Table B.310.7 Ampacities of Three Single Insulated Conductors, Rated 0 Through 2000 Volts, in Underground Electrical Ducts (Three Conductors 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 | 63 | 58 | 57 | 61 | 51 | 49 | 57 | 44 | 41 | 8 |
| 6 | 84 | 77 | 75 | 80 | 67 | 63 | 75 | 56 | 53 | 6 |
| 4 | 111 | 100 | 98 | 105 | 86 | 81 | 98 | 73 | 67 | 4 |
| 3 | 129 | 116 | 113 | 122 | 99 | 94 | 113 | 83 | 77 | 3 |
| 2 | 147 | 132 | 128 | 139 | 112 | 106 | 129 | 93 | 86 | 2 |
| 1 | 171 | 153 | 148 | 161 | 128 | 121 | 149 | 106 | 98 | 1 |
| 1/0 | 197 | 175 | 169 | 185 | 146 | 137 | 170 | 121 | 111 | 1/0 |
| 2/0 | 226 | 200 | 193 | 212 | 166 | 156 | 194 | 136 | 126 | 2/0 |
| 3/0 | 260 | 228 | 220 | 243 | 189 | 177 | 222 | 154 | 142 | 3/0 |
| 4/0 | 301 | 263 | 253 | 280 | 215 | 201 | 255 | 175 | 161 | 4/0 |
| 250 | 334 | 290 | 279 | 310 | 236 | 220 | 281 | 192 | 176 | 250 |
| 300 | 373 | 321 | 308 | 344 | 260 | 242 | 310 | 210 | 192 | 300 |
| 350 | 409 | 351 | 337 | 377 | 283 | 264 | 340 | 228 | 209 | 350 |
| 400 | 442 | 376 | 361 | 394 | 302 | 280 | 368 | 243 | 223 | 400 |
| 500 | 503 | 427 | 409 | 460 | 341 | 316 | 412 | 273 | 249 | 500 |
| 600 | 552 | 468 | 447 | 511 | 371 | 343 | 457 | 296 | 270 | 600 |
| 700 | 602 | 509 | 486 | 553 | 402 | 371 | 492 | 319 | 291 | 700 |
| 750 | 632 | 529 | 505 | 574 | 417 | 385 | 509 | 330 | 301 | 750 |
| 800 | 654 | 544 | 520 | 597 | 428 | 395 | 527 | 338 | 308 | 800 |
| 900 | 692 | 575 | 549 | 628 | 450 | 415 | 554 | 355 | 323 | 900 |
| 1000 | 730 | 605 | 576 | 659 | 472 | 435 | 581 | 372 | 338 | 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 | ||||||
Table B.310.8 Ampacities of Two or Three Insulated Conductors, Rated 0 Through 2000 Volts, Cabled Within an Overall (Two- or Three-Conductor) Covering, Directly Buried in Earth, Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure B.310.2, 100 Percent Load Factor, Thermal Resistance (Rho) of 90
| Size AWG or (kcmil) | 1 Cable (Fig. B.310.2, Detail 5) | 2 Cables (Fig. B.310.2, Detail 6) | 1 Cable (Fig. B.310.2, Detail 5) | 2 Cables (Fig. B.310.2, Detail 6) | Size AWG or (kcmil) | ||||
| 60°C (140°F) | 75°C (167°F) | 60°C (140°F) | 75°C (167°F) | 60°C (140°F) | 75°C (167°F) | 60°C (140°F) | 75°C (167°F) | ||
| Types | Types | ||||||||
| UF | RHW, THHW, THW, THWN, XHHW, USE | UF | RHW, THHW, THW, THWN, XHHW, USE | UF | RHW, THHW, THW, THWN, XHHW, USE | UF | RHW, THHW, THW, THWN, XHHW, USE | ||
| COPPER | ALUMINUM OR COPPER-CLAD ALUMINUM | ||||||||
| 8 | 64 | 75 | 60 | 70 | 51 | 59 | 47 | 55 | 8 |
| 6 | 85 | 100 | 81 | 95 | 68 | 75 | 60 | 70 | 6 |
| 4 | 107 | 125 | 100 | 117 | 83 | 97 | 78 | 91 | 4 |
| 2 | 137 | 161 | 128 | 150 | 107 | 126 | 110 | 117 | 2 |
| 1 | 155 | 182 | 145 | 170 | 121 | 142 | 113 | 132 | 1 |
| 1/0 | 177 | 208 | 165 | 193 | 138 | 162 | 129 | 151 | 1/0 |
| 2/0 | 201 | 236 | 188 | 220 | 157 | 184 | 146 | 171 | 2/0 |
| 3/0 | 229 | 269 | 213 | 250 | 179 | 210 | 166 | 195 | 3/0 |
| 4/0 | 259 | 304 | 241 | 282 | 203 | 238 | 188 | 220 | 4/0 |
| 250 | – | 333 | – | 308 | – | 261 | – | 241 | 250 |
| 350 | – | 401 | – | 370 | – | 315 | – | 290 | 350 |
| 500 | – | 481 | – | 442 | – | 381 | – | 350 | 500 |
| 750 | – | 585 | – | 535 | – | 473 | – | 433 | 750 |
| 1000 | – | 657 | – | 600 | – | 545 | – | 497 | 1000 |
| Ambient Temp. (°C) | Correction Factors | Ambient Temp. (°F) | |||||||
| 6-10 | 1.12 | 1.09 | 1.12 | 1.09 | 1.12 | 1.09 | 1.12 | 1.09 | 43-50 |
| 11-15 | 1.06 | 1.04 | 1.06 | 1.04 | 1.06 | 1.04 | 1.06 | 1.04 | 52-59 |
| 16-20 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 61-68 |
| 21-25 | 0.94 | 0.95 | 0.94 | 0.95 | 0.94 | 0.95 | 0.94 | 0.95 | 70-77 |
| 26-30 | 0.87 | 0.90 | 0.87 | 0.90 | 0.87 | 0.90 | 0.87 | 0.90 | 79-86 |