Sixty-eight rectangular sizes of C110 (ETP) copper bar, 1/16 through 3/4 inch thick. Area and weight are per foot of bar; DC resistance is at 20 °C; the skin-effect ratio is AC resistance divided by DC resistance at the bar temperature that goes with each rise (70, 90 and 105 °C). The ampacity columns are the 60 Hz ratings under the conditions stated above the tools.[1]
| Thick (in) | Wide (in) | Area (in²) | Weight (lb/ft) | DC R at 20 °C (µΩ/ft) | Skin ratio, 70 °C | Amps, 30 °C rise | Skin ratio, 90 °C | Amps, 50 °C rise | Skin ratio, 105 °C | Amps, 65 °C rise |
|---|---|---|---|---|---|---|---|---|---|---|
| 1/16 | 1/2 | 0.0312 | 0.121 | 264 | 1.00 | 103 | 1.00 | 136 | 1.00 | 157 |
| 1/16 | 3/4 | 0.0469 | 0.181 | 175 | 1.00 | 145 | 1.00 | 193 | 1.00 | 225 |
| 1/16 | 1 | 0.0625 | 0.241 | 132 | 1.00 | 187 | 1.00 | 250 | 1.00 | 285 |
| 1/16 | 1 1/2 | 0.0938 | 0.362 | 87.7 | 1.00 | 270 | 1.00 | 355 | 1.00 | 410 |
| 1/16 | 2 | 0.125 | 0.483 | 65.8 | 1.01 | 345 | 1.01 | 460 | 1.01 | 530 |
| 1/8 | 1/2 | 0.0625 | 0.241 | 132 | 1.00 | 153 | 1.00 | 205 | 1.00 | 235 |
| 1/8 | 3/4 | 0.0938 | 0.362 | 87.7 | 1.00 | 215 | 1.00 | 285 | 1.00 | 325 |
| 1/8 | 1 | 0.125 | 0.483 | 65.8 | 1.01 | 270 | 1.01 | 360 | 1.01 | 415 |
| 1/8 | 1 1/2 | 0.188 | 0.726 | 43.8 | 1.01 | 385 | 1.01 | 510 | 1.01 | 590 |
| 1/8 | 2 | 0.25 | 0.966 | 32.9 | 1.02 | 495 | 1.02 | 660 | 1.02 | 760 |
| 1/8 | 2 1/2 | 0.312 | 1.21 | 26.4 | 1.02 | 600 | 1.02 | 800 | 1.02 | 920 |
| 1/8 | 3 | 0.375 | 1.45 | 21.9 | 1.03 | 710 | 1.03 | 940 | 1.03 | 1,100 |
| 1/8 | 3 1/2 | 0.438 | 1.69 | 18.8 | 1.04 | 810 | 1.03 | 1,100 | 1.03 | 1,250 |
| 1/8 | 4 | 0.5 | 1.93 | 16.5 | 1.04 | 910 | 1.04 | 1,200 | 1.04 | 1,400 |
| 3/16 | 1/2 | 0.0938 | 0.362 | 87.7 | 1.00 | 195 | 1.00 | 260 | 1.00 | 300 |
| 3/16 | 3/4 | 0.141 | 0.545 | 58.4 | 1.01 | 270 | 1.01 | 360 | 1.01 | 415 |
| 3/16 | 1 | 0.188 | 0.726 | 43.8 | 1.01 | 340 | 1.01 | 455 | 1.01 | 520 |
| 3/16 | 1 1/2 | 0.281 | 1.09 | 29.3 | 1.02 | 480 | 1.02 | 630 | 1.02 | 730 |
| 3/16 | 2 | 0.375 | 1.45 | 21.9 | 1.03 | 610 | 1.03 | 810 | 1.03 | 940 |
| 3/16 | 2 1/2 | 0.469 | 1.81 | 17.5 | 1.04 | 740 | 1.04 | 980 | 1.03 | 1,150 |
| 3/16 | 3 | 0.562 | 2.17 | 14.6 | 1.05 | 870 | 1.05 | 1,150 | 1.04 | 1,350 |
| 3/16 | 3 1/2 | 0.656 | 2.53 | 12.5 | 1.07 | 990 | 1.06 | 1,300 | 1.06 | 1,500 |
| 3/16 | 4 | 0.75 | 2.9 | 11 | 1.09 | 1,100 | 1.08 | 1,450 | 1.07 | 1,700 |
| 1/4 | 1/2 | 0.125 | 0.483 | 65.8 | 1.01 | 240 | 1.01 | 315 | 1.01 | 360 |
| 1/4 | 3/4 | 0.188 | 0.726 | 43.8 | 1.01 | 320 | 1.01 | 425 | 1.01 | 490 |
| 1/4 | 1 | 0.25 | 0.966 | 32.9 | 1.02 | 400 | 1.02 | 530 | 1.02 | 620 |
| 1/4 | 1 1/2 | 0.375 | 1.45 | 21.9 | 1.03 | 560 | 1.03 | 740 | 1.03 | 860 |
| 1/4 | 2 | 0.5 | 1.93 | 16.5 | 1.04 | 710 | 1.04 | 940 | 1.04 | 1,100 |
| 1/4 | 2 1/2 | 0.625 | 2.41 | 13.2 | 1.06 | 850 | 1.06 | 1,150 | 1.06 | 1,300 |
| 1/4 | 3 | 0.75 | 2.9 | 11 | 1.08 | 990 | 1.08 | 1,300 | 1.07 | 1,550 |
| 1/4 | 3 1/2 | 0.875 | 3.38 | 9.4 | 1.10 | 1,150 | 1.09 | 1,500 | 1.09 | 1,750 |
| 1/4 | 4 | 1 | 3.86 | 8.23 | 1.12 | 1,250 | 1.11 | 1,700 | 1.10 | 1,950 |
| 1/4 | 5 | 1.25 | 4.83 | 6.58 | 1.16 | 1,500 | 1.15 | 2,000 | 1.14 | 2,350 |
| 1/4 | 6 | 1.5 | 5.8 | 5.49 | 1.18 | 1,750 | 1.17 | 2,350 | 1.17 | 2,700 |
| 1/4 | 8 | 2 | 7.73 | 4.11 | 1.23 | 2,250 | 1.22 | 3,000 | 1.21 | 3,450 |
| 1/4 | 10 | 2.5 | 9.66 | 3.29 | 1.27 | 2,700 | 1.26 | 3,600 | 1.25 | 4,200 |
| 1/4 | 12 | 3 | 11.6 | 2.74 | 1.31 | 3,150 | 1.30 | 4,200 | 1.28 | 4,900 |
| 3/8 | 3/4 | 0.281 | 1.09 | 29.3 | 1.02 | 415 | 1.02 | 550 | 1.02 | 630 |
| 3/8 | 1 | 0.375 | 1.45 | 21.9 | 1.03 | 510 | 1.03 | 680 | 1.03 | 790 |
| 3/8 | 1 1/2 | 0.562 | 2.17 | 14.6 | 1.05 | 710 | 1.04 | 940 | 1.04 | 1,100 |
| 3/8 | 2 | 0.75 | 2.9 | 11 | 1.08 | 880 | 1.08 | 1,150 | 1.07 | 1,350 |
| 3/8 | 2 1/2 | 0.938 | 3.62 | 8.77 | 1.12 | 1,050 | 1.10 | 1,400 | 1.09 | 1,600 |
| 3/8 | 3 | 1.12 | 4.35 | 7.35 | 1.15 | 1,200 | 1.14 | 1,600 | 1.13 | 1,850 |
| 3/8 | 3 1/2 | 1.31 | 5.06 | 6.28 | 1.18 | 1,350 | 1.16 | 1,800 | 1.15 | 2,100 |
| 3/8 | 4 | 1.5 | 5.8 | 5.49 | 1.20 | 1,500 | 1.19 | 2,000 | 1.18 | 2,350 |
| 3/8 | 5 | 1.88 | 7.26 | 4.38 | 1.24 | 1,800 | 1.23 | 2,400 | 1.22 | 2,800 |
| 3/8 | 6 | 2.25 | 8.69 | 3.66 | 1.27 | 2,100 | 1.26 | 2,800 | 1.24 | 3,250 |
| 3/8 | 8 | 3 | 11.6 | 2.74 | 1.33 | 2,650 | 1.31 | 3,550 | 1.30 | 4,100 |
| 3/8 | 10 | 3.75 | 14.5 | 2.19 | 1.38 | 3,200 | 1.36 | 4,300 | 1.35 | 4,900 |
| 3/8 | 12 | 4.5 | 17.4 | 1.83 | 1.42 | 3,700 | 1.40 | 5,000 | 1.38 | 5,800 |
| 1/2 | 1 | 0.5 | 1.93 | 16.5 | 1.04 | 620 | 1.04 | 820 | 1.04 | 940 |
| 1/2 | 1 1/2 | 0.75 | 2.9 | 11 | 1.08 | 830 | 1.08 | 1,100 | 1.07 | 1,250 |
| 1/2 | 2 | 1 | 3.86 | 8.23 | 1.12 | 1,000 | 1.11 | 1,350 | 1.10 | 1,550 |
| 1/2 | 2 1/2 | 1.25 | 4.83 | 6.58 | 1.16 | 1,200 | 1.15 | 1,600 | 1.14 | 1,850 |
| 1/2 | 3 | 1.5 | 5.8 | 5.49 | 1.20 | 1,400 | 1.19 | 1,850 | 1.18 | 2,150 |
| 1/2 | 3 1/2 | 1.75 | 6.76 | 4.7 | 1.24 | 1,550 | 1.22 | 2,100 | 1.21 | 2,400 |
| 1/2 | 4 | 2 | 7.73 | 4.11 | 1.26 | 1,700 | 1.25 | 2,300 | 1.24 | 2,650 |
| 1/2 | 5 | 2.5 | 9.66 | 3.29 | 1.32 | 2,050 | 1.30 | 2,750 | 1.29 | 3,150 |
| 1/2 | 6 | 3 | 11.6 | 2.74 | 1.36 | 2,400 | 1.34 | 3,150 | 1.33 | 3,650 |
| 1/2 | 8 | 4 | 15.5 | 2.06 | 1.42 | 3,000 | 1.40 | 4,000 | 1.39 | 4,600 |
| 1/2 | 10 | 5 | 19.3 | 1.65 | 1.47 | 3,600 | 1.45 | 4,800 | 1.44 | 5,500 |
| 1/2 | 12 | 6 | 23.2 | 1.37 | 1.52 | 4,200 | 1.51 | 5,600 | 1.50 | 6,400 |
| 3/4 | 4 | 3 | 11.6 | 2.74 | 1.42 | 2,050 | 1.40 | 2,750 | 1.38 | 3,150 |
| 3/4 | 5 | 3.75 | 14.5 | 2.19 | 1.48 | 2,400 | 1.46 | 3,250 | 1.44 | 3,750 |
| 3/4 | 6 | 4.5 | 17.4 | 1.83 | 1.52 | 2,800 | 1.50 | 3,750 | 1.48 | 4,300 |
| 3/4 | 8 | 6 | 23.2 | 1.37 | 1.60 | 3,500 | 1.58 | 4,700 | 1.56 | 5,400 |
| 3/4 | 10 | 7.5 | 29 | 1.1 | 1.67 | 4,200 | 1.64 | 5,600 | 1.62 | 6,500 |
| 3/4 | 12 | 9 | 34.8 | 0.914 | 1.72 | 4,900 | 1.69 | 6,500 | 1.67 | 7,500 |
Width beats thickness. For the same weight of copper, a wider, thinner bar carries more current because it has more surface to shed heat from and less skin effect. A 1/4 × 4 bar and a 1/2 × 2 bar weigh the same 3.86 lb/ft; at a 30 °C rise the first carries 1,250 A and the second 1,000 A. Thick bars earn their place where stiffness, short-circuit forces or bolt-hole area demand them, not for current.
The rise is a rule, not a choice. The three columns are the same bar at three temperatures. Which one a design may use comes from its standard (ANSI C37.20, IEC 61439 and their relatives) and from the joints: the CDA handbook cites C37.20 as allowing 65 °C only with silver-plated or equivalent terminations, and 30 °C otherwise. Cable insulation on connected conductors, typically 70 or 90 °C rated, often becomes the real limit.[2]
Skin effect is why big bars disappoint. At 60 Hz the current crowds toward the surface, and the ratio column shows the penalty: near 1.00 for thin bars, 1.7 for 3/4 × 12. Above a few thousand amps, two or more bars in parallel with a gap between them beat one very large bar. Parallel-bar and enclosed-bar ratings are not in this table.
What the table does not cover. Bars lying flat, bars in enclosures, bundled bars, DC service, altitude, ambients other than 40 °C, aluminum bar and short-circuit withstand all need their own data; the CDA busbar handbook and the standard governing the equipment are the places to look. For the machining side of a busbar, the bolted joint rules, bend radii and plating decisions, see the busbar design guide; for blank weight in any size, the metal weight calculator.
Send the drawing with bar size, temper, hole pattern and plating. We machine C110 bar to print, in lengths to 50 inches in one setup, and respond within one business day.