Step 5-To find the total harness capacity, multiply the total number of size 22 wires by the derated capacity (25 × 7.2 = 180.0 amps) and add to that the number of size 20 wires multiplied by the derated capacity (10 × 9.6 = 96.8 amps) and multiply the sum by the 20 percent harness capacity factor. Derate the size 20 harness rating by multiplying 11.2 amps by 0.86 to get 9.6 amps. Derate the size 22 harness rating by multiplying 8.4 amps by 0.86 to get 7.2 amps. Note that the wire must be derated by a factor of 0.86 (found on the vertical axis). Look for 35,000 feet (on the horizontal axis) since that is the altitude at which the aircraft is operating. Step 4-Refer to the altitude derating curve of Figure 5.
#100 amp aluminum wire size free#
Derate the size 20 free air rating by multiplying 21.5 by 0.52 to get 11.2 amps in-harness rating. Step 3-Derate the size 22 free air rating by multiplying 16.2 by 0.52 to get 8.4 amps in harness rating. They should not be used in applications where they are subjected to excessive vibration, repeated bending, or frequent disconnection from screw termination. They should also have additional support at terminations, such as connector grommets, strain relief clamps, shrinkable sleeving, or telescoping bushings. As a general practice, wires smaller than size #20 should be provided with additional clamps and be grouped with at least three other wires. Consideration should be given to the use of high-strength alloy conductors in small-gauge wires to increase mechanical strength. Wires containing less than 19 strands must not be used. If it is desirable to use wire sizes smaller than #20, particular attention should be given to the mechanical strength and installation handling of these wires (e.g., vibration, flexing, and termination). The maximum allowable operating temperature of insulated conductors varies with the type of conductor insulation being used. Allowance must be made for the influence of external heating on the allowable conductor current, and each case has its own specific limitations. When electrical conductors are installed in locations where the ambient temperature is relatively high, the heat generated by external sources constitutes an appreciable part of the total conductor heating.
Thus, to protect the insulation from too much heat, the current through the conductor must be maintained below a certain value. If the conductor is insulated, the heat generated in the conductor is not so readily removed as it would be if the conductor were not insulated.
The temperature of the wire rises until the heat radiated, or otherwise dissipated, is equal to the heat generated by the passage of current through the line.
If the source maintains a constant voltage at the input to the lines, any variation in the load on the line causes a variation in line current and a consequent variation in the IR drop in the line.However, large conductors are more expensive, heavier, and need more substantial support. The use of large conductors reduces the resistance and therefore the I2 R loss. Allowable power loss (I2 R loss) in the line represents electrical energy converted into heat.Wires must have sufficient mechanical strength to allow for service conditions.Several factors must be considered in selecting the size of wire for transmitting and distributing electric power.
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