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Basis for selecting harness type

Author:SHUNGAL Click: Time:2021-10-13 15:59:34

Conductor type is also called conductor type. The first step of conductor selection is to determine the category of conductor. This paper mainly introduces the category of vehicle conductor and the basis of conductor type selection.

1 Classification of conductors

1) Classification by standard

According to different standards, low-voltage automobile wires are mainly divided into four series: national standard line, Japanese standard line, German standard line and American standard line.

The selection of wire type focuses on the environment and function of the harness. There are many subcategories for wires under each standard series, such as:

National standards: QVR, qvr-105, QFR, QVVR, etc;

German standard: flry-a, flry-b, flr4y, flr13y, etc;

Daily standard: AV, AVS, AVSS, Cavs, AVX, AEX, etc;

American Standard: GXL, twp, TXL, GPT, HDT, STS, etc.

The Japanese standard conductor is characterized by thin skin insulation and good flexibility; The national standard conductor is characterized by thick insulating skin, relatively soft and good ductility; The insulation skin of German standard conductor is thinner and flexible; American standard wire insulation skin is generally thermoplastic or thermosetting elastomer, as well as processed by irradiation process. The appropriate type of conductor can be selected according to the needs of users and different working environments. In the automotive industry, German markings are used most at present, and Japanese markings are mainly used by Japanese cars.

Reference standards for different series of wires (the online beam engineer's official account is returned to the "conductor standard"):

1) National standard cable reference standards: GB / T 8139, JB / T 8139, QC / T 730, QC / T 1037

2) Japanese standard cable reference standards: Jaso d608, Jaso D609, Jaso D611, JIS c3406

3) German standard cable reference standards: ISO 6722, din72550, DIN72551, din76772, VW 60306, LV 112 - 3

4) American standard cable reference standards: SAE j1128, SAE j1678, US car-21.

2) Classification by use

In terms of application, the wires on the automobile harness can be roughly divided into ordinary wires, twisted pair wires and shielded wires.

Ordinary conductors are the most widely used and will not be repeated.

Twisted pair is formed by winding two ordinary thin wires with insulating layer around each other in a certain proportion:

The principle of twisted pair is: if the interference generated by the external electromagnetic signal on the two conductors is equal in size and opposite in phase, the interference signals will cancel each other. Twisted pair is the simplest way to eliminate interference. Twisted pair can be used when some requirements are not very strict.

Aluminum foil is mainly used to shield the high-frequency electromagnetic wave, prevent the high-frequency electromagnetic wave from contacting with the network cable conductor, resulting in induced current and increasing crosstalk. The braided net is generally made of tinned round copper wire. It is mainly to prevent low-frequency electromagnetic wave interference. Its working principle is the same as that of aluminum foil.

Working principle of shielding wire: take the aluminum foil shielding wire as an example. When the high-frequency electromagnetic wave contacts the aluminum foil, according to Faraday's electromagnetic induction law, the electromagnetic wave will adhere to the aluminum foil surface and generate induced current. At this time, a conductor is needed to guide the induced current to the earth to avoid the interference of the induced current to the transmission signal. (therefore, it is generally required that one end of the shielding layer is grounded and the other end is suspended.)

The black wire in the aluminum foil shield wire is the grounding wire, and the braided mesh in the braided mesh shield wire is the grounding wire. Now, the aluminum foil shield wire is generally used, because its harness processing process is relatively simple.

Shielding is the most effective measure to avoid electromagnetic interference, because external interference electromagnetic waves will not pass through metal materials in the process of propagation, but will be forced to change direction and travel along the metal. Therefore, if the metal material is wrapped outside the equipment or conductor to be shielded for shielding and connected with the earth through the grounding wire, the interference electromagnetic wave will flow to the earth through the grounding wire, and the signal in the shielded conductor can be transmitted normally.

2. Properties of wires

The wires commonly used in automobile harness usually use multi strand stranded copper wires, and the insulating skin mostly uses PVC insulating materials, which should have the characteristics of temperature resistance, oil resistance, wear resistance, waterproof, anti-corrosion, oxidation resistance, flame retardant and so on.

1) Heat resistance

Wires with different temperature resistance grades shall be selected according to the working ambient temperature of harness wires. The wire type shall be selected for the harness design, with emphasis on the environment and function of the harness.

Wires in passenger compartment can be 90 ℃ temperature resistant; Wires with temperature resistance grade of 180 ℃ can be selected for engine compartment harness; The conductor crossing the above two areas shall select the conductor with temperature resistance grade meeting the temperature requirements of the two areas at the same time. The temperature resistance requirements of the area can be obtained through the temperature field, and then the selected conductor type shall be determined from the temperature resistance grade of each conductor.

2) Wear resistance

The conductor itself should be able to prevent insulator damage and leakage caused by wear and tear at the wiring part.

During the design, the conductor shall try to avoid contact with parts prone to vibration, so as to prevent abrasion and fracture of the harness. If unavoidable, wrapping tape or additional bellows can be used.

3) Flame retardancy

Flame retardancy refers to the regulation that the combustion time (speed) and range of parts are controlled within a certain range after ignition.

4) Bending property

Specify the repeated bending of parts requiring bending in the design. The bending degree, allowable bending times and ambient temperature of parts shall be set according to the service conditions. For example, the rubber sleeve for door shall reach 180 ° / 100000 times / - 30 ~ 80 ℃.

3 Determination of conductor type

The selection of conductor type should be based on platform. The following are some industry general principles for wire type selection:

As the current carrying capacity of the conductor will decrease with the increase of ambient temperature, the conductor with corresponding temperature resistance grade shall be selected according to the working environment of the harness.

The ambient temperature around the engine is high, and there are many corrosive gases and liquids. Therefore, high temperature, oil, vibration and friction resistant wires must be used;

The wire on the automatic transmission must be resistant to high temperature and hydraulic oil, and its temperature stability is good;

The conductor on the luggage compartment cover shall maintain its elasticity at low temperature, so the cold elastic conductor shall be selected to ensure its normal operation;

Shielded wires shall be used for weak signal sensors, such as knock sensor, crankshaft position sensor, ABS wheel speed sensor, etc;

High bending resistance of door wires frequently opened / closed;

The wires across the vehicle body shall have good flexural performance, etc.

Basis for selecting harness type
Conductor type is also called conductor type. The first step of conductor selection is to determine the category of conductor. This paper mainly introduces the category of vehicle conductor and the ba
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