Ampacities and Correction Factors

Introduction

Establishing ampacity ratings is an inexact procedure. For any given situation, these tables should only be used as a starting point when establishing ratings. Values may be greater than or less than those given in the tables because of the influence of installation method, environment, number of conductors, conductor composition and size, ambient temperatures, insulation types, etc. It is recommended that design engineers desiring accurate ampacity data closely study the 1999 National Electrical Code, Articles 310-15 through 310-84. Additional information can be derived from AIEE, Paper Number 57-660: "The Calculation of the Temperature Rise and Load Capability of Cable Systems" by J.H. Neher and M. H. McGrath. This paper was presented to the AIEE general meeting in Montreal, Quebec, Canada on June 24-28, 1957, and was published in the "AIEE Transactions," Part 3 (power apparatus and systems), Volume 76, October 1957, pp. 752- 772. That information is still applicable. The following tables are to be used in series to determine a wire's ampacity in a given application. Section 6 should be used as a reference for examples of applications of these tables.

Base Ampacities

ALLOWABLE AMPACITIES OF INSULATED CONDUCTORS RATED - THROUGH 2000 VOLTS, 60°C TO 90°C (140°F TO 194°F) NOT MORE THAN THREE CURRENT-CARRYING CONDUCTORS IN RACEWAY OR CABLE OR EARTH (DIRECTLY BURIED), BASED ON AMBIENT TEMPERATURES OF 40°C (104°F)

AWG	105°C BC, TCC	200°C BC, TCC, SCC, or NCC 2%-10%	250°C NCC 2%-10%	250 °C "A" Nickel	450°C NCC-Class 27	450°C "A" Nickel
24	6.6	7.2	8	4	9	4.3
22	9	9.6	10.8	5	12	5.6
20	13	14	15	7	18	8
18	17	18	20	9.4	23	11
16	22	24	26	12	30	14
14	34	36	39	18	45	21
12	43	45	54	25	56	26
10	55	60	73	34	75	35
8	76	83	93	43	104	49
6	96	110	117	55	138	65
4	120	125	148	69	162	76
3	143	152	166	78	182	85
2	160	171	191	90	210	99
1	186	197	215	101	236	110
1/0	215	229	244	114	268	126
2/0	251	260	273	128	300	141
3/0	288	297	308	166	338	159
4/0	332	346	361	169	397	186
250	365	385	398	187	--	--
300	414	436	452	212	--	--
350	461	486	503	236	--	--
400	495	522	540	254	--	--
500	563	593	613	288	--	--

Temperature Correction Factors

CORRECTION FACTORS FOR AMBIENT TEMPERATURES OTHER THAN 40°C (104°F),
MULTIPLY THE AMPACITIES BY THE APPROPRIATE FACTOR SHOWN BELOW

Ambient Temp °C	105 °C	200 °C	250 °C	450 °C	Ambient Temp °F
41-50	0.95	0.97	0.98	0.99	106-122
51-60	0.90	0.94	0.95	0.99	124-140
61-70	0.85	0.90	0.93	0.96	142-158
71-80	0.80	0.87	0.90	0.95	160-176
81-90	0.74	0.83	0.87	0.93	177-194
91-100	0.67	0.79	0.85	0.92	195-212
101-120	0.52	0.71	0.79	0.89	213-248
121-140	0.30	0.61	0.72	0.86	249-284
141-160	--	0.50	0.65	0.84	285-320
161-180	--	0.35	0.58	0.81	321-356
181-200	--	--	0.49	0.78	357-392
201-225	--	--	0.35	0.74	393-437
226-250	--	--	--	0.69	439-482
251-275	--	--	--	0.65	483-527
276-300	--	--	--	0.60	528-572
301-325	--	--	--	0.55	573-617
326-350	--	--	--	0.49	618-662
351-375	--	--	--	0.42	663-707
376-400	--	--	--	0.34	708-752
401-450	--	--	--	--	753-842

ADJUSTMENT FACTORS FOR MORE THAN THREE CURRENT-CARRYING CONDUCTORS IN A RACEWAY OR CABLE
(NEC Table 310-15 (b)(2)(a))

Number of Current-Carrying Conductors	Percent of Values as Adjusted for Ambient Temperature if Necessary
4-6	80
7-9	70
10-20	50
21-30	45
31-40	40
41 and above	35

Suggested Ampacities and Conversions

All types of insulations - Based on National Electric Code

	Copper						Aluminum
	No more than 3 conductors in raceway or cable			Single conductor in free air			No more than 3 conductors in raceway or cable			Single conductor in free air
	Conductor Temperature Rating						Conductor Temperature Rating
Size AWG or MCM	85-90°C TEMP 185F	110°C TEMP 230F	85-90°C TEMP 185F	110°C TEMP 230F	125°C TEMP 257F	200°C TEMP 392F	85-90°C TEMP 185F	110°C TEMP 230F	85-90°C TEMP 185F	110°C TEMP 230F	125°C TEMP 257F	200°C TEMP 392F
14	25	30	30	40	40	45	--	--	--	--	--	--
12	30	35	40	50	50	55	25	25	30	40	40	45
10	40	45	55	65	70	75	30	35	45	50	55	60
8	55	60	75	85	90	100	40	45	55	65	70	80
6	70	80	100	120	125	135	55	60	80	95	100	105
4	95	105	135	160	170	180	75	80	105	125	135	140
2	125	135	185	210	225	240	100	105	140	165	175	185
1	145	160	215	245	265	280	110	125	165	190	205	220
0	165	190	250	285	305	325	130	150	190	220	240	255
1/0	190	215	290	330	355	370	145	170	220	255	275	290
2/0	215	245	335	385	410	430	170	195	255	300	320	335
3/0	250	275	390	445	475	510	195	220	300	345	370	400
4/0	275	315	440	495	530	--	220	250	330	385	415	--
300	310	345	485	555	590	--	250	275	375	435	460	--
350	340	390	550	610	655	--	270	310	415	475	510	--
400	365	420	595	665	710	--	295	335	450	520	555	--
500	415	470	675	765	815	--	335	380	515	595	635	--
600	460	525	750	855	910	--	370	425	585	675	720	--
700	500	560	825	940	1005	--	405	455	646	745	795	--
750	515	580	855	980	1045	--	420	470	670	775	825	--
800	535	600	885	1020	1085	--	430	485	695	805	855	--
900	565	--	950	--	--	--	465	--	750	--	--	--
1000	590	680	1020	1165	1240	--	485	560	800	930	990	--

Correction Factors for Various Ambient Temperatures*

40°C	0.9	0.94	0.9	0.9	0.95	--	0.9	0.94	0.9	0.94	0.95	--
50°C	0.8	0.87	0.8	0.87	0.89	--	0.8	0.87	0.8	0.87	0.89	--
60°C	0.67	0.79	0.67	0.79	0.83	0.91	0.67	0.79	0.67	0.79	0.83	0.91
70°C	0.52	0.71	0.52	0.71	0.76	0.87	0.52	0.71	0.52	0.71	0.76	0.87
80°C	0.3	0.61	0.3	0.61	0.71	0.84	0.3	0.61	0.3	0.61	0.71	0.84
90°C	--	0.5	--	0.5	0.61	0.81	--	0.5	--	0.5	0.61	0.81
100°C	--	--	--	--	0.51	0.77	--	--	--	--	0.51	0.77
120°C	--	--	--	--	--	0.69	--	--	--	--	--	0.69
140°C	--	--	--	--	--	0.59	--	--	--	--	--	0.59

*Based on ambient temperature of 30°C (85°F)