NEC Ampacity Data

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Table 310.15(B)(2)(b) Ambient Temperature Correction Factors Based on 40°C (104°F)

For ambient temperatures other than 40°C (104°F), multiply the allowable ampacities specified in the ampacity tables by the appropriate correction factor shown below.


Temperature Rating of Conductor
Ambient Temperature
(°C)
60°C75°C90°C150°C200°C250°CAmbient Temperature (°F)
10 or less1.581.361.261.131.091.0750 or less
11-151.501.311.221.111.081.0651-59
16-201.411.251.181.091.061.0560-68
21-251.321.201.141.071.051.0469-77
26-30 1.22 1.13 1.10 1.04 1.03 1.0278-86
31-351.121.071.051.021.021.0187-95
36-401.001.001.001.001.001.0096-104
41-450.870.930.950.980.980.99105-113
46-500.710.850.890.950.970.98114-122
51-550.500.760.840.930.950.96123-131
56-600.650.770.900.940.95132-140
61-650.530.710.880.920.94141-149
66-700.380.630.850.900.93150-158
71-750.550.830.880.91159-167
76-800.450.800.870.90168-176
81-900.740.830.87177-194
91-1000.670.790.85195-212
101-1100.600.750.82213-230
111-1200.520.710.79231-248
121-1300.430.660.76249-266
131-1400.300.610.72267-284
141-1600.500.65285-320
161-1800.350.58321-356
181-2000.49357-392
201-2250.35393-437

Table 310.15(B)(3)(a) Adjustment Factors for More Than Three Current-Carrying  Conductors in a Raceway or Cable

Number of ConductorsPercent of Values in Table 310.15(B)(16) through Table 310.15(B)(19) as Adjusted for Ambient Temperature if Necessary
4-680
7-970
10-2050
21-3045
31-4040
41 and above35

* Number of conductors  is the total number of conductors  in the race­way or cable  adjusted  in accordance  with 31 0.15(B)(5) and (6).

Informational Note No. 2:   See 366.23(A) for adjustment factors for conductors in sheet metal auxiliary gutters and 376.22(B) for adjustment factors for conductors in metal wireways.

(1) Where conductors  are installed in cable trays, the provisions of 392.80 shall apply.
(2)  Adjustment factors  shall  not apply  to conductors in raceways having a length not exceeding 600  mm (24 in.).
(3) Adjustment factors shall not apply to underground conductors entering or leaving an outdoor trench if those conductors  have  physical  protection in the form of  rigid metal conduit, intermediate metal conduit, rigid polyvinyl chloride conduit (PVC), or reinforced thermosetting resin conduit (RTRC) having a length not exceeding 3.05 m (10 ft), and if the number of conductors does not exceed four.
(4)  Adjustment factors shall not apply to Type AC cable or to Type MC cable under the following  conditions:

  1. The cables do not have an overall outer jacket.
  2. Each cable has not more than three current-carrying conductors.
  3. The conductors are 12 AWG  copper.
  4. Not more than 20 current-carrying conductors are installed without maintaining spacing, are stacked, or are supported on”bridle rings.”

(5)  An adjustment factor of 60 percent shall be applied to Type AC cable or Type MC cable under the following conditions:

  1. The cables do not have an overall outer jacket.
  2. The number of current carrying conductors exceeds 20.
  3. The cables are stacked or bundled longer that 600 mm (24 in) without spacing being maintained.

(b) More Than One Conduit, Tube, or Raceway. Spacing between conduits, tubing, or raceways shall be maintained.
(c)  Circular Raceways Exposed to Sunlight on Roof­tops.  Where conductors or cables are installed in circular raceways exposed to direct sunlight on or above rooftops, the adjustments shown in Table 310.15(B)(3)(c) shall be added to the outdoor temperature to determine the applicable ambient temperature for application of the correction factors in Table 31 0.15(B)(2)(a) or Table 31 0.15(B)(2)(b).

Informational Note:  One source for the average ambient temperatures in various locations is  the ASHRAE Hand­book Fundamentals.

Table 310.15(B)(3)(c)  Ambient Temperature Adjustment for Circular Raceways Exposed to Sunlight on or Above Rooftops

Distance Above Roof to Bottom of ConduitTemperature Adder °CTemperature Adder °F
0-13 mm (½ in.)3360
Above 13 mm (½ in.) –
90 mm (3½ in.)
2240
Above 90 mm (3½ in.) –
300 mm (12 in.)
1730
Above 300 mm (12 in.) –
900 mm (36 in.)
1425

Informational Note to Table 31 0.15(B)(3)(c): The temperature adders in  Table 310.15(B)(3)(c)  are based on the results of averaging the ambient temperatures.

(4)  Bare  or Covered  Conductors. Where bare or covered conductors are installed with insulated conductors, the temperature rating of the bare or covered conductor shall be equal to the lowest temperature rating of the insulated con­ductors for the purpose of determining  ampacity.

(5)   Neutral Conductor.

(a)  A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required  to be counted when applying the provisions of 310.15(B)(3)(a).
(b)  In a 3-wire circuit consisting of two phase conductors and the neutral conductor of a 4-wire, 3-phase, wye-connected system, a common conductor carries approximately the same current as the line-to-neutral load currents of the other conduc­tors and shall be counted when applying the provisions of 310.15(B)(3)(a).
(c) On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic cur­rents are present in the neutral conductor; the neutral conductor shall therefore be considered a current-carrying conductor.

(6)  Grounding or Bonding  Conductor. A grounding or bonding conductor shall not be counted  when applying the provisions of 31 0.15(B)(3)(a).

Table 310.15(B)(16) (formerly  Table 310.16) Allowable Ampacities of Insulated  Conductors  Rated Up to and Including 2000 Volts, 60°C Through 90°C (140°F Through  194°F), Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30°C (86°F)*


Temperature Rating of Conductor
[See Table 310.104(A).]

60°C (140°F)75°C (167°F)90°C (194°F)60°C (140°F)75°C (167°F) 90°C (194°F)
Types TW, UFTypes RHW, THHW,
THW, THWN, XHHW, USE, ZW
Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN,
THHW, THW-2, THWN·2, USE-2, XHH, XHHW,
XHHW-2, ZW-2
Types TW, UFTypes RHW, THHW, THW, THWN, XHHW, USETypes TBS, SA, SIS, THHN, THHW, THW-2, THWN-2,
RHH, RHW-2, USE-2, XHH, XHHW,
XHHW-2, ZW-2
Size AWG
or kcmil
COPPERALUMINUM OR COPPER-CLAD ALUMINUMSize AWG or kcmil
1814
1618
14**152025
12**20253015202512**
10**30354025303510**
84050553540458
65565754050556
47085955565754
3851001156575853
29511513075901002
1110130145851001151
1/01251501701001201351/0
2/01451751951151351502/0
3/01652002251301551753/0
4/01952302601501802054/0
250215255290170205230250
300240285320195230260300
350260310350210250280350
400280335380225270305400
500320380430260310350500
600350420475285340385600
700385460520315375425700
750400475535320385435750
800410490555330395445800
900435520585355425480900
10004555456153754455001000
12504955906654054855451250
15005256257054355205851500
17505456507354555456151750
20005556657504705606302000

*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 30°C (86°F).
**Refer to 240.4(D) for conductor overcurrent protection limitations.

Table 310.15(B)(17) (formerly Table 310.17) Allowable Ampacities of Single-Insulated Conductors Rated Up to and Including 2000 Volts in Free Air, Based on Ambient Temperature of 30°C (86°F)*


Temperature Rating of Conductor
[See Table 310.104(A).]

60°C (140°F)75°C (167°F)90°C (194°F)60°C (140°F)75°C (167°F) 90°C (194°F)
Types TW, UFTypes RHW, THHW, THW, THWN,
XHHW, ZW
Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2,
THHN, THHW, THW-2,
THWN·2, USE-2, XHH,
XHHW, XHHW-2, ZW-2
Types TW, UFTypes RHW, THHW, THW, THWN, XHHWTypes TBS, SA, SIS, THHN, THHW, THW-2, THWN-2,
RHH, RHW-2, USE-2, XHH,
XHHW, XHHW-2,
ZW-2
Size AWG
or kcmil
COPPERALUMINUM OR COPPER-CLAD ALUMINUMSize AWG or kcmil
1818
1624
14**253035
12**303540 25 30 3512**
10**405055 35 40 4510**
8607080 45 55 608
68095105 60 75 856
4105125140 80 100 1154
3120145165 95 115 1303
2140170190 110 135 1502
1165195220 130 155 1751
1/0195230260 150 180 2051/0
2/0225265300 175 210 2352/0
3/0260310350 200 240 2703/0
4/0300360405 235 280 315 4/0
250340405455 265 315 355250
300375445500 290 350 395300
350420505570 330 395 445350
400455545615 355 425 480400
500515620700 405 485 545500
600575690780 455 545 615600
700630755850 500 595 670700
750655785885 515 620 700750
800680815920 535 645 725800
900730870980 580 700 790900
10007809351055 625 750 8451000
125089010651200 710 855 9651250
150098011751325 795 950 10701500
1750107012801445 875 1050 11851750
2000115513851560 960 1150 12952000

*Refer to 310.15(B)(2) for the ampacity correction factors where the ambient temperature is other than 30°C (86°F).
**Refer to 240.4(D) for conductor overcurrent protection limitations.

Table 310.15(B)(20) (formerly  Table 310.20) Ampacities of Not More Than Three Single Insulated Conductors, Rated Up to and Including 2000 Volts, Supported on a Messenger, Based on Ambient Air Temperature of 40°C (104°F)


Temperature Rating of Conductor
[See Table 310.104(A).]

75°C (167°F)90°C (194°F)75°C (167°F)90°C (194°F)
Types RHW, THHW,
THW, THWN, XHHW, ZW
Types MI, THHN, THHW, THW-2, THWN-2, RHH,
RHW-2, USE-2, XHHW,
XHHW-2, ZW-2
Types RHW, THW, THWN, THHW,
XHHW
Types THHN, THHW, RHH, XHHW, RHW-2,
XHHW-2, THW-2,
THWN-2, USE-2, ZW-2
Size AWG or kcmil COPPERALUMINUM OR COPPER-CLAD ALUMINUMSize AWG or kcmil
8576644518
6768959696
410111778914
3118138921073
21351581061232
11581851231441
1/01832141431671/0
2/02122471651932/0
3/02452871922243/0
4/02873352242624/0
250320374251292250
300359419282328300
350397464312364350
400430503339395400
500496580392458500
600553647440514600
700610714488570700
750638747512598750
800660773532622800
900704826572669900
10007488796127161000

*Refer to 310.15(B)(2)  for the ampacity correction factors where the ambient temperature is other than 40°C (104°F).

Table 310.15(B)(21) (formerly  Table 310.21) Ampacities of Bare or Covered Conductors  in Free Air, Based on 40°C (104°F) Ambient, 80°C (176°F) Total Conductor Temperature, 610 mm/sec (2 ft/sec) Wind Velocity

Copper Conductors
AAC Aluminum Conductors
Bare
Covered
Bare
Covered
AWG or kcmilAmperesAWG or kcmilAmperesAWG or kcmilAmperesAWG or kcmilAmperes
8988103876880
612461306966101
4155416341214127
2209221921632171
1/02821/02971/02201/0231
2/03292/03442/02552/0268
3/03823/04013/02973/0312
4/04444/04664/03464/0364
250494250519266.8403266.8423
300556300584336.4468336.4492
500773500812397.5522397.5548
75010007501050477588477617
1000119310001253556.5650556.5682
 – – –636 709636 744
 – – – – 795 819795 860
 – – – – 954 920 – –
 – – – – 1033.5 968 1033.5 1017
1272110312721201
1590126715901381
 2000 1454 2000 1527

Table 310.60(C)(4) Ambient Temperature Correction Factors

For ambient temperatures other than 40°C (104°F), multiply the allowable ampacities  specified in the ampacity  tables by the appropriate factor shown below.

Temperature Rating of Conductor
Ambient Temperature (°C)90°C 105°C Ambient Temperature (°F)
10 or less1.261.2150 or less
11-151.221.1851-59
16-201.181.1460-68
21-251.141.1169-77
26-301.101.0778-86
31-351.051.0487-95
36-401.001.0096-104
41-450.950.96105-113
46-500.890.92114-122
51-550.840.88123-131
56-600.770.83132-140
61-650.710.78141-149
66-700.630.73150-158
71-750.550.68159-167
76-800.450.62168-176
81-850.320.55177-185
86-900.48186-194
91-950.39195-203
96-1000.28204-212

Table 310.60(C)(67) Ampacities of Insulated Single Copper Conductor Cables Triplexed in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*


Temperature Rating of Conductor
[See Table 310.104(C).]
2001-5000 Volts Ampacity 5001-35,000 Volts Ampacity
Conductor Size (AWG or kcmil)90°C (194°F) Type MV-90105°C (221°F) Type MV-10590°C (194°F) Type MV-90105°C (221°F) Type MV-105
86574
69099100110
4120130130140
2160175170195
1185205195225
1/0215240225255
2/0250275260295
3/0290320300340
4/0335375345390
250375415380430
350465515470525
500580645580650
750750835730820
1000880980850950

*Refer to 310.60(C)(4) for the ampacity correction factors where the ambient air temperature  is other than 40°C (104°F).

Table 310.60(C)(68) Ampacities of Insulated Single Aluminum Conductor Cables Triplexed in Air Based on Conductor Temperatures of 90°C  (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C  (104°F)*


Temperature Rating of Conductor
[See Table 310.104(C).]
2001-5000 Volts Ampacity 5001-35,000 Volts Ampacity
Conductor Size (AWG or kcmil)90°C (194°F) Type MV-90105°C (221°F) Type MV-10590°C (194°F) Type MV-90105°C (221°F) Type MV-105
85057
670777584
490100100110
2125135130150
1145160150175
1/0170185175200
2/0195215200230
3/0225250230265
4/0265290270305
250295325300335
350365405370415
500460510460515
750600665590660
1000715800700780

*Refer to 310.60(C)(4) for the ampacity correction  factors where the ambient air temperature  is other than 40°C (104°F).

Table 310.60(C)(69) Ampacities of Insulated Single Copper Conductor Isolated in Air Based on Conductor Temperatures of 90°C (194°F) and 105°C (221°F) and Ambient Air Temperature of 40°C (104°F)*


Temperature Rating of Conductor
[See Table 310.104(C).]
2001-5000 Volts Ampacity 5001-15,000 Volts Ampacity 15,001-35,000 Volts Ampacity
Conductor Size (AWG or kcmil)90°C (194°F) Type MV-90105°C (221°F) Type MV-10590°C (194°F) Type MV-90105°C (221°F) Type MV-10590°C (194°F) Type MV-90105°C (221°F) Type MV-105
88393 – –
6110120110125
4145160150165
2190215195215
1225250225250225250
1/0260290260290260290
2/0300330300335300330
3/0345385345385345380
4/0400445400445395445
250445495445495440490
350550615550610545605
500695775685765680755
7509001000885990870970
1000107512001060118510401160
1250123013701210135011851320
1500136515251345150013151465
1750149516651470164014301595
2000160517901575175515351710

*Refer to 310.60(C)(4)  for the ampacity correction  factors where the ambient air temperature  is other than 40°C (104°F).