Table B.310.5 Ampacities of Single Insulated Conductors, Rated 0 through 2000 Volts, in Nonmagnetic Underground Electrical Ducts (One Conductor per Electrical Duct), Based on Ambient Earth Temperature of 20°C (68°F), Electrical Duct Arrangement per Figure B.310.2, Conductor Temperature 75°C (167°F)
| Size (kcmil) | 3 Electrical Ducts (Fig. B.310.2, Detail 2) | 6 Electrical Ducts (Fig. B.310.2, Detail 3) | 9 Electrical Ducts (Fig. B.310.2, Detail 4) | Size (kcmil) | ||||||
| Types RHW, THHW, THW, THWN, XHHW, USE | Types RHW, THHW, THW, THWN, XHHW, USE | Types RHW, THHW, THW, THWN, XHHW, USE | ||||||||
| COPPER | ||||||||||
| RHO 60 LF 50 | RHO 90 LF 100 | RHO 120 LF 100 | RHO 60 LF 50 | RHO 90 LF 100 | RHO 120 LF 100 | RHO 60 LF 50 | RHO 90 LF 100 | RHO 120 LF 100 | ||
| 250 | 410 | 344 | 327 | 386 | 295 | 275 | 369 | 270 | 252 | 250 |
| 350 | 503 | 418 | 396 | 472 | 355 | 330 | 446 | 322 | 299 | 350 |
| 500 | 624 | 511 | 484 | 583 | 431 | 400 | 545 | 387 | 360 | 500 |
| 750 | 794 | 640 | 603 | 736 | 534 | 494 | 674 | 469 | 434 | 750 |
| 1000 | 936 | 745 | 700 | 864 | 617 | 570 | 776 | 533 | 493 | 1000 |
| 1250 | 1055 | 832 | 781 | 970 | 686 | 632 | 854 | 581 | 536 | 1250 |
| 1500 | 1160 | 907 | 849 | 1063 | 744 | 685 | 918 | 619 | 571 | 1500 |
| 1750 | 1250 | 970 | 907 | 1142 | 793 | 729 | 975 | 651 | 599 | 1750 |
| 2000 | 1332 | 1027 | 959 | 1213 | 836 | 768 | 1030 | 683 | 628 | 2000 |
| Ambient Temp. (°C) | Correction Factors | Ambient Temp. (°F) | ||||||||
| 6-10 | 1.09 | 1.09 | 1.09 | 43-50 | ||||||
| 11-15 | 1.04 | 1.04 | >1.04 | 52-59 | ||||||
| 16-20 | 1.00 | 1.00 | 1.00 | 61-68 | ||||||
| 21-25 | 0.95 | 0.95 | 0.95 | 70-77 | ||||||
| 26-30 | 0.90 | 0.90 | 0.90 | 79-86 | ||||||
Table B.310.6 Ampacities of Three Insulated Conductors, Rated 0 through 2000 Volts, Within an Overall Covering (Three-Conductor Cable) in Underground Electrical Ducts (One Cable per Electrical Duct) Based on Ambient Earth Temperature of 20°C (68°F), Electrical Duct Arrangement per Figure B.310.2, Conductor Temperature 75°C (167°F)
| Size AWG or (kcmil) | 1 Electrical Ducts (Fig. B.310.2, Detail 1) | 3 Electrical Ducts (Fig. B.310.2, Detail 2) | 6 Electrical Ducts (Fig. B.310.2, Detail 3) | Size AWG or (kcmil) | ||||||
| Types RHW, THHW, THW, THWN, XHHW, USE | Types RHW, THHW, THW, THWN, XHHW, USE | Types RHW, THHW, THW, THWN, XHHW, USE | ||||||||
| COPPER | ||||||||||
| RHO 60 LF 50 | RHO 90 LF 100 | RHO 120 LF 100 | RHO 60 LF 50 | RHO 90 LF 100 | RHO 120 LF 100 | RHO 60 LF 50 | RHO 90 LF 100 | RHO 120 LF 100 | ||
| 8 | 58 | 54 | 53 | 56 | 48 | 46 | 53 | 42 | 39 | 8 |
| 6 | 77 | 71 | 69 | 74 | 63 | 60 | 70 | 54 | 51 | 6 |
| 4 | 101 | 93 | 91 | 96 | 81 | 77 | 91 | 69 | 65 | 4 |
| 2 | 132 | 121 | 118 | 126 | 105 | 100 | 119 | 89 | 83 | 2 |
| 1 | 154 | 140 | 136 | 146 | 121 | 114 | 137 | 102 | 95 | 1 |
| 1/0 | 177 | 160 | 156 | 168 | 137 | 130 | 157 | 116 | 107 | 1/0 |
| 2/0 | 203 | 183 | 178 | 192 | 156 | 147 | 179 | 131 | 121 | 2/0 |
| 3/0 | 233 | 210 | 204 | 221 | 178 | 158 | 205 | 148 | 137 | 3/0 |
| 4/0 | 268 | 240 | 232 | 253 | 202 | 190 | 234 | 168 | 155 | 4/0 |
| 250 | 297 | 265 | 256 | 280 | 222 | 209 | 258 | 184 | 169 | 250 |
| 350 | 363 | 321 | 310 | 340 | 267 | 250 | 312 | 219 | 202 | 350 |
| 500 | 444 | 389 | 375 | 414 | 320 | 299 | 377 | 261 | 240 | 500 |
| 750 | 552 | 478 | 459 | 511 | 388 | 362 | 462 | 314 | 288 | 750 |
| 1000 | 628 | 539 | 518 | 579 | 435 | 405 | 522 | 351 | 321 | 1000 |
| Ambient Temp. (°C) | Correction Factors | Ambient Temp. (°F) | ||||||||
| 6-10 | 1.09 | 1.09 | 1.09 | 43-50 | ||||||
| 11-15 | 1.04 | 1.04 | 1.04 | 52-59 | ||||||
| 16-20 | 1.00 | 1.00 | 1.00 | 61-68 | ||||||
| 21-25 | 0.95 | 0.95 | 0.95 | 70-77 | ||||||
| 26-30 | 0.90 | 0.90 | 0.90 | 79-86 | ||||||