	195	230	260	200-400A service
250 kcmil	0.3970	215	255	290	Large feeders
300 kcmil	0.4608	240	285	320	Large feeders
350 kcmil	0.5242	260	310	350	400A service
400 kcmil	0.5917	280	335	380	Large commercial
500 kcmil	0.7073	320	380	430	Large commercial service

75°C column is the one you use
Even though THHN is rated 90°C, NEC 110.14(C) limits you to the 75°C column when terminations (breakers, lugs, connectors) are rated 75°C — which is almost always the case. Use the 75°C column for sizing. Use 90°C only for derating calculations.

Source: NEC Table 310.16 — Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts. Ambient temperature 30°C (86°F). Not more than 3 current-carrying conductors in raceway.

Aluminum — XHHW-2 / THWN-2 (90°C)

NEC Table 310.16 — aluminum and copper-clad aluminum conductors

Aluminum

AWG / kcmil	Area (in²)	60°C Amps	75°C Amps	90°C Amps	Copper Equiv.
#12 AWG	0.0133	15	20	25	#10 Cu
#10 AWG	0.0211	25	30	35	#8 Cu
#8 AWG	0.0366	30	40	45	#6 Cu
#6 AWG	0.0507	40	50	60	#4 Cu
#4 AWG	0.0824	55	65	75	#3 Cu
#3 AWG	0.0973	65	75	85	#2 Cu
#2 AWG	0.1158	75	90	100	#1 Cu
#1 AWG	0.1562	85	100	115	#1/0 Cu
#1/0 AWG	0.1855	100	120	135	#2/0 Cu
#2/0 AWG	0.2223	115	135	150	#3/0 Cu
#3/0 AWG	0.2679	130	155	175	#4/0 Cu
#4/0 AWG	0.3237	150	180	205	250 kcmil Cu
250 kcmil	0.3970	170	205	230	300 kcmil Cu
300 kcmil	0.4608	190	230	255	350 kcmil Cu
350 kcmil	0.5242	210	250	280	400 kcmil Cu
400 kcmil	0.5917	225	270	305	500 kcmil Cu
500 kcmil	0.7073	260	310	350	—

Aluminum wire — use anti-oxidant compound
Aluminum conductors require anti-oxidant compound at all terminations to prevent oxidation and maintain connection integrity. Never use aluminum for branch circuits — feeders and service entrance only. Always use terminals rated for aluminum (marked AL or AL/CU).

Source: NEC Table 310.16. Aluminum and copper-clad aluminum conductors. Ambient temperature 30°C (86°F). Not more than 3 current-carrying conductors in raceway.

Derating Factors

NEC Table 310.15(B) temperature correction and Table 310.15(C)(1) conduit fill

Reference

Conduit Fill — More than 3 Current-Carrying Conductors

4–6 conductors	× 0.80 (80%)
7–9 conductors	× 0.70 (70%)
10–20 conductors	× 0.50 (50%)
21–30 conductors	× 0.45 (45%)
31–40 conductors	× 0.40 (40%)
41+ conductors	× 0.35 (35%)

Temperature Correction — 90°C Conductors (THHN)

21–25°C (70–77°F)	× 1.04
26–30°C (79–86°F)	× 1.00 (baseline)
31–35°C (88–95°F)	× 0.96
36–40°C (97–104°F)	× 0.91
41–45°C (106–113°F)	× 0.87
46–50°C (115–122°F)	× 0.82
51–55°C (124–131°F)	× 0.76
56–60°C (133–140°F)	× 0.71
61–70°C (142–158°F)	× 0.58
71–80°C (160–176°F)	× 0.41

Temperature Correction — 75°C Conductors (THWN)

21–25°C (70–77°F)	× 1.05
26–30°C (79–86°F)	× 1.00 (baseline)
31–35°C (88–95°F)	× 0.94
36–40°C (97–104°F)	× 0.88
41–45°C (106–113°F)	× 0.82
46–50°C (115–122°F)	× 0.75
51–55°C (124–131°F)	× 0.67
56–60°C (133–140°F)	× 0.58

How to Apply Both Derating Factors

Step 1	Find base ampacity from Table 310.16 (90°C column)
Step 2	Multiply by temperature correction factor
Step 3	Multiply by conduit fill factor
Step 4	Result must exceed your load current
Step 5	Final ampacity cannot exceed 75°C column value

Equipment grounding conductors don’t count
Equipment grounding conductors (EGC) do not count as current-carrying conductors for the purpose of conduit fill derating. Neutrals count only if they carry harmonic currents (e.g. in circuits with nonlinear loads like VFDs). For standard circuits, the neutral does not count.

Quick Breaker Size Reference

Minimum wire gauge for common breaker sizes — copper THHN at 75°C

Quick Ref

Breaker Size	Min Copper Wire	Min Aluminum Wire	Voltage Drop Note
15A	#14 AWG	N/A (no Al branch)	Under 50ft — fine. Over 100ft — go to #12
20A	#12 AWG	N/A (no Al branch)	Under 75ft — fine. Over 150ft — go to #10
30A	#10 AWG	#8 AWG Al	Under 100ft — fine. Long runs size up
40A	#8 AWG	#6 AWG Al	Check voltage drop on runs over 75ft
50A	#8 AWG	#6 AWG Al	Check voltage drop on runs over 75ft
60A	#6 AWG	#4 AWG Al	Always check voltage drop
100A	#4 AWG	#2 AWG Al	Always run voltage drop calc
125A	#2 AWG	#1/0 AWG Al	Always run voltage drop calc
150A	#1 AWG	#2/0 AWG Al	Always run voltage drop calc
200A	#3/0 AWG	#4/0 AWG Al	Always run voltage drop calc
400A	350 kcmil	500 kcmil Al	Large commercial — always engineer

Minimum wire sizes based on NEC Table 310.16 at 75°C column. Voltage drop not included — run a separate calculation for runs over 50 feet.

How to Read These Tables

The ampacity values in NEC Table 310.16 assume three conditions: ambient temperature of 30°C (86°F), no more than 3 current-carrying conductors in a raceway, and the conductor type shown. If any of those conditions differ on your job, you must derate.

Which column to use — use the 75°C column for almost all termination work. NEC 110.14(C) limits you to 60°C or 75°C at terminations depending on the equipment rating. Modern breakers and panels are typically rated 75°C, so the 75°C column applies. Use the 90°C column only when calculating derated ampacity starting point.
More than 3 conductors in conduit — apply the conduit fill derating factor from NEC Table 310.15(C)(1). Multiply your base 90°C ampacity by the factor, then confirm the result doesn’t exceed the 75°C column value.
High ambient temperature — apply the temperature correction factor. Attics, boiler rooms, rooftop conduit in summer — these environments push ambient temperature well above 30°C and require derating.
Both derating factors apply — when you have both more than 3 conductors AND high ambient temperature, apply both factors. Multiply the 90°C base ampacity by both correction factors. The result is your corrected ampacity.

Copper vs Aluminum — When to Use Each

Aluminum wire is significantly cheaper than copper for the same ampacity but requires one to two gauge sizes larger. For service entrances and large feeder runs, aluminum is standard practice and cost-effective. For branch circuits, copper is required — aluminum branch wiring in homes has a documented history of connection failures and is not used in modern construction.

Use copper for — branch circuits (15A, 20A, 30A), motor circuits, any circuit where connection integrity is critical, short runs where the cost difference is minimal
Use aluminum for — service entrance conductors, large feeder runs (100A+), sub-panel feeds, anywhere copper cost is significant and proper termination is ensured
Aluminum termination rules — use anti-oxidant compound, terminals rated AL or AL/CU, proper torque per manufacturer spec. Never use aluminum with terminals rated CU only.

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When a table value or calculated derating still disagrees with an inspector or the field, use Wire Ampacity Troubleshooting. Re-run the adjustment chain with the Wire Ampacity & Derating Calculator.