Suggested Wire Ampacities

Ampacity, or current carrying capacity, is defined as the current a conductor can carry before its temperature exceeds a permissible value. The correct conductor size ensures that the heat generated by the flow of current through the conductor and the heat of the ambient temperature does not exceed the thermal rating of the insulation.

There are many factors which will limit the amount of current that can be passed through a wire:

CONDUCTOR SIZE: The larger the circular mil area, the greater the current capacity.

INSULATION: The amount of heat generated should never exceed the maximum temperature rating of the insulation.

NUMBER OF CONDUCTORS: Heat dissipation is lessened as the number of individually insulated conductors that are bundled together are increased.

INSTALLATION CONDITIONS: Restricting heat dissipation by installing the conductors in conduit, duct, trays or raceways lessens the current carrying capacity. This restriction can be alleviated by using proper ventilation methods, forced air cooling, etc.

Assigning a current rating to a wire is essentially a heat transfer problem. Without overheating the conductor or insulation, the watts produced at the conductor must be dissipated through the insulation to the ambient.

While organizations like the Insulated Cable Engineers Association and the National Electric Code have formally issued current ratings for power cables, no such ratings have been produced for appliance wires or equipment cables.

It is nearly impossible to standardize actual current ratings since appliance and device designs vary so greatly.

SUGGESTED AMPACITIES (All Types of Single Conductor Insulation)

AWG 80C 90C 105C 125C 150C 200C 250C*
AMPERES PER CONDUCTOR
30 2 3 3 3 3 4 4
28 3 4 4 5 5 6 6
26 4 5 5 6 6 7 8
24 6 7 7 8 8 10 11
22 8 9 10 11 12 13 14
20 10 12 13 14 15 17 19
18 15 16 18 20 22 24 29
16 18 20 24 26 29 32 37
14 20 25 33 40 40 45 39
12 25 30 45 50 50 55 54
10 35 40 58 70 70 75 73

CORRECTION FACTORS FOR VARIOUS AIR TEMPERATURES
30 1.00 1.00 1.00 1.00 1.00 1.00 1.00
40 0.88 0.90 0.92 0.95 0.96 0.97 0.98
50 0.75 0.80 0.82 0.89 0.91 0.93 0.95
60 0.58 0.67 0.73 0.83 0.87 0.91 0.95
70 0.35 0.52 0.61 0.76 0.82 0.87 0.93
80 - 0.30 0.46 0.69 0.76 0.84 0.90
90 - - 0.30 0.61 0.71 0.80 0.87
100 - - - 0.51 0.65 0.77 0.85
125 - - - - 0.50 0.66 0.72
150 - - - - - 0.54 0.65
200 - - - - - - 0.49

This table shows the suggested ampacities for all types of single conductor insulation including amperes per conductor and correction factors for various air temperatures. Current ratings for different conductor materials may be calculated by multiplying the appropriate copper conductor ratings by the following factors:

*NICKEL PLATED COPPER: 0.87
 NICKEL: 0.43

Suggested Current Carrying Capacity Table (Base Temperature at 40C)

150C
Tinned Copper

 200C
Tinned Copper NPC 2% - 10%		 250C
NPC 2% - 10%		 250C
"A" Nickel		 250C
NPI		 450C
NPC - 27%		 450C
"A" Nickel
24 6.6 7.2 8 4 3.3 9 4.3
22 9 9.6 10.8 5 4.4 12 5.6
20 13 14 15 7 6 18 8
18 17 18 20 9.4 8 23 11
16 22 24 26 12 11 30 14
14 34 36 39 18 16 45 21
12 43 45 54 25 22 56 26
10 55 60 73 34 30 75 35
8 76 83 93 43 39 104 49
6 96 110 117 55 49 138 65
4 120 125 148 69 62 162 76
3 143 152 166 78 69 182 85
2 160 171 191 90 80 210 99
1 186 197 215 101 90 236 110
1/0 215 229 244 114 102 268 126
2/0 251 260 273 128 114 300 141
3/0 288 297 308 144 129 338 159
4/0 332 346 361 169 151 397 186
250 365 385 398 187 167 - -
300 414 436 452 212 190 - -
350 461 486 503 236 211 - -
400 495 522 540 254 226 - -
500 563 593 613 288 257 - -

This table shows the suggested current carrying capacities with a base temperature at 40 degrees Celsius.

NOTE: For allowable ampacities for fixture wire, please see the National Electrical Code Handbook.

For ambient temperatures other than 40C (104F), multiply the ampacities shown above by the appropriate factor shown below. 

Wire Temperature Rating

Ambient Temperature (C) 200C 250C 450C Ambient Temperature (F)
41-50 0.97 0.98 0.99 106-122
51-60 0.94 0.95 0.99 124-140
61-70 0.90 0.93 0.96 142-158
71-80 0.87 0.90 0.95 160-176
81-90 0.83 0.87 0.93 177-194
91-100 0.72 0.85 0.92 195-212
101-120 0.71 0.79 0.89 213-248
121-140 0.61 0.71 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

NOTE: The use of this table for establishing ampacity ratings is an inexact procedure. This table should only be used as a starting point when establihsing ratings for any given situations. It is recommended that design engineers desiring accurate ampacity data study the National Electrical Code Handbook - Article 310-13-310-84.

Suggested Ampacities (All Types of Insulations)

COPPER ALUMINUM
Not More Than 3 Conductors in Raceway or Cable Single Conductor in Free Air Not More Than 3 Conductors in Raceway or Cable Single Conductor in Free Air
CONDUCTOR TEMPERATURE RATINGS
AWG or
MCM		 85-90C
Temp
(185F)		 110C
Temp
(230F)		 85-90C
Temp
(185F)		 110C
Temp
(230F)		 125C
Temp
(257F)		 200C
Temp
(392F)		 85-90C
Temp
(185F)		 110C
Temp
(185F)		 85-90C
Temp
(185F)		 110C
Temp
(230F)		 125C
Temp
(257F)		 200C
Temp
(392F)
AMPERES PER CONDUCTOR (100% LOAD FACTOR)
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
00 190 215 290 330 355 370 145 170 220 255 275 290
000 215 245 335 385 410 430 170 195 255 300 320 335
0000 250 275 390 445 475 510 195 215 300 345 390 400
250 275 315 440 495 530 - 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 1,005 - 405 455 645 475 795 -
750 515 580 855 980 1,045 - 420 470 670 775 825 -
800 535 600 885 1,020 1,085 - 430 485 695 805 855 -
900 565 - 950 - - - 465 - 750 - - -
1,000 590 680 1,020 1,165 1,240 - 485 560 800 930 990 -

This table shows the suggested ampacities for all types of insulation including conductor temperature ratings and amperes per conductor.

CORRECTION FACTORS FOR VARIOUS AMBIENT AIR TEMPERATURES

40C 0.90 0.94 0.90 0.94 0.95 - 0.90 0.94 0.90 0.94 0.95 -
50C 0.80 0.87 0.80 0.87 0.89 - 0.80 0.87 0.80 0.87 0.89 -
60C 0.67 0.79 0.67 0.79 0.83 0.91 0.67 0.79 0.67 0.79 0.83 0.91
70C 0.52 0.71 0.52 0.71 0.76 0.87 0.52 0.71 0.52 0.71 0.76 0.87
80C 0.30 0.61 0.30 0.61 0.69 0.84 0.30 0.61 0.30 0.61 0.69 0.84
90C - 0.50 - 0.50 0.61 0.80 - 0.50 - 0.50 0.61 0.80
100C - - - - 0.51 0.77 - - - - 0.51 0.77
120C - - - - - 0.69 - - - - - 0.69
140C - - - - - - 0.59 - - - - 0.59

*Based on an ambient temperature of 30C (86F)

The table above shows the correction factors for various ambient air temperatures anywhere from 40 degrees Celsius to 140 degrees Celsius.

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