Electrical Power Systems Technology

Electrical Power Distribution Systems 235

way. They will be located in a foundry area where temperatures reach

50°C. The ampacity for No. 10 RHW copper wire is 30 A (from Table 8-5).

The correction factor for an RHW-insulated conductor at 50°C ambient tem-

perature is 0.75 (Table 8-6). Therefore,

30 amperes × 0.75 = 22.5 amperes

Table 8-4. Allowable Ampacities of Single Conductance in Free Air

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Copper Aluminum

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With RH, With RH,

With R, T, RHW With R, T, RHW, TH

TW TH, THW TW THW

Wire Size Insulation Insulation Insulation Insulation

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AWG 14 20 20

12 25 25 20 20

10 40 40 30 30

8 55 65 45 55

6 80 95 60 75

4 105 125 80 100

3 120 145 95 115

2 140 170 110 135

1 165 195 130 155

0 195 230 150 180

00 225 265 175 210

000 260 310 200 240

0000 300 360 230 280

MCM 250 340 405 265 315

300 375 445 290 350

350 420 505 330 395

400 455 545 355 425

500 515 620 405 485

600 575 690 455 545

700 630 755 500 595

750 655 785 515 620

800 680 815 535 645

900 730 870 580 700

1000 780 935 625 750

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USE OF INSULATION IN POWER DISTRIBUTION SYSTEMS

Synthetic insulation for wire and cable is classified into two broad cat-

egories—thermosetting and thermoplastic. The mixtures of materials within

each of these categories are so varied as to make the available number of