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FLAT BUS
Flat bus conductors. because of their shape , can be confined to a minimum of space and can be easily joined to one another without cumbersome connector fittings. The bars can be readily bent to take corners and formed to make right angle bends for connections such as taps and and angle couplings. The large surface areas provide a means for dissipating generated heat where high currents are employed.
Because of skin-effect and proximity-effect flat bus conductors have a limited capacity when conducting alternating current. However, the capacity may be improved to some degree by planned location of the buses to minimize these losses. For direct current transmission in flat bar busses, in as much as the I2R loss is the only important factor, flat bus conductors provided with ample carrying cross section and ventilation can have considerably high current capacities.
Owing to the shape of the flat bus its high bending strength is only attained in the plane parallel to its major surface, while the bending strength in the plane at right angles to this surface is very low. This low strength necessitates the busses being supported at close intervals to eliminate bending and distortion.
Copper Bus
Size of Straps |
Number and Capacity of Straps in Amps. |
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| Thick. | Width | 1 | 2 | 3 | 4 |
| 1/8" 1/8" 1/8" 1/8" 1/4" 1/4" 1/4" |
3/4" 1" 2" 3" 2" 3" 4" |
200 250 500 750 700 1000 1350 |
350 450 900 1300 1200 1650 2250 |
1850* 2500* | 2250* |
Notes:
1. Capacities are at 60 cycles.
2. Courtesy Anaconda Wire Cable Co.
3.Current carrying capacity of copper strap connections for 30° C. rise. Bar faces
vertical, spacing between bars equal to bar thickness.
* For direct current, use 1,000 amperes per sq. in.
Aluminum Bus
Bars arranged with faces vertical. Capacities are at 60 cycles for A.C. |
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| Size Inches | Number and total capacity of Bar in Amps. |
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1 |
2 |
3 |
4 |
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| A.C. | D.C. | A.C. | D.C. | A.C. | D.C. | A.C. | D.C. | |
| 3 X 1/4 4 X 1/4 5 X 1/4 6 X 1/4 8 X 1/4 3 X 3/8 4 X 3/8 5 X 3/8 6 X 3/8 8 X 3/8 |
760 1000 1230 1450 1700 910 1190 1430 1650 2000 |
780 1040 1290 1530 1830 945 1260 1550 1800 2220 | 1400 1650 2000 2300 2750 1600 2080 2400 2700 3100 |
1500 1770 2200 2600 3300 1900 2400 2850 3300 4050 |
1750 2100 2500 2800 3400 2200 2600 2900 3300 4000 |
1900 2360 2950 3400 4400 2550 3100 3700 4450 5700 |
2050 2500 3000 3350 4100 2500 2900 3350 3750 4600 |
2300 3000 3750 4350 5700 3050 3800 4600 5400 7100 |
Notes:
- Ratings are for 30° C hot-spot rise over 40° C ambient temperature in still but unconfined air.
- For 35° C hot-spot rise increase rating 10 per cent. For multiple-bar arrangement 35° C hot-spot rise approximately equals 30° C rise.
- For multiple-bar arrangements, the space between bars is equal to the bar thickness.
- Ratings must be reduced for phase spacing less than 18 inches.
- Courtesy of the Aluminum Company of America