Electrical cables: understand them and use them correctly

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Electrical cables: understand them and use them correctly

Electrical cables are divided into 2 categories according to voltage: low-voltage and high-voltage cables. Cables used in houses and buildings are classified as low-voltage cables.

These are the cables discussed in this article.   In Thailand, low-voltage cables must comply with Thai Industrial Standard TIS 11-2531 or TIS-11-2531 Under the standard, low-voltage cables come in many cross-sectional sizes, from small to large, and withstand voltages from 300 volts to 750 volts. Cables complying with TIS 11-2531 are classified by size, voltage rating and application as follows:  

1. IV ( IV cables  ) 
This type is a single-wire or single-core cable rated for   a voltage of 300 volts   It is used for wiring into residential buildings supplied with   system  1 phase  
and must not be used with   system 3 phase   at a voltage of 380 volts. Exposed wiring must be secured with insulating supports, or installed in a wiring channel in a dry location.
It must not be installed in buried conduits or buried directly.

2. VAF ( VAF cables)  
This cable type withstands a voltage of 300 volts and is available as single-core, twin-core and versions with a protective earth conductor.
Single-core cables are round, while cables with  2 cores or 3 cores are flat. In addition to conductor insulation, they have an outer sheath. Twin-core cables are commonly secured along walls with cable clips ( Clip) or installed in wiring channels.

They must not be buried directly. Underground installation requires a buried conduit protected against water ingress. They are used in ordinary homes and must not be used in 3 phase circuits at 380 volts either. (In a 3 phase system, circuits split off for use as 1 phase at 220 volts may use them.)

3. THW ( HW cables  )
These electrical cables withstand a voltage of 750 volts. They are single-core cables widely used, particularly in   industrial factories

because they are used in normal three-phase circuits. Each core consists of multiple copper conductors stranded into one larger core. They may be installed exposed with insulating supports, in wiring channels or in buried conduits protected against water ingress. They must not be buried directly.

4. NYY ( NYY cables)  
These are available as single-core and multicore cables; multicore versions are also round. This cable type withstands 750 volts and is widely used because it is designed to resist environmental conditions through an additional sheath. Single-core NYY cable has one insulation layer around its core and one sheath.

The sheath protects against physical damage. Multicore NYY cables may be described as having 3 layers of insulation. In fact, they have one insulation layer; the other two layers are sheaths. The inner sheath acts as a former ( Form) to hold the cores twisted together in a round shape. An additional outer sheath protects against physical damage. Multicore NYY cables are available with 2 cores and 4 cores according to the application. These cables have the two sheath layers described above.

NYY cables with 4 cores include a neutral conductor and are called NYY-N ( NYY-N) They contain 3 live conductors and one neutral conductor with a cross-sectional area approximately half that of a live conductor, making them suitable for 3 phase 4 Another cable type is NYY-ground ( NYY-G) It is available with 2 cores 3 cores and 4 cores, with a protective earth conductor ( Groud) included as an additional conductor, making it suitable for connection to electrical equipment that must be earthed. All types of NYY cable can be buried directly because their outer sheath provides resistance to environmental conditions.

5. VCT ( VCT cables)  
These are round cables available with 1 cores 2 cores 3 cores and 4 cores, with a voltage rating of 750 volts. Like NYY cables, they have insulation and a sheath, but each conductor consists of many fine copper strands forming one core. This makes them flexible and resistant to vibration.

They are suitable for wiring to machinery that vibrates during operation. Their general applications are similar to NYY cables. VCT cable is also available as VCT-ground ( VCT-G) which has 2 cores 3 cores and 4 cores and an additional protective earth conductor, making it suitable for use with   electrical equipment   that must be earthed. VCT cables may be buried directly.