Printable wire ampacity derating chart

How far to derate copper for hot rooms and full conduits: temperature factors, conductor-count factors and the derated amps for every size from 14 AWG to 500 kcmil. One sheet, fits A4 and US Letter.

Download Excel (.xlsx) Print, or choose “Save as PDF” in the print dialog. The Excel file has every table as its own sortable tab.

Wire ampacity derating

Ambient correction · more than 3 conductors · derated copper by AWG

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Ambient temperature correction — factor by insulation rating

°C	°F	60 °C	75 °C	90 °C
≤ 10	≤ 50	1.29	1.20	1.15
11–15	52–59	1.22	1.15	1.12
16–20	61–68	1.15	1.11	1.08
21–25	70–77	1.08	1.05	1.04
26–30	79–86	1.00	1.00	1.00
31–35	88–95	0.91	0.94	0.96
36–40	97–104	0.82	0.88	0.91
41–45	106–113	0.71	0.82	0.87
46–50	115–122	0.58	0.75	0.82
51–55	124–131	0.41	0.67	0.76
56–60	133–140	—	0.58	0.71
61–65	142–149	—	0.47	0.65
66–70	151–158	—	0.33	0.58
71–75	160–167	—	—	0.50
76–80	169–176	—	—	0.41
81–85	178–185	—	—	0.29
86–90	187–194	—	—	—

Adjustment for more than three current-carrying conductors

Conductors	Multiply by
4–6	80%
7–9	70%
10–20	50%
21–30	45%
31–40	40%
41 and up	35%

Count every current-carrying conductor in the raceway or cable. The neutral of a balanced 3-phase wye circuit usually does not count; the equipment ground never does.

Derated copper ampacity, A — 90 °C wire on 75 °C terminals, 30 °C ambient

AWG	1–3	4–6	7–9	10–20	4–6 at 40 °C
14	20	20	17	12	18
12	25	24	21	15	21
10	35	32	28	20	29
8	50	44	38	27	40
6	65	60	52	37	54
4	85	76	66	47	69
3	100	92	80	57	83
2	115	104	91	65	94
1	130	116	101	72	105
1/0	150	136	119	85	123
2/0	175	156	136	97	141
3/0	200	180	157	112	163
4/0	230	208	182	130	189
250k	255	232	203	145	211
300k	285	256	224	160	232
350k	310	280	245	175	254
400k	335	304	266	190	276
500k	380	344	301	215	313

Start from the 90 °C value, multiply by both factors, then use the smaller of that and the 75 °C value. Example: six 10 AWG at 40 °C = 40 × 0.80 × 0.91 = 29 A. Last column = 4–6 conductors in 40 °C air (× 0.80 × 0.91).

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