In the process of creating the linear part of the power electrical wiring, it is advisable to use those types of cables that meet special fire safety requirements. In the household sector, among such products, VVGng-LS are most widely used. Next, we will try to answer the question of why such a picture has developed.
The need for increased attention to the fire-fighting properties of the cable
The need for special attention to the fire-fighting properties of the cable is due to the following two factors:
- widespread use of polyvinyl chloride (PVC) for the manufacture of insulation and sheathing of cable products manufactured until the end of the 90s. last century;
- a large number of cables in modern real estate objects.
As an insulation and sheathing material, PVC in its original form performs well its functions under normal conditions.
Unfortunately, none of us is immune from fires, and power wiring, if the rules for its creation and operation are violated, often becomes the cause of their occurrence. But in this situation, the unwanted properties of PVC begin to appear.
Under the influence of flame and high temperature on cable products, this material begins to decompose and releases at the same time:
- thick black smoke;
- chlorine and its compounds.
Chlorine is originally a poisonous gas. During the First World War, it was used as a chemical warfare agent. Thick black smoke leads to a loss of orientation in space, a person cannot leave the room, after literally two or three breaths he loses consciousness and dies.
Normative base for fire-fighting properties of cables
Since 2012, Russia has GOST 31565-2012, which defines the fire safety requirements for various cable products for use in buildings. The document has been repeatedly revised and in its modern form divides the entire set of cables into classes, and also indicates the preferred areas of use of products of each of the classes.
Separately, we point out that in terms of requirements for the fire-fighting properties of cable products, domestic standards are one of the most stringent in the world.
Achieving the required level of fire safety
The required level of fire safety of information and power cables is ensured by the use of sheath and insulation materials in the production process of the appropriate formulation.
For this, special additives are used that allow you to get:
- low smoke when exposed to flame - LS index (from the English. low smoke), and the smoke not only has a low optical density, but also ceases to be black, which allows you to leave the threatened room much faster;
- incombustibility - ng index, i.e. the cable under the influence of the flame continues to function normally for at least a predetermined time of tens of minutes.
These properties are confirmed by an official certificate, Figure 1. During the certification process, the cable must pass a series of tests that simulate typical fire conditions. The diagram of one of them is shown in Figure 2.
Of course, significant improvements in fire performance are not easy to achieve. It is bought by a certain rise in the price of products and a certain deterioration in its weight and dimensions. characteristics: due to the deterioration of the mechanical strength of the modified materials, the shell has to make it thicker.
Taking into account that human life and health are priceless, and if they are lost it is impossible to restore them, house wiring should be formed exclusively on VVGng-LS cables, Figure 3. Retaining all the best features and advantages of its prototype, both in terms of electrical characteristics and nomenclature, they reliably ensure compliance with modern fire safety standards, which becomes their main advantage.