Wire ampacity table and the 60/75 °C terminal rule
Table 310.16 lists how many amps each wire size carries at 60, 75 and 90 °C. Terminals usually set the limit: 60 °C for circuits of 100 A or less unless the equipment is listed and identified for higher, and 75 °C above 100 A.
What the code requires
Table 310.16 gives ampacities for insulated conductors rated up to 2000 V in raceway, cable or direct burial, assuming 30 °C (86 °F) ambient and no more than 3 current-carrying conductors. Each size has columns for 60, 75 and 90 °C insulation. Sizes marked in the table are also subject to the overcurrent limits in 240.4(D).
Copper, amps at 60/75/90 °C: 14 AWG, 15/20/25; 12 AWG, 20/25/30; 10 AWG, 30/35/40; 8 AWG, 40/50/55; 6 AWG, 55/65/75; 4 AWG, 70/85/95; 3 AWG, 85/100/115; 2 AWG, 95/115/130; 1 AWG, 110/130/145; 1/0, 125/150/170; 2/0, 145/175/195; 3/0, 165/200/225; 4/0, 195/230/260; 250 kcmil, 215/255/290; 350 kcmil, 260/310/350; 500 kcmil, 320/380/430.
Aluminum or copper-clad aluminum, amps at 60/75/90 °C: 12 AWG, 15/20/25; 10 AWG, 25/30/35; 8 AWG, 35/40/45; 6 AWG, 40/50/55; 4 AWG, 55/65/75; 2 AWG, 75/90/100; 1/0, 100/120/135; 2/0, 115/135/150; 3/0, 130/155/175; 4/0, 150/180/205; 250 kcmil, 170/205/230.
Under 110.14(C), equipment for circuits of 100 A or less, or marked for 14 through 1 AWG, is limited to the 60 °C ampacity unless the equipment is listed and identified for higher. Motors marked design B, C or D may use 75 °C. Above 100 A, or for conductors larger than 1 AWG, the 75 °C ampacity applies unless the equipment is listed and identified for a higher-rated conductor. Separate pressure connectors are limited to their listed and identified rating.
On the job
- 6 AWG copper THHN is good for 65 A only where every termination on the circuit is rated 75 °C. Where the default 60 °C termination limit applies, it is good for only 55 A.
- Sizing a circuit from the 90 °C column at the breaker is a common correction.
Exceptions that matter
- Equipment that is listed and identified for higher-temperature conductors may use the higher column.
Related sections
- NEC 110.14(C)
- NEC 240.4(D): Breaker limits for small wires: 14, 12 and 10 AWG
- NEC 310.12: Sizing service wires for a house: the 83% rule
- NEC 310.15: Derating wire for heat and crowded conduits
- NEC 334.80: NM cable ampacity and bundling
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