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Low-voltage cables play a vital role in the operation of automotive circuits. As an indispensable part of the circuit, they can not only transmit signals and energy but also ensure the safety and stability of the circuit.

Selecting suitable wire materials and structures helps the normal operation of the automotive electrical system and meets the driving requirements. With the development of modern automotive technology, low-voltage cables will move towards a more advanced and intelligent direction.

I. Overview and Characteristics of Low-Voltage Cable

Overview

Automotive low-voltage cables include low voltage and high voltage and are the main body of onboard circuits. They connect different electronic components of automobiles to achieve power transmission, which is of great significance for the safe operation of automobiles. The materials of low-voltage cables include copper-clad steel wires, copper-clad aluminum wires, etc., which are composite wires with a copper layer coating steel wires or aluminum wires. Advanced coating welding technology is adopted, and low-voltage high-frequency signals travel along the copper layer surface. Increasing the thickness of the copper layer can improve signal transmission efficiency.

Characteristics

High strength: It combines the conductivity of pure copper and the high-strength characteristics of metals such as steel and aluminum. The superposition of these beneficial effects not only improves conductivity, thermal conductivity but also enhances corrosion resistance and oxidation resistance.
Strong heat resistance: Since the temperature in the engine compartment is very high, low-voltage cables need to have certain heat resistance to operate at high temperatures. Moreover, the harnesses in the engine compartment may come into contact with oil, so they also need certain oil resistance.
Good insulation: Low-voltage harnesses also have certain insulation properties to prevent current leakage and short circuits. Adequate insulation can also isolate other electronic components, playing a shielding and protective role.
Low cost: The cost of copper is very high, and using copper-clad steel wires or copper-clad aluminum wires can appropriately reduce the amount of copper used, thus reducing the cost of wires.

II. Selection of Low-Voltage Harness Wires in Automobiles

Selection based on the usage environment: When selecting the types of low-voltage cable, the environment where the harness is located should be considered to ensure the safety and stability of the automobile. For example, the heat resistance of harnesses arranged in different positions in the car varies; the harnesses arranged at the bottom of the car need to consider the vibration frequency during driving, as well as the mud, sand, and debris brought by the wheels at the bottom, and wires with good wear resistance and corrosion resistance should be used. For harnesses arranged in areas with high humidity, the influence of corrosive liquid infiltration needs to be considered, and materials with good insulation properties should be selected. When selecting wires for the door and window areas, whether they have bending resistance needs to be considered.
Selection based on color: The selection of low-voltage cable colors should follow the requirements of QCT414 - 2016 "Color Specification and Model Preparation Method for Automotive Wires (Cables)". As shown in Figure 1, a single color is usually preferred, followed by two colors. For the grounding wires in automobiles, black wires are generally selected; for sensor negative wires, signal negative wires, etc., brown wires or wires with brown as the main color are used. For main power supply wires, such as the positive wire of the battery and the starter power supply harness, red is usually selected. Other power supply wires generally use yellow, red, and other colors. And the wires in the same connector should be of different colors.
Selection of wire diameter: Based on the rated current of automotive electrical equipment, combined with wire parameters and temperature conditions, and at the same time, the rated current-carrying capacity of the wire also needs to be within a certain range to select an appropriate wire diameter. Meanwhile, the smoking time of the wire must be consistent with the melting time of the fuse, and the minimum smoking current must reach more than 130% of the fuse capacity. If the selected fuse capacity is 5.00 A, it may melt, and the minimum smoking current is 5 × 135% = 6.75 A. From the smoking time, if a wire with a diameter of 0.50 mm² is selected, the smoking start time exceeds 1,000 s. From the current-carrying time of the fuse, the overload 135% fuse can carry current for about 550 - 1,000 s, and the fuse can protect the circuit. If the minimum smoking current does not reach 125% of the fuse capacity, a wire specification with a diameter > 0.50 mm² should be selected.
Selection based on application range: The nominal cross-sectional areas of low-voltage cable include 0.50 mm², 0.75 mm², 1.00 mm², 1.50 mm², 2.00 mm², 2.50 mm², and 4.00 mm², etc. Wires with different cross-sectional areas have different load current values, and corresponding wires should be selected according to actual needs. For instrument lights, indicator lights, and door lights in automobiles, wires with a specification of 0.50 mm² should be selected; for front and rear lights, brake lights, and license plate lights, a specification of 0.75 mm² is required; for turn signals and fog lights, a specification of 1.00 mm² is suitable; for headlights and horns, a specification of 1.50 mm² should be selected; for generator hubs, grounding wires, and other main power supply wires, a specification of 2.50 - 4.00 mm² should be selected. For wires that carry large currents (such as the grounding wire of the battery and the positive wire of the power source), their wire diameters are very large, generally exceeding 12.00 mm², so these wires do not need to be incorporated into the main harness.
Selection based on temperature: The selection of low-voltage cable should be based on the operating temperature of the automobile, and wires with various temperature resistance grades should be used. As shown in Figure 2, wires with a temperature resistance grade of 90 °C are generally selected for the passenger compartment of the automobile; wires with a temperature resistance grade of 180 °C are selected for the engine compartment because the temperature in the engine compartment is very high during operation. In addition, for the wires that cross between the passenger compartment and the engine compartment, the temperature resistance grade needs to meet the requirements of both areas. Generally, a temperature field is used to obtain the temperature resistance requirements of this area, and then the wire type to be selected is determined from the temperature resistance grades of different wires.

III. Application Range of Low-Voltage Cable in Automobiles

Application in ignition and power supply systems: In the ignition system of automobiles, low-voltage cables need to be connected to ignition coils, ignition switches, and spark plugs. Their function is to transmit power to the spark plugs and ignite the fuel mixture by sparking. In this case, the low-voltage cable in the ignition system must have certain insulation properties when selected and applied to avoid electric shock. At the same time, they also need to have good conductivity to ensure the energy and stability of ignition. In addition, low-voltage harnesses also have certain applications in the power supply system. For example, in the vehicle power supply system, low-voltage cables are responsible for transmitting current to the vehicle's power system to support vehicle operation. (The application of low-voltage cable in this module requires certain safety and durability to cope with high current and long-term operation)
Application in sensor and control systems: The intelligent driving of automobiles depends on the operation of sensors and control systems. Low-voltage cables are connected to speed sensors, temperature sensors, pressure sensors, and other sensors to transmit the signals generated by the sensors to the control unit. This requires low-voltage cable to have sufficient anti-interference performance and good signal transmission efficiency. In the automotive safety system, low-voltage cables connect the engine control unit, braking system, and parking assist system. Ensure that various signals are transmitted to different control units and actuators, so low-voltage cables need to ensure the accuracy of signal transmission and achieve high-speed transmission.
Application in lighting systems: The lighting system of automobiles is generally powered by low voltage, and automotive lamps are loads that are sensitive to voltage. Therefore, the voltage drop of the wires needs to be verified. If the voltage drop exceeds a reasonable range, the cross-sectional area of the wire should be increased to make the operating voltage of the load meet the requirements. Taking the lamps of a certain automobile as an example, the normal operating voltage of the lamp load is between 25 - 28 Therefore, a low-voltage cable with an appropriate wire diameter should be selected, neither too large nor too small. Generally, a wire with a diameter of 0.50 mm² is more suitable. If the wire diameter is too small, it will affect the brightness of the bulb, and if it is too large, it will burn out the bulb. Therefore, when selecting low-voltage cable for lamps, the wire diameter should be comprehensively considered according to the circuit and operating voltage.
Application in the engine compartment and trunk: In the engine compartment of automobiles, the application of low-voltage harnesses includes engine parts, ignition devices, etc., which require heat resistance, oil resistance, and flame retardancy. Copper-clad steel wires can be used. Because of the proximity to the engine, low-voltage harnesses also require certain anti-interference and anti-vibration properties. In the luggage compartment, it is necessary to select harnesses suitable for the rear part of the vehicle and the doors to ensure flexibility and anti-electromagnetic interference performance. Copper-clad aluminum wires are more suitable. For positions such as the instrument panel, operation panel, and under the carpet in the cockpit, low-voltage cable should also be used and ensure certain wear resistance and heat resistance.
Application in grounding wires: Grounding wires play a very important role in the entire automotive circuit system. They need to guide the current to the negative pole of the battery to ensure the stable operation of the circuit system. Using copper-clad aluminum, a new type of wire material, in grounding wires not only has good conductivity but also can reduce the use of copper materials and costs.

IV. Development Trends of Automotive Low-Voltage Cable

Meeting higher usage requirements: With the continuous development of automotive technology and the popularization of electrified and hybrid vehicles, low-voltage cable also needs to be further optimized and improved. New-era automobiles need to install more advanced electrical systems to meet higher signal and power transmission requirements. Future low-voltage cables must also support higher current loads and supply power to more electrical equipment to make vehicle operations safer, more stable, and more reliable. Copper-clad aluminum is a composite material composed of copper and aluminum, with a layer of copper covering the aluminum surface. This wire material not only has the lightweight characteristics of aluminum but also has good conductivity. However, since grounding wires need to withstand the high temperature of automobiles and the corrosion of external substances, anti-corrosion work must also be done, and interference and friction at assembly parts must be reduced, because this will lead to insulation damage. To avoid damage to the external part of the grounding wire due to friction and prevent it from contacting vibrating parts, thus protecting the grounding wire. If optimization design cannot be carried out, operations such as tape wrapping and adding bellows should be adopted.
Developing towards semiconductors: Nowadays, semiconductor technology has made great progress, and future automotive low-voltage cables will also integrate this technology. Wires integrating semiconductor elements and chips can achieve more diversified functions, such as data transmission, signal processing, and automatic diagnosis. It can not only improve the intelligence of the entire system but also save space.
Developing towards lightweight: As the automotive industry pays more and more attention to fuel efficiency and environmental protection, automotive low-voltage cable will also continue to develop towards lightweight. By using lighter materials and optimizing the structural design, the weight of wires can be reduced, reducing fuel consumption and pollution emissions. For example, replacing traditional copper wires with copper-clad steel and copper-clad aluminum can make the vehicle electrical system more lightweight and efficient.
Developing towards intelligence: Shortly, with the continuous development of autonomous driving and Internet technology, low-voltage cables will also introduce high-speed transmission technology and sensor integration technology to achieve comprehensive and efficient electrical connections. Make automotive intelligent devices more advanced and achieve high-speed transmission of signals, including connections of radars, large-size display screens, antennas, etc., making vehicles develop towards intelligence and networking.

V. Conclusion

In conclusion, by comprehensively considering and selecting suitable low-voltage cable materials and structures and applying them reasonably, the stable operation of the automotive system and the safety of vehicle occupants can be ensured.

At the same time, with the continuous development of this technology, low-voltage cables will also move towards a more advanced, lightweight, and intelligent direction and create more benefits.