Types of electrical cable sheaths, applications and how to choose

The electrical cable sheath is the outer protective layer that plays an important role in protecting the inner conductor from environmental impacts, ensuring the cable operates safely and efficiently. However, there are many different types of sheaths on the market such as PVC, XLPE, PE… So how to find the most suitable cable sheath for your project?

1. What is an electrical cable sheath?

An electrical cable sheath is the outermost layer of material that covers the electrical conductor, with the primary functions of insulating and protecting the conductor from environmental impacts such as heat, water, chemicals, and mechanical shocks. In addition, the sheath also acts to prevent the spread of fire, resist corrosion, and reduce electromagnetic interference.

2. Classification of electrical cable sheath types

Based on the constituent materials, we can divide electrical cable sheaths into many types as follows:

2.1 PVC (PolyVinyl Chloride) sheath

PVC is the most commonly used thermoplastic for sheathing. It has good mechanical strength, high insulation, and resistance to acids, bases and many other chemicals.

Advantages: Cheap, easy to process, flexible, durable enough, continuous operating temperature from -10ºC to 70ºC.
Disadvantages: Lower heat resistance compared to other plastics, often generates toxic gas when burning (HCl).
Applications: Used in most types of domestic and light industrial electrical cables.

2.2 PE (PolyEthylene) sheath

PE (Polyethylene) is a thermoplastic synthesized from the polymerization of ethylene (C2H4) under suitable pressure and temperature, widely used in the wire and cable industry.

Advantages: Good insulation, high tensile strength and elasticity, good impact resistance, corrosion resistance, operating temperature from -40°C to +70°C
Disadvantages: Higher cost than PVC, generates a lot of black smoke when burning.
Applications: Used for indoor cable sheaths, underground cables, telecommunications cables…

2.3 XLPE (Cross-linked PolyEthylene) sheath

XLPE is a special form of PE, formed by cross-linking PE molecules together. This process significantly improves material properties such as heat resistance, high voltage tolerance, and aging resistance.

Advantages: Continuous operating temperature up to 90°C, can withstand up to 250°C for a short time. Better insulation than regular PE, suitable for medium and high voltage cables. Good crack resistance, chemical and weather corrosion resistance.
Disadvantages: Higher cost than PE and PVC, more complex processing requirements.
Applications: XLPE sheaths are widely used for power cables and underground resistors, heat-resistant cables, fire-resistant cables…

2.4 HDPE (High Density PolyEthylene) sheath

HDPE is a type of PE with high density (0.941 – 0.965 g/cm³), therefore has higher crystalline structure and hardness compared to LDPE (Low Density Polyethylene – 0.910-0.925 g/cm³) and MDPE (Medium Density Polyethylene – 0.926-0.940 g/cm³).

Advantages: Better mechanical strength than other PE types, good impact and abrasion resistance. Continuous operating temperature up to 75°C. Good insulation and water resistance. UV resistant.
Disadvantages: Lower flexibility and heat resistance than XLPE, easy to harden and become brittle at low temperatures.
Applications: Due to its high hardness and durability, HDPE is often used for the outer sheath of telecommunications cables, fiber optic cables, and direct burial underground cables.

2.5 Halogen-free sheath (LSZH/LSOH)

This sheath is made from a mixture of polyolefin plastics, without containing halogen elements such as chlorine, fluorine, bromine. When burning, they usually do not generate toxic gases or fumes. This material is often denoted as LSZH (Low Smoke Zero Halogen) or HFFR (Halogen-Free and Flame Retardant)

Advantages: low smoke generation and very low toxic gas and no acid gas when a fire occurs, less corrosive to electrical and electronic equipment.
Disadvantages: Higher cost than regular PVC and PE.
Applications: Suitable for use in train stations, airports, hospitals, schools, public buildings, tunnels and subway networks…

2.6 Rubber sheath

Rubber sheaths are made from natural rubber, chloroprene rubber, chlorosulfonated polyethylene rubber or synthetic rubbers such as silicone rubber, EPR (Ethylene Propylene Rubber). Flexible, chemical resistant, heat resistant.

Advantages: Very flexible, abrasion resistant, resistant to low and high temperatures, does not spread fire.
Disadvantages: Rubber sheaths are often expensive due to material costs and more complex manufacturing processes.
Applications: Used in many industrial, residential and commercial applications

2.7 Other sheath types

In addition to the common plastics mentioned above, we can also make electrical cable sheaths from some other plastics such as:

PUR (PolyUrethane): Very flexible, abrasion resistant, oil resistant, UV resistant, flame retardant. Due to higher production costs than PVC, they are usually not used for outer cable sheaths except for special requirements
PP (PolyPropylene): PP is a flexible, quite tough polymer with water resistance and chemical corrosion resistance. PP is often chosen when special features are needed such as higher heat resistance, better chemical resistance, or higher flexibility in specific applications.
PAR (PolyAmide Resin): also known as nylon plastic, is a type of synthetic polymer with high strength, flexibility and abrasion resistance. PAR plastic is used as a sheath for some types of cables used where optimal mechanical strength, flexibility, chemical resistance, and heat resistance are required.

3. How to choose the right electrical cable sheath

When choosing a sheath for cables, the following main factors need to be considered:

3.1 Installation environment and working characteristics:

The installation environment is an important factor when choosing an electrical cable sheath, the following factors need to be considered:

For indoor cables, you can choose PVC sheaths with flame retardancy or LSZH if you want more safety in case of incidents.
For outdoor cables, choose XLPE, HDPE sheaths to avoid damage caused by sunlight, rain, wind, etc.
Wet or dry environment: For wet environments, choose sheaths with good waterproof ability such as PE, XLPE, PVC.
High or low temperature environment: Choose sheaths with good heat resistance such as XLPE, EPR, rubber if the ambient temperature is high. Conversely, with low temperatures, prioritize choosing PE, PP, PUR.
Environments with many corrosive chemicals, choose sheaths such as PP, PUR, EPR.
Explosive environments: Use fire-resistant sheaths such as LSZH/LSOH to limit smoke and toxic gases when burning

3.2 Safety requirements

When choosing an electrical cable sheath, it is necessary to pay attention to the following safety factors:

For projects with high requirements, such as hospitals, choose LSZH sheaths to avoid generating toxic smoke when a fire occurs.
Chemical corrosion resistance: If the environment has many corrosive chemicals, choose sheaths such as PP, PUR, EPR.

3.3 Durability and lifespan requirements

For important projects that require long-term operation, you should choose sheaths with high life expectancy such as XLPE, PAR.

3.4 Cost constraints

PVC sheath is the most economical choice if conditions allow, PE sheath is usually of medium level, XLPE, LSZH, PUR, PAR sheaths will be more expensive due to superior features.

3.5 Selection process

The process of selecting an electrical cable sheath is also relatively simple with the following 4 steps:

Step 1: Clearly identify the usage environment and safety requirements of the electrical system. List them in detail.

Step 2: Refer to the advantages and disadvantages of each type of sheath in part II to choose the 2-3 types that best match the requirements in step 1.

Step 3: Consider the cost and availability of the selected sheath types. You can consult reputable suppliers.

Step 4: Choose the optimal sheath type based on the above factors. If you are still hesitant, seek advice from experts.

In addition, it is necessary to comply with standards and regulations related to electrical safety when selecting and installing sheathed cables. Here are some notable standards:

USA: NEC (National Electrical Code) and UL (Underwriters Laboratories).
Europe: IEC (International Electrotechnical Commission) and BS (British Standard).
Vietnam: TCVN (Vietnam Standard).

4. Frequently Asked Questions (FAQ) about electrical cable sheaths

4.1 Which electrical cable sheath is best for residential use?

For ordinary residential houses, PVC sheath is the most popular choice because it is cheap and durable enough. If concerned about fire resistance, choose LSZH cables at a higher price.

4.2 How to check if an electrical cable sheath is damaged?

To accurately check if an electrical cable sheath is damaged, you need to pay attention to some easily recognizable characteristics such as:

For cables in use, observe the sheath surface for cracks, scratches, blisters or unusual discoloration.
For new cables, visually check the uniformity of the sheath, use your hands to feel if it is soft and flexible evenly.
The method of testing the insulation and durability of the cable sheath requires using specialized equipment.

4.3 Should I choose PVC or XLPE sheath for industrial electrical systems?

For low voltage circuits, using PVC is cheaper and easier to install. XLPE has a higher operating temperature (90ºC compared to 70ºC), better insulation and durability, suitable for industrial medium voltage cables.

4.4 Is LSZH sheath really safer in case of fire?

When burning, LSZH sheaths emit significantly less toxic gas and smoke than PVC or PE. However, LSZH can still ignite and generate heat. The most important factor to prevent the spread of fire is to quickly cut off the power when there is a fire. Ideally, use LSZH in combination with other fire prevention measures such as automatic fire alarm and extinguishing systems.

5. Conclusion

Through this article, we have gained an overview of electrical cable sheaths and their important role in protecting the safe and efficient operation of electrical systems. By classifying and analyzing the characteristics, advantages, and disadvantages of each type of sheath, the article has provided useful knowledge to help engineers and electricians make the right choices, contributing to protecting human safety and property during the operation of electrical systems.