What Is a Wire Harness?
A wire harness is a general term for a group of parts that are responsible for the connection between devices and that are bundled together with electric wires, terminals, and connectors attached to both ends of the wires to transmit various electric signals emitted from the devices.
Because multiple electric wires are necessary for the number of signals to be transmitted, and because the thickness and flexibility of the wires vary depending on the intended use and the size of the current flowing through them, they can be compared to “blood vessels” in human terms in terms of their function.
The most typical use of wire harnesses is in automobile wiring harnesses. Wiring harnesses are used around the engine, where the lead-acid batteries and other components that supply electricity to the car are mainly located, as well as around the driver’s seat, rear tail lights, and other areas of the car.
Recently, with the widespread use of hybrid and electric vehicles, there is a growing demand for products that are lighter and can withstand higher voltages, and the development of products with particularly high voltage resistance is underway.
Uses of Wire Harnesses
Wire harnesses are used to connect devices and equipment to transmit electrical signals from one to the other. Wire harnesses are also used in many other fields besides automobiles. Examples of applications are as follows:
1. Automobiles
The most typical use of wire harnesses is in automobiles. They are concentrated around the engine, which is the main power source. Starting from the engine periphery, they are connected to all parts of the automobile, including the air conditioner control panel located inside the automobile, and the brakes and rear tail lights located outside the automobile.
For ease of assembly and maintenance, the wiring harnesses are not connected by a single long wire but are divided into sections, such as “front, middle, and rear,” and are installed in the car. The connections between the divided wire harnesses are generally made via connectors.
In addition to engine applications, harnesses for sliding doors also exist. Sliding door applications are designed for smaller sizes and mobility.
2. Medical Equipment
Harnesses are also used inside medical equipment such as MRIs and CTs. Compared to automotive applications, where the wire harness itself has to pass through the limited space inside the vehicle while considering vibration and water damage, the shape of the wire harness itself is simple.
Instead, the reliability of information between connected devices is required, so the required performance in terms of noise reduction and electrical resistance tends to be high.
3. Production Facilities
Wire harnesses are also used in equipment used to produce electrical appliances and other products. Production lines in factories are long and are expected to be used for a long period, and in some cases, production lines are relocated, so long wire harnesses are often used.
In addition, wire harnesses are often trampled by both workers and heavy machinery in factories, and are often contaminated with oil and dirt, so high durability of wire harnesses tends to be required.
Types of Wire Harnesses
There are different types of wire harnesses, ranging from low-voltage wire harnesses for general applications to high-voltage wire harnesses for high voltage applications.
1. Low-voltage wire Harnesses
Low-voltage wire harnesses are used to supply power from the 12V lead-acid batteries used in conventional gasoline-powered vehicles to various components.
2. High-Voltage Wire Harness
High-voltage wire harnesses are wire harnesses for use in electric and hybrid vehicles, which have been in increasing demand in recent years.
Motors are used to drive electric and hybrid vehicles, which require high power output to drive the motors. In addition, the control unique to electric and hybrid vehicles, such as using the motor as a generator during deceleration to charge the battery with regenerative energy to extend the cruising distance, requires higher heat resistance performance to withstand more complex system control.
Therefore, conventional wire harnesses cannot withstand high voltages and large currents, and high-voltage wire harnesses have been developed.
3. Aluminum Wire Harnesses
Aluminum wire harnesses are wire harnesses in which the conductor of the wires has been changed from conventional copper to aluminum.
Although it is expected to be 30~40% lighter than conventional copper, it has lower electrical conductivity and lower melting point than copper and thus has issues with heat resistance and the processability of crimp terminals attached to the terminals.
As the number of wire harnesses increases with the improvement of automobile safety and comfort, and with the shift to automated driving, there is concern that the weight of the car body will increase, and the demand for lightweight aluminum wire harnesses is increasing.
Principles of Wire Harnesses
Wire harnesses consist mainly of corrugated tubes, clips, connectors, terminals, wires, and tapes.
1. Corrugated Tubing
A corrugated tube is a bellows-shaped tube used as a protective material for wire harnesses. Since it is mainly used to protect electric wires, heat resistance, and shape restoration properties are required.
There are two types, one with slits and the other without slits, for ease of processing during installation, so it is necessary to select one according to the need. Polypropylene resin is often used as a material.
2. Clips
Clips are used to secure wires when crawling wire harnesses. Various types exist according to the size and shape of the harness.
3. Connectors
Connectors are used to connect electrical wiring. Generally, male and female connectors come as a set. By crimping dedicated terminals onto stripped wires and inserting them into connectors, connections can be made easily without soldering or twisting wires together.
4. Terminal
Terminals are attached to the ends of wires. Like connectors, terminals also come in male and female sets and are used to connect wires by touching the terminals when connecting to a connector.
Generally, wires and terminals are joined by crimping.
5. Electric Wire
Wires are used to supply electric power and transmit electrical signals to connected devices. Copper is mainly used for wires because of its good balance of price and conductivity, but the number of wires used in wire harnesses is expected to increase in the future as systems become more complex. As a result, there is a growing demand for lighter weight wires themselves, and the development of aluminum wires is underway.
6. Tape
Tape is used to restrain electric wires and protect insulated parts. Since wire harnesses require insulation and flame retardance, vinyl tape made of vinyl chloride is mainly used.
Other Information on Wire Harnesses
1. About Wire Harnesses Factories
The manufacturing of wire harnesses involves many processes that are carried out by hand, so full automation of production is less advanced than in other manufacturing industries. For this reason, production is often carried out in countries with low labor costs, and the ratio of female employees, who are suited to light work, tends to be high.
2. The Future of Wire Harnesses
The future of wire harnesses is expected to shift from conventional wire harnesses to high-voltage wire harnesses for electric vehicles and lightweight aluminum wire harnesses.