Establishing ampacity ratings is an inexact procedure. These tables should only be used as a starting point when determining ratings for any given situation. Values may be lesser or greater than those provided in the table because of the influence of installation method, environment, some 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 64-660: “The Calculation of the Temperature Rise and Load Capability of Cable Systems” by J.H. Neher and M.H. McGrath. This paper was presented at 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. The information contained therein is still applicable.
The following table is to be used in series to determine a wire’s ampacity in a given application. Reference section 6 for examples of applications of these tables.
Quoted WC 73-2000 (R2005) Page 6 © 2005 National Electrical Manufacturers Association.
Base Ampacities
Allowable ampacities of insulated conductors rated 0 through 2000 Volts, 60° to 90°C (140° 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 | 150°C 3 BC, TCC | 200°C BC, TCC, SCC, or NCC 2% - 10% | 250°C NCC 2% - 10% | 250° "A" Nickel | 450°C NCC- Class 27 | 450°C "A" Nickel |
|---|---|---|---|---|---|---|
| 24 | 6.6 | 72 | 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 |
| 144 | 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 |
65| 96 | 110 | 117 | 55 | 138 | 65 |
|
| 4 | 120 | 125 | 148 | 69 | 1622 | 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 | 144 | 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 |
3 This column is for reference purposes only
4 14-8 AWG 150 – 150 NCC data is from NEC Table 310-18
5 6-4/0 150-250 NCC date is from NEC Table 310-18