Keywords: electrical wiring; good wiring; aircraft assembly 1.2 Wire gauge number of the wire Concerned about surprises Tag: Aircraft skin System wiring Demodulation circuit Assembly process Cabling system Previous: Hard turning technology and key technologies Next: Mechanical properties of aluminum alloy cables
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introduction
Since the aircraft began to electrify, the aircraft wiring has undertaken more and more tasks, not only the traditional transmission and distribution functions, but also the transmission of information such as flight control, engine, landing gear, avionics and other important systems. Features.
Definition of electromagnetic compatibility (EMC): In the same electromagnetic environment, the system can not affect the normal operation due to the interference of other systems, and does not affect the interference of other systems.
Therefore, the wiring system must have the ability to resist external electromagnetic interference, and at the same time be able to prevent the internal transmission signal from radiating energy to the outside.
1. Identification of wire harnesses and wires
Wires are the most basic components of electrical circuits. It can be said that where there are electrical circuits, there are wires.
1.1 Definitions and differences between wires, cables and wire bundles
Wire: A single solid or twisted conductor wrapped under the same layer of insulating material is called a wire.
Cable: A wire whose structure conforms to any of the following definitions may be referred to as a cable.
(1) Multi-conductor conductors consisting of two or more independent insulated conductors wrapped under the same jacket;
(2) twisted conductors of two or more independent insulated conductors twisted together;
(3) A shielded conductor consisting of one or more independent insulated conductors wrapped in a metal braided shield;
(4) A radio frequency conductor consisting of a single insulated center conductor and a metal braided outer conductor.
Wire bundle: A combination of wires and/or cables that are bundled and secured together, that is, a wire bundle.
As can be seen from the above definition, there is sometimes no strict distinction between wires and cables.
The wire gauge number of the wire is a number that characterizes the cross-sectional area of ​​the conductor of the wire. Usually expressed in terms of the American Wire Gauge (AWG). The larger the wire gauge number, the smaller the cross-sectional area of ​​the conductor. The smaller the wire gauge number, the larger the cross-sectional area of ​​the conductor.
1.3 The color of the wire
The color of the wire is generally used only in the identification of two or more twisted wires. Its purpose is to facilitate the worker to identify the wire to be found from a plurality of twisted wires. The color code of the wire is mostly represented by the first letter of the color, such as "B" (Blue) for blue, "G" (Green) for green, "K" (Black) for black, and "O" for Orange, "R, W, Y" represent red, white and yellow, respectively.
1.4 Wire harness number
Each Wire Bundle number consists of the English letter W plus a set of four digits derived from the harness drawing number. Therefore, the first part of the wire number is "WXXXX". Among them, the four digit "XXXX" is "0000" and "8999". “9001†to “9999†are reserved for the customer to name the new wire harness number.
1.5 wire serial number
The serial number of a wire indicates the serial number of a wire in a bundle of wires. Generally, a single wire is different from a double or multiple stranded wires, and the first digit of the serial number is different. The first digit of the serial number of a single conductor is "0", the first digit of the serial number of the twisted conductor is "2", and so on. The first digits of the twisted pair and the twisted pair are respectively "3" and "4".
The serial number of the wire is determined by the number of wire harness wires to be four or three digits. The wire serial number is specified differently for different aircraft.
1.6 wire number
In general, the Boeing aircraft's wire number includes the wire harness number, wire serial number, wire gauge number, and color code (if applicable), as shown in Figure 1 below. On Boeing airplanes, the wire number is either printed directly on each. On the wire, either use the identification label to stick it in place. The wire number on the wire corresponds to the wire number marked on the circuit diagram, which is convenient for maintenance personnel to identify. 
2. Classification of wires
The classification of wires is based on the classification and combination of the interference characteristics of each wire. Considering the high density of wire mounting on modern aircraft, the type of wire should be minimized under conditions that effectively control interference coupling.
Conductors can be divided into six categories according to their structure, performance and use: Class I (primary power line), class II (secondary power line), class III (control line), class IV (low level sensitive line), class V (Isolation line) and VI (system wiring).
2.1 Class I - primary power cord
This type of line is the wiring between the power supply and the electrical load, including:
a, transmission of 115/200V400Hz single-phase or three-phase AC wiring between the power supply and the electrical load;
b. Route 36V AC or 28V DC to the electrical load.
For example, general examples of electrical loads are: AC motors, heaters, general lighting systems, relays, and other solenoid operated devices.
Some electronic equipment, if equipped with a power transformer and isolated from the power line, should also be part of the electrical equipment. All excitation circuits of the self-aligning machine belong to Class I.
2.2 Class II————Secondary power cord
This type of line is the wiring between the electronic load and the instrument load and power supply, including:
a, the transmission of 36V AC and 28V DC wiring to the electronic and instrument load;
b. Transmission of secondary DC voltage within 5KV.
For example: electronic and instrumentation loads include solid-state circuit radios, in-machine talkers, autopilots, computer warnings, anti-skid systems, automatic spoilers, and more. Except for the excitation circuit and the signal "three-phase" circuit of the self-aligning machine, all the wirings including the 28V DC line filter belong to the class 2 wiring.
2.3 Class III—control line
This type of line refers to a wire that is connected to a device or component that is working for a short period of time. It produces undesired transient disturbances while it is working, and is not affected by transient disturbances. For example, wires to relay coils and solenoids belong to this type of line.
When this type of line is not used (not used on civil aircraft), it can be reclassified as Class I and Class II.
2.4 Class IV————Low-sensitive line
This type of line refers to the sensitive circuit composed of wires and cables used by sensitive equipment. The circuits include:
a, analog signal circuit, audio and video circuits, sensitivity control, volume control circuit, etc.;
b, all signal circuits and bridge circuits of the self-aligning machine;
c, low level digital input circuit;
d, low level demodulation circuit.
2.5 V class - isolation line
This type of line refers to the antenna coaxial cable and the flight function cable, which is used to transmit functional signals between the device and the antenna or as a cable to connect the special electrical functions necessary for flight.
For example: all transmission lines, waveguides and coaxial cables connected to radio and radar equipment, electric igniters, fire alarms, fuel oil, hydraulic oxygen systems, etc., main power output feeders should be wired according to Category 5.
Circuits belonging to Category 5 except coaxial cables are considered to be very sensitive to external electrical environments and should be isolated.
This type of cable cannot be combined with other types or even similar cables. This combination of antennas can only be combined if the shielding is sufficient to provide compatibility. Each cable of the combination must be isolated.
The cables of the receiver (or transmitter) can be combined, the coaxial cables of the transceivers cannot be combined, and the dual-purpose cables for receiving and transmitting cannot be combined.
2.6 VI———System wiring
This class was developed for the installation of dense wiring areas to facilitate the installation of individual systems.
This type of wire harness is composed of Class II and Class IV wires. Class I and Class V lines cannot appear in the VI class harness. A system's VI-type harness cannot be combined with another system's VI-type harness. The wiring of the Category VI line can only be determined on the aircraft if approved by the engineering review department. These cables and their locations are clearly identified on the engineering drawings.
The main power control and regulation wires shall be routed in accordance with Class VI.
3. Wire routing method
a, bundles of wires carrying approximately the same level of interference and similar types of interference;
b, the wire bundle with large interference and the wire harness with small interference should be isolated from each other;
c, using space separation to isolate one type of wire from another type of wire;
d. When different types of wires or cables have to be laid together (for example, when passing through the same hole in the frame), the wires and cables should be separated as far as possible on each side of the frame hole;
e, all wires and cables should be dispersed as far as possible, and pay attention to the cable's orientation and laying, so as to minimize the interference coupling control. Such as: the aircraft metal structure and equipment installed in the machine can be used to provide shielding;
f, in the main power circuit of the aircraft, if there is a backup cable, the backup cable should be laid as far as possible, if possible on each side of the fuselage;
g, all power cord (I, II) cables and any cables greater than 5 amps, as close as possible to the metal skin;
h. The power line, sensitive line and isolation line should not be close to the electromagnetic interference emission line. All, sensitive lines, isolation lines and antenna feeder lines should be away from the opening of the aircraft skin or non-metallic structure parts;
i. When the sensitive line and the isolation line have to be laid close to the power line, lay the cable at a right angle as much as possible. Different types of cables enter the device from different directions as much as possible;
j, different types of wires should not be used on the same electrical connector. In particular, the isolation cable and the sensitive cable should not use the same electrical connector as the power cable or the interference cable;
k, multiple power lines should be used to supply power from the main power supply to the components in a device to reduce the interaction between components;
l, to suppress the DC-150KHz radiation or induced magnetic field, the twisted wire should be used, the twist rate should be no less than 23 revolutions per meter (only valid when twisted with the positive and return lines);
m, wherever the return current is required, a double-core twisted wire or coaxial wire should be used;
n, when twisted wire is used, the twisted wire should be kept to the terminal. Such as until electrical connectors, corners, wiring boards, junction boxes;
o, if the power line is only allowed to use single-core wire wiring, then the phase line or the positive line is laid as close as possible to the neutral line or DC return line;
p, wire wiring, in order to prevent damage into two or more components of the open line, you need to use the subscript letters to give a reasonable mark, and meet the requirements of the navigation mark "aircraft circuit function code and wire color";
q, in addition to all the wires and cables installed in the machine, in addition to the GJB1014 (General Requirements for Aircraft Cabling), the wire harness should also have an electromagnetic compatibility category.
Within 1 cm behind the identification of the cable harness, the category of electromagnetic compatibility is marked with the number θ. Expressed as "E" for electromagnetic compatibility; Roman numeral I-VI is indicated as a category. 
This article mainly introduces the definition of aircraft wires and their identification, classification and routing guidelines. The wiring method is an important factor affecting the electromagnetic compatibility of aircraft systems. The entire aircraft from the nose to the tail, from the left wing to the right wing, from the vertical tail to the landing gear, no one has no electrical lines.
In the process of aircraft assembly, good wiring is effective to ensure the smoothness of the aircraft electrical circuit. Specifically, there are two main functions: first, to ensure the integrity of the various control systems of the aircraft, that is, to ensure the signal transmission of the aircraft control system; second, to ensure the power supply of all the power systems of the aircraft. , that is, to ensure the power distribution of the power system.
In general, good wiring is a very important part of the aircraft assembly process, which effectively guarantees the integrity, safety and reliability of the aircraft system. At present, our national aircraft is still in the development stage. The performance indicators of the wiring method in the assembly process of the aircraft have yet to be continuously improved and improved one by one in the future.
references:
[1] Liu Mingguang. Aircraft Electric. Guangzhou: Sun Yat-sen University Press, 2008.3
[2] Shao Zikai, Dai Cizhuang. HB 6524-1991. Classification and wiring requirements for electromagnetic compatibility of aircraft wires and cables. Department of Aeronautics and Astronautics.1991.8(end) 
