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)