HomeTips & GuidesTypes of wire insulation: When it comes to automotive wires and cables

Types of wire insulation: When it comes to automotive wires and cables

The wires and cables used in automobiles play a crucial role in the safety and functioning of the vehicle. The durability of these cables and wires largely depends on the insulation layer, as the layer protects the wire from various exposed elements. So, let’s further discuss their different types of wire insulation.

Table of Contents

What do you understand about wire insulation?

Insulation is a non-conductive material layer covering the conductor to protect it against environmental factors such as chemicals, heat, water, and mechanical stress. 

This same layer is called dielectric in the case of radio frequency or RF cables. Insulation also protects against leakage of electric current from the wire so that it does not come in contact with other nearby cables and wires. 

A cable’s life and effectiveness largely depend on the insulation quality.

Sparks explosion between wires

Sparks explosion between wires

The function of automotive wire insulation:

As discussed above, insulation protects the cable and the wire against many factors. In automobile applications, insulation mainly has two roles:

Protects cables against corrosion:

As you know, copper in automotive wires is a very active metal; it readily reacts with oxygen and moisture in the air. 

Thus, protecting individual strands of wire in a cable or wire bundle is very difficult as air and moisture penetrate even in the plastic insulators.

So, the best solution for their protection is to plate the wires before the stranding process

There is common silver plating on the wires, but the best is to do tin plating as it is a simple process and protects wires against chemicals.

In earlier times, when plastic did not exist, twisted wire strands had rubber coatings, followed by a cotton braid. 

A shellac compound coating finally covered it. However, this type of coating was brittle and attracted fungi.

Later, when plastic came, most wires had plastic coverings such as PVC or polyvinyl chloride plastic. However, plastic is porous and allows contaminant inflow and outflow, especially in non-plated copper wires.

Finally, the best solution was to construct a wire jacket made of Teflon. It stays soft and flexible in its entire operating range. 

However, pure Teflon is prone to abrasion damage. Thus, the industry experts came up with a solution. 

They covered Teflon with a layer of PVC jacket, but the cost increased. Another problem with Teflon is that it emits toxic fumes in fire events.

Protects against heat:

PVC insulation is one of the options for protecting cables and wires from heat. 

There are two types of PVC insulated write; one rated for 80 degrees Celsius and another for 105 degrees Celsius. 

Teflon, another insulating layering material, does not melt even at temperatures up to 400-500 degrees Fahrenheit.

Generally, the temperature outside the engine compartment is up to 180 degrees Fahrenheit only. 

However, the temperature inside the engine compartment can go as high as 300 degrees Fahrenheit.

 The wire insulation readily gets damaged at this temperature when chemicals like brake fluid, cleaning solvents or fuel are added.

Thus, the wires and cables in the engine compartment use Tefzel as its insulation. This substance is somewhat related to the Teflon only. 

Although it has little temperature resistance, it has high abrasion resistance properties.

Engine wiring harness

Engine wiring harness

Low-voltage automotive wires and their insulation:

Among many low-volt automotive wires, the common ones are the GPT and cross-link PE wires. The main difference between them is in their insulation layer properties.

GPT wire:

GPT refers to the thermoplastic layer around the General Purpose Wire, the general wiring for the vehicles’ standard electrical circuits. 

On a bare wire of copper, technicians extrude the PVC layer through a die after heating it.

 This layer can withstand temperatures of -45 to +85 degrees Celsius and work up to 60 volts.

GPT costs less than cross-link. You can find it both in the cabin and under-the-hood applications. 

However, GPT is not as good as cross-link when handling heat and liquid chemicals.

 Thus, you must avoid using it near the engine or in places exposed to chemical liquids.

To create a cross-link PE wire, technicians extrude the material via a tube, applying pressure and heat to get cross-linked. 

During the cross-linking process, the insulation molecules change to a different state.

Cross-link PE wire is best for a temperature range of -51 degrees Celsius- +125 degrees Celsius. 

Also, it can work up to a voltage of 60 volts. Further, the wire shows high resistance against grease, gasoline, oil, moisture, and most acids.

It is safe to use cross-link wire for fuse blocks in engines and systems where the wire may get exposed to open elements and air. Some applications demand that wire adhere to SAE guidelines.

Cross-link wire has three main types based on the wall thickness of insulation. However, all three suit automotive applications requiring extreme cold and high heat conditions.

  • SXL: This is the wire with the thickest insulation and thus has high abrasion resistance. The wire is a preferred choice for applications requiring exposure to elements. Mostly, people like these wires for heavy applications like in engine compartments. Having thick insulation also makes it highly durable.
  • GXL: Though thinner than SXL, it is still good for under-the-hood applications. The wire is suitable for use in engine compartments of trailers and trucks. As its insulation is thinner than SXL, it is light in weight, less expensive, and more flexible.
  • TXL: It has extremely thin insulation, but it is still good for under-the-hood purposes. Its thin insulation makes it very flexible and easy to use. Also, it can slide through tight spaces and utilize less space.
Chassis wiring harness

Chassis wiring harness

High-voltage automotive cables and their insulation:

Apart from the low-voltage wires, you may also need high-voltage automotive wires, which can handle up to 600 volts. 

You may need such wires for the generator, inverter, car batteries, converter, etc.

SGT battery cable:

This is a very common cable found in most applications. You can use them in electrical projects and for battery replacements. The cable protects against acids, oils, and cracking.

It has polyvinyl chloride insulation that keeps the connection secure and reliable. This cost-effective cable also meets SAE specs J-1127 and can work in temperatures up to 80 degrees Celsius.

You can get this cable from the market in different sizes, ranging from 6-4/0 gauge. The variety in sizes makes this SGT cable suitable for different jobs.

SGX battery cable:

This premium category cable offers better heat protection than the former. 

The cable is suitable for applications having temperatures up to 125 degrees Celsius. 

It has XLPE (cross-linked polyethylene plastic) insulation that protects against coolant, alkalis, acid, abrasion, flames, oil, steering fluid, ethanol, and transmission fluid.

With so many protective features, it is best used in the engine compartment of buses, trucks, boats, tractors, or RVs. 

The high durability and reliability of this cable come at a higher cost than SGT cables.

Like SGT, you can get these cables in red and black in spool sizes of 25, 100, and 500 feet. 

This cable also adheres to the SAE specs J-1127 and fulfills the specifications of UL 558 and UL 583.


So, choose the type of wire insulation according to your application.

 Also, whether you are looking for a low-voltage or high-voltage automotive wiring harness, Cloom can meet the most demanding power requirements. 

We design cables with stable properties and easy installation features so you can install them in the most complex harnesses.

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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