Determine Wire Size
Determine wire size using table 310.16 NEC2008 on page 70-148. Whether you are doing home electrical repair or on a electrical design job, simply calculate amperage (current) flow through the circuit and then apply the table.
Table 310.16
Allowable ampacities of Insulated Conductors rated 0 through 2000 Volts, 60°C through 90°C (140°F through 194°F), Not more than three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30°C(86°F)
| SIZE AWG OR KCMIL | COPPER | COPPER | COPPER | ALUMINUM | ALUMINUM | ALUMINUM | SIZE AWG OR KCMIL |
| _ | TYPE TW,UF | TYPES RHW ,THHW,THW, THWN,XHHW USE,ZW | RHW-2,THHN THHW,THW-2 (90°C) | TYPES TW,UF (60°C) | TYPES RHW THHW,THW THWN,XHHW USE | TYPES TBS,SA SIS,THHW SIZE AWG OR KCMIL | |
| 18 16 14 12 10 8 | _ _ 20 25 30 40 | _ _ 20 25 35 50 | 14 18 25 30 40 55 | _ _ _ 20 25 30 | _ _ _ 20 30 40 | _ _ _ 25 35 45 | _ _ _ 12 10 8 |
| 6 4 3 2 1 | 55 70 85 95 110 | 65 85 100 115 130 | 75 95 110 130 150 | 40 55 65 75 85 | 50 65 75 90 100 | 60 75 85 100 115 | 6 4 3 2 1 |
| 1/0 2/0 3/0 4/0 | 125 145 165 195 | 150 175 200 230 | 170 195 225 260 | 100 115 130 150 | 120 135 155 180 | 135 150 175 205 | 1/0 2/0 3/0 4/0 |
| 250 300 350 400 500 | 215 240 260 280 320 | 255 285 310 335 380 | 290 320 350 380 430 | 170 190 210 225 260 | 205 230 250 270 310 | 230 225 280 305 350 | 250 300 350 400 500 |
| 600 700 750 800 900 | 335 385 400 410 435 | 420 460 475 490 520 | 475 520 535 555 585 | 285 310 320 330 335 | 340 375 385 395 425 | 385 420 435 450 480 | 600 700 750 800 900 |
| 1000 1250 1500 1750 2000 | 435 495 520 545 560 | 545 590 625 650 665 | 615 665 705 735 750 | 375 405 435 455 470 | 445 485 520 545 560 | 500 545 585 615 630 | 1000 1250 1500 1750 2000 |
Apply table 310.16
Assume the current calculated result is 14A, cable type is copper THHN, insulated conductors rated at 90° C, Ignored some other factors,based on the table, wire size is 18 AWG. For practical safety application, recommended power wire size should be bigger than 12 AWG.
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Reference
National Electrical Code 2008
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