Multiplex cables

Have you, as a newcomer to the electrical industry, ever heard of Multiplex cable? After reading this article, you will grasp comprehensive information about its structure, technical specifications and applications. This knowledge will help you select the most suitable product for your needs.

1. Overview of multiplex cable

1.1 What is multiplex cable?

Multiplex cable is a collective term for Duplex, Triplex, and Quadruplex cables. This terminology originates from Latin, with "multi" meaning many and "plex" meaning layers or components. It has been widely adopted by experts and electrical installation contractors to refer to this group of cables. Multiplex cable is constructed with copper or aluminum conductors (Grade 2 core, solid copper or aluminum wires stranded concentrically), insulated with PVC or XLPE. The cores are twisted together and used to connect low voltage lines to electrical consumption points such as households and factories.

1.2 Basic structure of multiplex cable

Multiplex cable consists of the following main layers:

• • Conductors: Copper or aluminum wires with the same nominal diameter, concentrically stranded into one or more layers depending on the application requirements.
  • Insulation layer: Covered with PVC or XLPE plastic.

The cores are twisted together to form Duplex (2 cores), Triplex (3 cores), or Quadruplex (4 cores) cables.  

2. Classification of multiplex cable

2.1 Duplex cable

Duplex cable is a twisted pair cable with a structure of 2 conductors. The conductors are made of copper or aluminum, insulated with PVC (gray and black) or XLPE. Applicable standards and technical specifications

• • Standards: IEC 60228/ TCVN 6612; IEC 60502-1/ TCVN 5935-1; IEC 60227; TCVN 6610-2; TCVN 5064.
  • Rated voltage (Uo/U): 450/750V or 0.6/1kV.
  • 50Hz test voltage for 5 minutes: 2.5kV (450/750V) or 3.5kV (0.6/1kV).
  • Max. conductor temperature in normal operation: 70ºC (PVC) and 90ºC (XLPE).
  • Max. conductor temperature in short-circuit for 5s max duration: 160ºC (PVC) and 250ºC (XLPE).

Applications   Duplex cable is commonly used to supply power to household appliances such as air conditioners, fans, lighting systems, etc. With its compact design and high flexibility, this type of cable is not only easy to install but also convenient to transport. Especially, the high-quality sheath of Duplex cable acts as an effective protective shield, ensuring the inner cores are safe from environmental impacts such as moisture, abrasion, and fire hazards.

2.2 Triplex Cable

Triplex cable is a twisted cable with a structure of 3 conductors. The conductors are made of copper or aluminum, insulated with PVC (red, yellow, blue) or XLPE. Applicable standards and technical specifications

• • Standards: IEC 60228/ TCVN 6612; IEC 60227/ TCVN 6610.
  • Rated voltage (Uo/U): 0.6/1kV.
  • 50Hz test voltage for 5 minutes: 3.5kV (0.6/1kV).
  • Max. conductor temperature in normal operation: 70ºC (PVC) and 90ºC (XLPE).
  • Max. conductor temperature in short-circuit for 5s max duration: 160ºC (PVC) and 250ºC (XLPE).

Applications Used for power distribution systems, fixed installation, connecting distribution lines to a junction box (commonly known as a four-pillar box) located at the front of each household or factory.

2.3 Quadruplex cable

Quadruplex cable is a twisted cable with a structure of 4 conductors. The conductors are made of copper or aluminum, insulated with PVC (red, yellow, blue, black) or XLPE. Applicable standards and technical specifications

• • Standards: IEC 60228/ TCVN 6612; IEC 60502-1/ TCVN 5935-1; TCVN 5064; IEC 60227.
  • Rated voltage (Uo/U): 450/750V or 0.6/1kV.
  • 50Hz test voltage for 5 minutes: 2.5kV (450/750V) or 3.5kV (0.6/1kV).
  • Max. conductor temperature in normal operation: 70ºC (PVC) and 90ºC (XLPE).
  • Max. conductor temperature in short-circuit for 5s max duration: 160ºC (PVC) and 250ºC (XLPE).

Applications Used for power distribution systems, fixed installation, connecting distribution lines to a junction box (commonly known as a four-pillar box) located at the front of each household or factory.  

3. Guidelines for buying multiplex cable

Depending on your usage needs or project requirements, you should choose the appropriate type of duplex, triplex or quadruplex cable. When selecting, pay attention to the following criteria:

3.1 Check technical specifications

Calculate Power Calculate the power to determine the consumption level of electrical devices in your home or project. Record the power (W) of each device and calculate the total. For example: If you have 10 LED bulbs (10W each), 1 air conditioner (1200W), and 1 refrigerator (200W), the total power will be: P= (10×10)+1200+200 = 1300W Determine Rated Current This is the maximum current that the cable can safely and continuously withstand over a long period of time. If the current exceeds the rated value, the cable will be overloaded, generating a large amount of heat, which can damage or cause the cable to catch fire. The rated current also depends on environmental conditions (air temperature, soil, installation depth, etc.). Therefore, you must choose a cable with a conductor cross-section and installation conditions that are suitable. The formula for calculating single-phase rated current is: I = P/U Where I is the current (A), P is the power (W), and U is the voltage (V). For example, if you use 220V voltage, the calculation formula will be: I = P/U = 1300/200 = 5.91A The formula for calculating three-phase rated current is: I = P/ (√3 x U x cosϕ x efficiency)

• • I: Rated current (A)
  • P: Power consumption (W or kW)
  • U: Voltage (V)
  • cosϕ: Power factor (usually from 0 to 1)

Voltage drop The voltage drop should not exceed 2.5% of the rated voltage (e.g. 5.5V for 220V single phase, 9.5V for 380V three phase). The voltage drop depends on the current, cable length, power factor and cable resistance. If the voltage drop is too large, choose a cable with a larger cross-section.

• • The formula for calculating the voltage drop in single-phase power: Vdrop=(2×I×L×R)/1000​
  • The formula for calculating the voltage drop in three-phase power: Vdrop=1.732×I×L×R)/1000​

Where L is the cable length (m), R is the cable resistance (Ω/km), I is the permissible current (A).

3.2 Choose the right type of cable

Cable cross-section:

• • Based on the calculated current, you can choose the appropriate cable cross-section. Commonly, Multiplex cables have cross-sections such as 4mm², 6mm², 10mm², 16mm², 25mm², 35mm²...
  • Refer to the cable cross-section lookup table to determine the appropriate cable type for your current.

Conductor material:

• • Copper: Better conductivity, but higher price.
  • Aluminum: Lighter and cheaper but has lower conductivity. Suitable for applications that do not require high performance.

Insulation: Choose the appropriate type of insulation for the installation environment:

• • PVC: Common, good heat resistance but cannot be used long-term in harsh environments.
  • XLPE: Better heat and mechanical impact resistance, suitable for use in environments with high durability requirements.

3.3 Choose a reputable supplier

Choose manufacturers with a reputable brand in the market, achieving quality certifications such as ISO or QUACERT, meeting domestic and international standards such as TCVN, IEC... to ensure quality and safety during construction and use. You can search for reviews from consumers on forums, e-commerce sites or social media pages to learn more about product quality and customer service.

3.4 Check warranty and after-sales service

Ensure that the product you buy must come with a clear warranty policy, usually from 1 to 5 years depending on the manufacturer. Check if the supplier or manufacturer provides technical support during installation and use. This is very important if you encounter problems during installation or use.

4. Frequently asked questions (FAQ)

4.1 Can multiplex cable withstand impacts from harsh environments?

If you install cables in harsh environments, you should choose multiplex cables with XLPE insulation. This is a type of plastic with high durability, heat resistance, and good mechanical strength, making it more suitable for use in harsh environments than PVC plastic.

4.2 What is the average lifespan of multiplex cable?

Multiplex cable does not have a specific lifespan because it also depends on factors such as:

• • Whether the multiplex cable is manufactured in compliance with production standards and quality. If there are deviations, it will also reduce the cable's lifespan.
  • If the cable size is not suitable for the expected load, frequent overloading will cause overheating, degrading the insulation and sheath, leading to premature failure.
  • Design and installation conditions that are prone to moisture, water, or chemical penetration into the cable will also greatly affect the cable's lifespan.

5. Conclusion

Multiplex cable is a term that encompasses Duplex, Triplex, and Quadruplex cables. This type of cable plays an important role in the construction and operation of modern electrical systems. Understanding the structure, properties, and selection methods will help electrical technicians, students, or engineers new to the electrical industry choose the right cable type, optimize costs, and ensure safety during installation and use. When choosing to buy Multiplex cable, always prioritize quality and safety. You can consult experts if necessary to make the right choices.