3, are installed in a common raceway or cable, the derating

factors shown above shall apply to the number of power and lighting (Articles 210, 215, 220, and 230) conductors only. Exception No. 2: For conductors installed in cable trays, the provisions of Section 318-11 shall apply. Exception No. 3: Derating factors shall not apply to conductors in nipples having a length not exceeding 24 inches (610 mm). Exception No. 4: Derating factors shall not apply to underground conductors entering or leaving an outdoor trench if those conductors have physical protection in the form of rigid metal conduit, intermediate metal conduit, or rigid nonmetallic conduit having a length not exceeding 10 feet (3.05 m) above grade and the number of conductors does not exceed four. Exception No. 5: For other loading conditions, adjustment factors and ampacities shall be permitted to be calculated under Section 310-15(b). (FPN): See Appendix B, Table B-310-11 for adjustment factors for more than three current-carrying conductors in a raceway or cable with load diversity. (b) More than One Conduit, Tube, or Raceway. Spacing between conduits, tubing, or raceways shall be maintained. 9. Overcurrent Protection. Where the standard ratings and settings of overcurrent devices do not correspond with the ratings and settings allowed for conductors, the next higher standard rating and setting shall be permitted. Exception: As limited in Section 240-3. 70-180 NATIONAL ELECTRICAL CODE 10. Neutral Conductor. (a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit need not be counted when applying the provisions of Note 8. (b) In a 3-wire circuit consisting of 2-phase wires and the neutral of a 4-wire, 3-phase wye-connected system, a common conductor carries approximately the same current as the other conductors and shall be counted when applying the provisions of Note 8. (c) On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads such as electric-discharge lighting, electronic computer/data processing, or similar equipment, there are harmonic currents present in the neutral conductor, and the neutral shall be considered to be a current-carrying conductor. 11. Grounding or Bonding Conductor. A grounding or bonding conductor shall not be counted when applying the provisions of Note 8. Table 310-61. Conductor Application and Insulation Maximum Trade Type Operating Application Outer Name Letter Temperature Provision Insulation Covering Medium MV-75* 75° C Dry or wet Thermoplastic Jacket, voltage MV-85* 85° C locations or Sheath, solid MV-90* 90° C rated 2001 Thermosetting or Armor dielectric volts and higher *Insulation and outer coverings that meet the requirements as flame-retardant limitedsmoke and are so listed shall be permitted to be designated limited-smoke with the suffix LS after the Code type designation. Table 310-62. Thickness of Insulation for 601-2000-Volt Nonshielded Types RHH and RHW, in Mils Conductor Size AWG-kcmil A B 14-10 80 60 8 80 70 6-2 95 70 1-2/0 110 90 3/0-4/0 110 90 213-500 125 105 501-1000 140 120 Note: Column A insulations are limited to natural, SBR, and butyl rubbers. Note: Column B insulations are materials such as cross-linked polyethylene, ethylene propylene rubber, and composites thereof. Table 310-63. Thickness of Insulation and Jacket for Nonshielded Solid Dielectric Insulated Conductors Rated 2001 to 8000 Volts, in Mils 5001-8000 Volts 100 Percent Conductor-Size Insulation Level Wet or Dry AWG-kcmil 2001-5000 Volts Locations Multi- Dry Locations Single Conductor Wet or Dry Locations Single Conductor Conductor* Without Multi- Jacket With Jacket Single Conductor Conductor* Insulation Insulation Jacket Insulation Jacket Insulation Insulation Jacket Insulation 8 110 90 30 125 80 90 180 80 180 6 110 90 30 125 80 90 180 80 180 4-2 110 90 45 125 80 90 180 95 180 1-2/0 110 90 45 125 80 90 180 95 180 3/0-4/0 110 90 65 125 95 90 180 110 180 ARTICLE 310 - CONDUCTORS FOR GENERAL WIRING 213-500 120 90 65 140 110 90 210 110 210 501-750 130 90 65 155 125 90 235 125 235 751-1000 130 90 65 155 125 90 250 140 250 *Note: Under a common overall covering such as a jacket, sheath, or armor. 70-181 70-182 NATIONAL ELECTRICAL CODE Table 310-64. Thickness of Insulation for Shielded Solid Dielectric Insulated Conductors Rated 2001 to 35,000 Volts, in Mils Conductor 2001- Size 5000 25,001- 28,001- AWG-kcmil Volts 5001-8000 8001-15,000 15,001-25,000 28,000 35,000 100 133 100 133 100 133 100 100 Per- Per- Per- Per- Per- Per- Per- Percent cent cent cent cent cent cent cent insuinsu- insuinsu- insuinsu- insuinsu- lation lation lation lation lation lation lation lation level level level level level level level level 8 90 - - - - - - - - 6-4 90 115 140 - - - - - - 2 90 115 140 175 215 - - - - 1 90 115 140 175 215 260 345 280 - 1/0-1000 90 115 140 175 215 260 345 280 345 *Definitions: 100 Percent Insulation Level. Cables in this category shall be permitted to be applied where the system is provided with relay protection such that ground faults will be cleared as rapidly as possible but, in any case, within 1 minute. While these cables are applicable to the great majority of cable installations that are on grounded systems, they shall be permitted to be used also on other systems for which the application of cables is acceptable, provided the above clearing requirements are met in completely deenergizing the faulted section. 133 Percent Insulation Level. This insulation level corresponds to that formerly designated for ungrounded systems. Cables in this category shall be permitted to be applied in situations where the clearing time requirements of the 100 percent level category cannot be met, and yet there is adequate assurance that the faulted section will be deenergized in a time not exceeding 1 hour. Also, they shall be permitted to be used where additional insulation strength over the 100 percent level category is desirable. ARTICLE 310 - CONDUCTORS FOR GENERAL WIRING 70-183 Table 310-67. Ampacities of Insulated Single Copper Conductor Cables Triplexed in Air Based on Conductor Temperature of 90°C (194°F) and Ambient Air Temperature of 40°C (104°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 65 - 6 90 100 4 120 130 2 160 170 1 185 195 1/0 215 225 2/0 250 260 3/0 290 300 4/0 335 345 250 375 380 350 465 470 500 580 580 750 750 730 1000 880 850 Table 310-68. Ampacities of Insulated Single Aluminum Conductor Cables Triplexed in Air Based on Conductor Temperature of 90°C (194°F) and Ambient Air Temperature of 40°C (104°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 50 - 6 70 75 4 90 100 2 125 130 1 145 150 1/0 170 175 2/0 195 200 3/0 225 230 4/0 265 270 250 295 300 350 365 370 500 460 460 750 600 590 1000 715 700 70-184 NATIONAL ELECTRICAL CODE Table 310-69. Ampacities of Insulated Single Copper Conductor Isolated in Air Based on Conductor Temperature of 90°C (194°F) and Ambient Air Temperature of 40°C (104°F) Conductor Size 2001-5000 Volts 5001-15,000 Volts 15,001-35,000 Volts AWG-kcmil Ampacity Ampacity Ampacity 8 83 - - 6 110 110 - 4 145 150 - 2 190 195 I 1 225 225 225 1/0 260 260 260 2/0 300 300 300 3/0 345 345 345 4/0 400 400 395 250 445 445 440 350 550 550 545 500 695 685 680 750 900 885 870 1000 1075 1060 1040 1250 1230 1210 1185 1500 1365 1345 1315 1750 1495 1470 1430 2000 1605 1575 1535 Table 310-70. Ampacities of Insulated Single Aluminum Conductor Isolated in Air Based on Conductor Temperature of 90°C (194°F) and Ambient Air Temperature of 40°C (104°F) Conductor Size 2001-5000 Volts 5001-15,000 Volts 15,001-35,000 Volts AWG-kcmil Ampacity Ampacity Ampacity 8 64 - - 6 85 87 - 4 115 115 - 2 150 150 - 1 175 175 175 1/0 200 200 200 2/0 230 235 230 3/0 270 270 270 4/0 310 310 310 250 345 345 345 350 430 430 430 500 545 535 530 750 710 700 685 1000 855 840 825 1250 980 970 950 1500 1105 1085 1060 1750 1215 1195 1165 2000 1320 1295 1265 ARTICLE 310 - CONDUCTORS FOR GENERAL WIRING 70-185 Table 310-71. Ampacities of an Insulated Three-Conductor Copper Cable Isolated in Air Based on Conductor Temperature of 90°C (194°F) and Ambient Air Temperature of 40°C (104°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 59 - 6 79 93 4 105 120 2 140 165 1 160 185 1/0 185 215 2/0 215 245 3/0 250 285 4/0 285 325 250 320 360 350 395 435 500 485 535 750 615 670 1000 705 770 Table 310-72. Ampacities of an Insulated Three-Conductor Aluminum Cable Isolated in Air Based on Conductor Temperature of 90°C (194°F) and Ambient Air Temperature of 40°C (104°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 46 - 6 61 72 4 81 95 2 110 125 1 125 145 1/0 145 170 2/0 170 190 3/0 195 220 4/0 225 255 250 250 280 350 310 345 500 385 425 750 495 540 1000 585 635 70-186 NATIONAL ELECTRICAL CODE Table 310-73. Ampacities of an Insulated Triplexed or Three Single Conductor Copper Cables in Isolated Conduit in Air Based on Conductor Temperature of 90°C (194°F) and Ambient Air Temperature of 40°C (104°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 55 - 6 75 83 4 97 110 2 130 150 1 155 170 1/0 180 195 2/0 205 225 3/0 240 260 4/0 280 295 250 315 330 350 385 395 500 475 480 750 600 585 1000 690 675 Table 310-74. Ampacities of Insulated Triplexed or Three Single Conductor Aluminum Cables in Isolated Conduit in Air Based on Conductor Temperature of 90°C (194°F) and Ambient Air Temperature of 40°C (104°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 43 - 6 58 65 4 76 84 2 100 115 1 120 130 1/0 140 150 2/0 160 175 3/0 190 200 4/0 215 230 250 250 255 350 305 310 500 380 385 750 490 485 1000 580 565 ARTICLE 310 - CONDUCTORS FOR GENERAL WIRING 70-187 Table 310-75. Ampacities of an Insulated Three-Conductor Copper Cable in Isolated Conduit in Air Based on Conductor Temperature of 90°C (194°F) and Ambient Air Temperature of 40°C (104°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 52 - 6 69 83 4 91 105 2 125 145 1 140 165 1/0 165 195 2/0 190 220 3/0 220 250 4/0 255 290 250 280 315 350 350 385 500 425 470 750 525 570 1000 590 650 Table 310-76. Ampacities of an Insulated Three-Conductor Aluminum Cable in Isolated Conduit in Air Based on Conductor Temperature of 90°C (194°F) and Ambient Air Temperature of 40°C (104°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 41 - 6 53 64 4 71 84 2 96 115 1 110 130 1/0 130 150 2/0 150 170 3/0 170 195 4/0 200 225 250 220 250 350 275 305 500 340 380 750 430 470 1000 505 550 70-188 NATIONAL ELECTRICAL CODE Table 310-77. Ampacities of Three Single Insulated Copper Conductors in Underground Electrical Ducts (Three Conductors per Electrical Duct) Based on Ambient Earth Temperature of 20°C (68°F), Electrical Duct Arrangement per Figure 310-1, 100 percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperature 90°C (194°F) One Circuit (See Figure 310-1, Detail 1) Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 64 6 85 90 4 110 115 2 145 155 1 170 175 1/0 195 200 2/0 220 230 3/0 250 260 4/0 290 295 250 320 325 350 385 390 500 470 465 750 585 565 1000 670 640 Three Circuits (See Figure 310-1, Detail 2) Size 8 56 6 73 77 4 95 99 2 125 130 1 140 145 1/0 160 165 2/0 185 185 3/0 210 210 4/0 235 240 250 260 260 350 315 310 500 375 370 750 460 440 1000 525 495 Six Circuits (See Figure 310-1, Detail 3) Size 8 48 6 62 64 4 80 82 2 105 105 1 115 120 1/0 135 135 2/0 150 150 3/0 170 170 4/0 195 190 250 210 210 350 250 245 500 300 290 750 365 350 1000 410 390 ARTICLE 310 - CONDUCTORS FOR GENERAL WIRING 70-189 Table 310-78. Ampacities of Three Single Insulated Aluminum Conductors in Underground Electrical Ducts (Three Conductors per Electrical Duct) Based on Ambient Earth Temperature of 20°C (68°F), Electrical Duct Arrangement per Figure 310-1, 100 percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperature of 90°C (194°F) One Circuit (See Figure 310-1, Detail 1) Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 50 - 6 66 70 4 86 91 2 115 120 1 130 135 1/0 150 155 2/0 170 175 3/0 195 200 4/0 225 230 250 250 250 350 305 305 500 370 370 750 470 455 1000 545 525 Three Circuits (See Figure 310-1, Detail 2) Size 8 44 - 6 57 60 4 74 77 2 96 100 1 110 110 1/0 125 125 2/0 145 145 3/0 160 165 4/0 185 185 250 205 200 350 245 245 500 295 290 750 370 355 1000 425 405 Six Circuits (See Figure 310-1, Detail 3) Size 8 38 - 6 48 50 4 62 64 2 80 80 1 91 90 1/0 105 105 2/0 115 115 3/0 135 130 4/0 150 150 250 165 165 350 195 195 500 240 230 750 290 280 1000 335 320 70-190 NATIONAL ELECTRICAL CODE Table 310-79. Ampacities of Three Insulated Copper Conductors Cabled 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 310-1, 100 percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperature 90°C (194°F) One Circuit (See Figure 310-1, Detail 1) Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 59 - 6 78 88 4 100 115 2 135 150 1 155 170 1/0 175 195 2/0 200 220 3/0 230 250 4/0 265 285 250 290 310 350 355 375 500 430 450 750 530 545 1000 600 615 Three Circuits (See Figure 310-1, Detail 2) Size 8 53 - 6 69 75 4 89 97 2 115 125 1 135 140 1/0 150 160 2/0 170 185 3/0 195 205 4/0 225 230 250 245 255 350 295 305 500 355 360 750 430 430 1000 485 485 Six Circuits (See Figure 310-1, Detail 3) Size 8 46 - 6 60 63 4 77 81 2 98 105 1 110 115 1/0 125 130 2/0 145 150 3/0 165 170 4/0 185 190 250 200 205 350 240 245 500 290 290 750 350 340 1000 390 380 ARTICLE 310 - CONDUCTORS FOR GENERAL WIRING 70-191 Table 310-80. Ampacities of Three Insulated Aluminum Conductors Cabled 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 310-1, 100 percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperature 90°C (194°F) One Circuit (See Figure 310-1, Detail 1) Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity 8 46 - 6 61 69 4 80 89 2 105 115 1 120 135 1/0 140 150 2/0 160 170 3/0 180 195 4/0 205 220 250 230 245 350 280 295 500 340 355 750 425 440 1000 495 510 Three Circuits (See Figure 310-1, Detail 2) Size 8 41 6 54 59 4 70 75 2 90 100 1 105 110 1/0 120 125 2/0 135 140 3/0 155 160 4/0 175 180 250 190 200 350 230 240 500 280 285 750 345 350 1000 400 400 Six Circuits (See Figure 310-1, Detail 3) Size 8 36 - 6 46 49 4 60 63 2 77 80 1 87 90 1/0 99 105 2/0 110 115 3/0 130 130 4/0 145 150 250 160 160 350 190 190 500 230 230 750 280 275 1000 320 315 70-192 NATIONAL ELECTRICAL CODE Table 310-81. Ampacities of Single Insulated Copper Conductors Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure 310-1, 100 percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperature 90°C (194°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity One Circuit- 3 Conductors (See Figure 310-1, Detail 9) 8 110 6 140 130 4 180 170 2 230 210 1 260 240 1/0 295 275 2/0 335 310 3/0 385 355 4/0 435 405 250 470 440 350 570 535 500 690 650 750 845 805 1000 980 930 Two Circuits- 6 Conductors (See Figure 310-1, Detail 10) 8 100 I 6 130 120 4 165 160 2 215 195 1 240 225 1/0 275 255 2/0 310 290 3/0 355 330 4/0 400 375 250 435 410 350 520 495 500 630 600 750 775 740 1000 890 855 For SI units: one inch = 25.4 millimeters. ARTICLE 310 - CONDUCTORS FOR GENERAL WIRING 70-193 Table 310-82. Ampacities of Single Insulated Aluminum Conductors Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure 310-1, 100 percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperature 90°C (194°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity One Circuit- 3 Conductors (See Figure 310-1, Detail 9) 8 85 - 6 110 100 4 140 130 2 180 165 1 205 185 1/0 230 215 2/0 265 245 3/0 300 275 4/0 340 315 250 370 345 350 445 415 500 540 510 750 665 635 1000 780 740 Two Circuits— 6 Conductors (See Figure 310-1, Detail 10) 8 80 6 100 95 4 130 125 2 165 155 1 190 175 1/0 215 200 2/0 245 225 3/0 275 255 4/0 310 290 250 340 320 350 410 385 500 495 470 750 610 580 1000 710 680 For SI units: one inch = 25.4 millimeters. 70-194 NATIONAL ELECTRICAL CODE Table 310-83. Ampacities of Three Insulated Copper Conductors Cabled within an Overall Covering (Three-Conductor Cable), Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure 310-1, 100 percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperature 90°C (194°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity One Circuit (See Figure 310-1, Detail 5) 8 85 6 105 115 4 135 145 2 180 185 1 200 210 1/0 230 240 2/0 260 270 3/0 295 305 4/0 335 350 250 365 380 350 440 460 500 530 550 750 650 665 1000 730 750 Two Circuits (See Figure 310-1, Detail 10) 8 80 - 6 100 105 4 130 135 2 165 170 1 185 195 1/0 215 220 2/0 240 250 3/0 275 280 4/0 310 320 250 340 350 350 410 420 500 490 500 750 595 605 1000 665 675 For SI units: one inch = 25.4 millimeters. ARTICLE 310 - CONDUCTORS FOR GENERAL WIRING 70-195 Table 310-84. Ampacities of Three Insulated Aluminum Conductors Cabled within an Overall Covering (Three-Conductor Cable), Directly Buried in Earth Based on Ambient Earth Temperature of 20°C (68°F), Arrangement per Figure 310-1, 100 percent Load Factor, Thermal Resistance (RHO) of 90, Conductor Temperature 90°C (194°F) Conductor Size 2001-5000 Volts 5001-35,000 Volts AWG-kcmil Ampacity Ampacity One Circuit (See Figure 310-1, Detail 5) 8 65 - 6 80 90 4 105 115 2 140 145 1 155 165 1/0 180 185 2/0 205 210 3/0 230 240 4/0 260 270 250 285 300 350 345 360 500 420 435 750 520 540 1000 600 620 Two Circuits (See Figure 310-1, Detail 6) 8 60 - 6 75 80 4 100 105 2 130 135 1 145 150 1/0 165 170 2/0 190 195 3/0 215 220 4/0 245 250 250 265 275 350 320 330 500 385 395 750 480 485 1000 550 560 For SI units: one inch = 25.4 millimeters. 70-196 NATIONAL ELECTRICAL CODE Notes to Tables 310-69 through 310-84 (FPN): For ampacities calculated in accordance with the following Notes 1 and 2, reference IEEE/ICEA "Power Cable Ampacities," Vol. I and II (IPCEA Pub. No. P-46-426) and the "References" therein for availability of all factors and constants. 1. Ambients Not in Tables. Ampacities at ambient temperatures other than those shown in the tables shall be determined by means of the following formula: I₂ = I₁ TC - TA2 - DELTA TD TC - TA₁ - DELTA TC Where: I₁ = Ampacity from tables at ambient TA₁. I₂ = Ampacity at desired ambient TA2. TC = Conductor temperature in degrees C. TA₁ = Surrounding ambient from tables in degrees C. TA2 = Desired ambient in degrees C. DELTA TD = Dielectric loss temperature rise. 2. Grounded Shields. Ampacities shown in Tables 310-69, 310-70, 310- 81, and 310-82 are for cable with shields grounded at one point only. Where shields are grounded at more than one point, ampacities shall be adjusted to take into consideration the heating due to shield currents. 3. Electrical Duct Bank Configuration. Ampacities shown in Tables 310- 77, 310-78, 310-79, and 310-80 shall apply only where the cables are located in the outer electrical ducts of the electrical duct bank. Ampacities for cables located in the inner electrical ducts of the electrical duct bank shall be determined by special calculations. 4. Burial Depth of Underground Circuits. For applications where burial depths must be deeper than shown in the underground ampacity tables, the following ampacity derating factor shall be permitted to be used: 6 percent per increased foot of depth for all values of Rho. No rating change is required where the burial depth is decreased. 5. Thermal Resistivity. Thermal resistivity, as used in this Code, refers to the heat transfer capability through a substance by conduction. It is the reciprocal of thermal conductivity and is designated Rho and expressed in the units °C-cm/watt. 6. Electrical Ducts Utilized in Figure 310-1. Spacings between electrical ducts (raceways) as defined in Figure 310-1 shall be permitted to be less than specified in Figure 310-1, where ducts (raceways) enter equipment enclosures from underground, without reducing the ampacity of conductors contained within such ducts (raceways). ARTICLE 310 - CONDUCTORS FOR GENERAL WIRING 70-197 4 7.5" Detail 1 7.5" 7.5" V 7.5" 7.5",7.5" 11.5"x11.5" Electrical duct bank 7.5" One electrical duct D Detail 2 7.5 7.51 7.5 19"x19" Electrical duct bank Detail 3 Detail 4 Three electrical ducts 19"x27" 27"x27" Electrical duct bank Electrical duct bank Or Six electrical ducts Nine electrical ducts Or 0 , = 7.5' 7.5 7.5 .5 27"x11.5" Electrical duct bank Three electrical ducts 7.5 7.5 27"x19" Electrical duct bank Six electrical ducts 24" 24" Detail 5 Detail 6 Detail 7 Detail 8 Buried 3 Buried 3 Buried triplexed Buried triplexed cables conductor conductor cables (1 circuit) (2 circuits) cable cables 7.5" 7.5 7.5" 7.5 24" 7.5" 7.5" Detail 9 Detail 10 Buried single conductor Buried single conductor cables (1 circuit) cables (2 circuits) Notes for all details: Legend 1. Minimum burial depths to top electrical ducts or cables shall be in accordance with Section 710-4(b). Maximum depth to the top Backfill of electrical duct banks shall be 30 inches and maximum depth to (earth or concrete) the top of direct buried cables shall be 36 inches. Electrical duct 2. Burial depths shall be permitted to be increased in part(s) of the duct run to avoid underground obstructions without Cable or cables decreasing the rated ampacity of the conductors. The total length of parts of the duct run increased in depth to avoid obstructions must be less than 25 percent of the total run length, or else the ampacity reduction factor of Note 4 of Tables 310-69 through 310-84 shall be applied. 3. For SI units: one inch = 25.4 millimeters; one foot = 305 millimeters. Figure 310-1. Cable Installation Dimensions for Use with Tables 310-77 through 310-84. 70-198 NATIONAL ELECTRICAL CODE