The square mil area for a two inch wide by 1 4 inch thick copper busbar is square mils

1-2 SQUARE MIL The square mil is a unit of measurement used to determine the cross-sectional area of a square or rectangular conductor (views A and B of figure 1-1). A square mil is defined as the area of a square, the sides of which are each 1 mil. To obtain the cross-sectional area of a square conductor, multiply the dimension of any side of the square by itself. For example, assume that you have a square conductor with a side dimension of 3 mils. Multiply 3 mils by itself (3 mils 3 mils). This gives you a cross-sectional area of 9 square mils. Figure 1-1.—Cross-sectional areas of conductors. Q1. State the reason for the establishment of a "unit size" for conductors. Q2. Calculate the diameter in MILS of a conductor that has a diameter of 0.375 inch. Q3. Define a mil-foot. To determine the cross-sectional area of a rectangular conductor, multiply the length times the width of the end face of the conductor (side is expressed in mils). For example, assume that one side of the rectangular cross-sectional area is 6 mils and the other side is 3 mils. Multiply 6 mils 3 mils, which equals 18 square mils. Here is another example. Assume that a conductor is 3/8 inch thick and 4 inches wide. The 3/8 inch can be expressed in decimal form as 0.375 inch. Since 1 mil equals 0.001 inch, the thickness of the conductor will be 0.001 0.375, or 375 mils. Since the width is 4 inches and there are 1,000 mils per inch, the width will be 4 1,000, or 4,000 mils. To determine the cross-sectional area, multiply the length by the width; or 375 mils 4,000 mils. The area will be 1,500,000 square mils. Q4. Define a square mil as it relates to a square conductor. CIRCULAR MIL The circular mil is the standard unit of measurement of a round wire cross-sectional area (view C of figure 1-1). This unit of measurement is found in American and English wire tables. The diameter of a round conductor (wire) used to conduct electricity may be only a fraction of an inch. Therefore, it is convenient to express this diameter in mils to avoid using decimals. For example, the diameter of a wire is expressed as 25 mils instead of 0.025 inch. A circular mil is the area of a circle having a diameter of 1 mil, as shown in view B of figure 1-2. The area in circular mils of a round conductor is obtained by squaring the diameter, measured in mils. Thus, a wire having a diameter of 25 mils has an area of 252, or 625 circular mils. To determine the number of square mils in the same conductor, apply the conventional formula for determining the area of a circle (A = pr2). In this formula, A (area) is the unknown and is equal to the cross-sectional area in square mils, p is the constant 3.14, and r is the radius of the circle, or half the diameter (D). Through substitution, A = 3.14, and (12.5) 2; therefore, 3.14 156.25 = 490.625

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Table 1: Ampacities

Ampacities of Copper No. 110 Busbars - Ampacities in the table below are for bus bars having an emissivity of 0.4. This was observed on samples exposed for 60 days in an industrial environment, and it is probably identical to that of bus bars in service.

Dimensions, In.	Area	Weight Per Foot, Lb	DC Resistance at 20° C, Microhms Per Ft
Square In.	Circular Mils, Thousands
1/16 x 1/2 1/16 x 3/4 1/16 x 1 1/16 x 1 1/2 1/16 x 2	0.0312 0.0469 0.0625 0.0938 0.125	39.7 59.7 79.6 119 159	0.121 0.181 0.241 0.362 0.483	264.0 175.0 132.0 87.7 65.8
1/8 x 1/2 1/8 x 3/4 1/8 x 1 1/8 x 1 1/2 1/8 x 2 1/8 x 2 1/2 1/8 x 3 1/8 x 3 1/2 1/8 x 4	0.0625 0.0938 0.125 0.188 0.250 0.312 0.375 0.438 0.500	79.6 119 159 239 318 397 477 558 636	0.241 0.362 0.483 0.726 0.966 1.21 1.45 1.69 1.93	132.0 87.7 65.8 43.8 32.9 26.4 21.9 18.8 16.5
3/16 x 1/2 3/16 x 3/4 3/16 x 1 3/16 x 1 1/2 3/16 x 2 3/16 x 2 1/2 3/16 x 3 3/16 x 3 1/2 3/16 x 4	0.0938 0.141 0.188 0.281 0.375 0.469 0.562 0.656 0.750	119 179 239 358 477 597 715 835 955	0.362 0.545 0.726 1.09 1.45 1.81 2.17 2.53 2.90	87.7 58.4 43.8 29.3 21.9 17.5 14.6 12.5 11.0
1/4 x 1/2 1/4 x 3/4 1/4 x 1 1/4 x 1 1/2 1/4 x 2 1/4 x 2 1/2 1/4 x 3 1/4 x 3 1/2 1/4 x 4 1/4 x 5 1/4 x 6 1/4 x 8 1/4 x 10 1/4 x 12	0.125 0.188 0.250 0.375 0.500 0.625 0.750 0.875 1.00 1.25 1.50 2.00 2.50 3.00	159 239 318 477 637 796 955 1,110 1,270 1,590 1,910 2,550 3,180 3,820	0.483 0.726 0.966 1.45 1.93 2.41 2.90 3.38 3.86 4.83 5.80 7.73 9.66 11.6	65.8 43.8 32.9 21.9 16.5 13.2 11.0 9.40 8.23 6.58 5.49 4.11 3.29 2.74
3/8 x 3/4 3/8 x 1 3/8 x 1 1/2 3/8 x 2 3/8 x 2 1/2 3/8 x 3 3/8 x 3 1/2 3/8 x 4 3/8 x 5 3/8 x 6 3/8 x 8 3/8 x 10 3/8 x 12	0.281 0.375 0.562 0.750 0.938 1.12 1.31 1.50 1.88 2.25 3.00 3.75 4.50	358 477 715 955 1,190 1,430 1,670 1,910 2,390 2,860 3,820 4,770 5,730	1.09 1.45 2.17 2.90 3.62 4.35 5.06 5.80 7.26 8.69 11.6 14.5 17.4	29.3 21.9 14.6 11.0 8.77 7.35 6.28 5.49 4.38 3.66 2.74 2.19 1.83
1/2 x 1 1/2 x 1 1/2 1/2 x 2 1/2 x 2 1/2 1/2 x 3 1/2 x 3 1/2 1/2 x 4 1/2 x 5 1/2 x 6 1/2 x 8 1/2 x 10 1/2 x 12	0.500 0.750 1.00 1.25 1.50 1.75 2.00 2.50 3.00 4.00 5.00 6.00	637 955 1,270 1,590 1,910 2,230 2,550 3,180 3,820 5,090 6,360 7,640	1.93 2.90 3.86 4.83 5.80 6.76 7.73 9.66 11.6 15.5 19.3 23.2	16.5 11.0 8.23 6.58 5.49 4.70 4.11 3.29 2.74 2.06 1.65 1.37
3/4 x 4 3/4 x 5 3/4 x 6 3/4 x 8 3/4 x 10 3/4 x 12	3.00 3.75 4.50 6.00 7.50 9.00	3,820 4,770 5,730 7,640 9,550 11,500	11.6 14.5 17.4 23.2 29.0 34.8	2.74 2.19 1.83 1.37 1.10 0.914

Dimensions, In.	30 °C Rise	50 °C Rise	65 °C Rise
Skin Effect Ratio at 70° C	60-Hz Ampacity,* Amp	Skin Effect Ratio at 90° C	60-Hz Ampacity, *Amp	Skin Effect Ratio at 105° C	60-Hz Ampacity, *Amp
1/16 x 1/2 1/16 x 3/4 1/16 x 1 1/16 x 1 1/2 1/16 x 2	1.00 1.00 1.00 1.00 1.01	103 145 187 270 345	1.00 1.00 1.00 1.00 1.01	136 193 250 355 460	1.00 1.00 1.00 1.00 1.01	157 225 285 410 530
1/8 x 1/2 1/8 x 3/4 1/8 x 1 1/8 x 1 1/2 1/8 x 2 1/8 x 2 1/2 1/8 x 3 1/8 x 3 1/2 1/8 x 4	1.00 1.00 1.01 1.01 1.02 1.02 1.03 1.04 1.04	153 215 270 385 495 600 710 810 910	1.00 1.00 1.01 1.01 1.02 1.02 1.03 1.03 1.04	205 285 360 510 660 800 940 1,100 1,200	1.00 1.00 1.01 1.01 1.02 1.02 1.03 1.03 1.04	235 325 415 590 760 920 1,100 1,250 1,400
3/16 x 1/2 3/16 x 3/4 3/16 x 1 3/16 x 1 1/2 3/16 x 2 3/16 x 2 1/2 3/16 x 3 3/16 x 3 1/2 3/16 x 4	1.00 1.01 1.01 1.02 1.03 1.04 1.05 1.07 1.09	195 270 340 480 610 740 870 990 1,100	1.00 1.01 1.01 1.02 1.03 1.04 1.05 1.06 1.08	260 360 455 630 810 980 1,150 1,300 1,450	1.00 1.01 1.01 1.02 1.03 1.03 1.04 1.06 1.07	300 415 520 730 940 1,150 1,350 1,500 1,700
1/4 x 1/2 1/4 x 3/4 1/4 x 1 1/4 x 1 1/2 1/4 x 2 1/4 x 2 1/2 1/4 x 3 1/4 x 3 1/2 1/4 x 4 1/4 x 5 1/4 x 6 1/4 x 8 1/4 x 10 1/4 x 12	1.01 1.01 1.02 1.03 1.04 1.06 1.08 1.10 1.12 1.16 1.18 1.23 1.27 1.31	240 320 400 560 710 850 990 1,150 1,250 1,500 1,750 2,250 2,700 3,150	1.01 1.01 1.02 1.03 1.04 1.06 1.08 1.09 1.11 1.15 1.17 1.22 1.26 1.30	315 425 530 740 940 1,150 1,300 1,500 1,700 2,000 2,350 3,000 3,600 4,200	1.01 1.01 1.02 1.03 1.04 1.06 1.07 1.09 1.10 1.14 1.17 1.21 1.25 1.28	360 490 620 860 1,100 1,300 1,550 1,750 1,950 2,350 2,700 3,450 4,200 4,900
3/8 x 3/4 3/8 x 1 3/8 x 1 1/2 3/8 x 2 3/8 x 2 1/2 3/8 x 3 3/8 x 3 1/2 3/8 x 4 3/8 x 5 3/8 x 6 3/8 x 8 3/8 x 10 3/8 x 12	1.02 1.03 1.05 1.08 1.12 1.15 1.18 1.20 1.24 1.27 1.33 1.38 1.42	415 510 710 880 1,050 1,200 1,350 1,500 1,800 2,100 2,650 3,200 3,700	1.02 1.03 1.04 1.08 1.10 1.14 1.16 1.19 1.23 1.26 1.31 1.36 1.40	550 680 940 1,150 1,400 1,600 1,800 2,000 2,400 2,800 3,550 4,300 5,000	1.02 1.03 1.04 1.07 1.09 1.13 1.15 1.18 1.22 1.24 1.30 1.35 1.38	630 790 1,100 1,350 1,600 1,850 2,100 2,350 2,800 3,250 4,100 4,900 5,800
1/2 x 1 1/2 x 1 1/2 1/2 x 2 1/2 x 2 1/2 1/2 x 3 1/2 x 3 1/2 1/2 x 4 1/2 x 5 1/2 x 6 1/2 x 8 1/2 x 10 1/2 x 12	1.04 1.08 1.12 1.16 1.20 1.24 1.26 1.32 1.36 1.42 1.47 1.52	620 830 1,000 1,200 1,400 1,550 1,700 2,050 2,400 3,000 3,600 4,200	1.04 1.08 1.11 1.15 1.19 1.22 1.25 1.30 1.34 1.40 1.45 1.51	820 1,100 1,350 1,600 1,850 2,100 2,300 2,750 3,150 4,000 4,800 5,600	1.04 1.07 1.10 1.14 1.18 1.21 1.24 1.29 1.33 1.39 1.44 1.50	940 1,250 1,550 1,850 2,150 2,400 2,650 3,150 3,650 4,600 5,500 6,400
3/4 x 4 3/4 x 5 3/4 x 6 3/4 x 8 3/4 x 10 3/4 x 12	1.42 1.48 1.52 1.60 1.67 1.72	2,050 2,400 2,800 3,500 4,200 4,900	1.40 1.46 1.50 1.58 1.64 1.69	2,750 3,250 3,750 4,700 5,600 6,500	1.38 1.44 1.48 1.56 1.62 1.67	3,150 3,750 4,300 5,400 6,500 7,500
* Applicable to typical in-service conditions (indoors, 40°C ambient temperature), horizontal run on edge, and free from external magnetic influences.