NEC Ampacity Chart — Reference Tables

The three tables you need to size a conductor: base ampacity, ambient temperature correction and conductor-count adjustment. For a worked answer use the ampacity calculator.

1. Base ampacity

Taken from the allowable ampacity table for insulated conductors, by temperature rating.

copper

Size60°C75°C90°C
1415 A20 A25 A
1220 A25 A30 A
1030 A35 A40 A
840 A50 A55 A
655 A65 A75 A
470 A85 A95 A
385 A100 A115 A
295 A115 A130 A
1110 A130 A145 A
1/0125 A150 A170 A
2/0145 A175 A195 A
3/0165 A200 A225 A
4/0195 A230 A260 A
250215 A255 A290 A
300240 A285 A320 A
350260 A310 A350 A
400280 A335 A380 A
500320 A380 A430 A
600350 A420 A475 A
750400 A475 A535 A
1000455 A545 A615 A

aluminum

Size60°C75°C90°C
1215 A20 A25 A
1025 A30 A35 A
830 A40 A45 A
640 A50 A55 A
455 A65 A75 A
365 A75 A85 A
275 A90 A100 A
185 A100 A115 A
1/0100 A120 A135 A
2/0115 A135 A150 A
3/0130 A155 A175 A
4/0150 A180 A205 A
250170 A205 A230 A
300195 A230 A260 A
350210 A250 A280 A
400225 A270 A305 A
500260 A310 A350 A
600285 A340 A385 A
750320 A385 A435 A
1000375 A445 A500 A

2. Ambient temperature correction

Multiply the base ampacity by the factor for the ambient temperature and the conductor temperature rating.

Ambient range (°C)60°C conductor75°C conductor90°C conductor
31–350.910.940.96
36–400.820.880.91
41–450.710.820.87
46–500.580.750.82
51–550.410.670.76
56–60—0.580.71
61–65—0.470.65
66–70—0.330.58
71–75——0.50
76–80——0.41

3. Conductor-count adjustment

Conductors in racewayFactor
1–31.00
4–60.80
7–90.70
10–200.50
21–300.45
31–400.40
41+0.35

4. Termination limit

The corrected ampacity does not settle it: terminations cap the usable ampacity as well. Circuits of 100 A or less are limited to the 60°C column unless the terminals and conductor are listed for 75°C; above 100 A the 75°C column applies.

Tables pending review against the current NEC edition. Educational use only — verify before construction.