What are the categories of flame retardant cables and what are their precautions?

According to the difference of cable flame retardant material, flame retardant cable is divided into halogen flame retardant cable and halogen free low smoke flame retardant cable two categories.

The halogen containing flame retardant cable insulation layer, sheath, outer protective layer and auxiliary materials (band and filling) all or part of the halogen containing polyethylene (PVC) flame retardant material, so it has good flame retardant characteristics. But in the cable combustion will release a large amount of smoke and halogen acid gas, halogen acid gas on the surrounding electrical equipment has corrosive harm, rescue personnel need to take gas masks to near the scene for fire fighting. When the cable is burning, it is harmful to the surrounding electrical equipment and rescue personnel, which is not conducive to fire fighting and rescue work, thus causing serious "two times" harm".

The insulation layer and sheath and the outer sheath and auxiliary materials and low smoke HFFR cable (bag and filling) in whole or in part is used in crosslinked polyethylene (XLPE) containing no halogen flame retardant, flame retardant properties has not only better, and in burning without halogen acid gas emitted smoke the amount of the cable is small, between the corrosive gases produced by the combustion of a cable or cable of flame retardant and reduce the amount of halogen acid gas to compromise the way developed low smoke and low halogen flame retardant cable. Its halogen content is about 1 / 3 of halogen flame retardant cable.  The smoking rate is also close to the recognized "low smoke" level.

According to the "cable combustion test method", the flame retardant cables tested by bundle combustion test method are divided into A, B and C3 categories, among which class a cable test conditions are the most demanding, performance is better than B, C class, and the most expensive.

For the realization of the cable flame or improve flame retardant cable level, people have developed the so-called "extruded oxygen barrier" or "fire" as the packing or wrapping fire retardant bag (fire insulation layer) the new structure of the flame retardant cable, and the cable is called "oxygen (fire) layer" cable. The main principle is to add metal hydrate components in the material, and also realize low halogen, low smoke, halogen free, low smoke and cable flame retardant. However, the so-called "oxygen separation layer" and "fire isolation layer" is only a means to achieve cable flame retardant, in the final analysis, it is also a flame-retardant cable, and the highest flame retardant level can also be class A. Therefore, the flame retardant cable can not be called "oxygen insulated layer" cable, but can only say "oxygen barrier" cable is a flame retardant cable.

Problems needing attention in selection of flame retardant cable

The designer should design, select and lay down the flame retardant cable according to the specific characteristics of the flame retardant cable, and pay attention to the following problems:

(1) the halogen containing flame retardant cable (including flame retardant cable, low smoke and low halogen flame retardant cable) in combustion will release the halogen acid is corrosive, greatly hinder the fire control work to delay the fire fighting time and exacerbate the spread of fire, so it should try to design low smoke HFFR cable in high population density in public places. Any flame retardant cable can be used in the less densely operated area.

(2) flame retardant cables are classified into A, B and C3, among which class a flame retardant cable is better than B and C, and the most expensive. Design personnel to provide order list should be marked flame retardant cable categories.

(3) the A, B and C categories of flame retardant cables can not be distinguished from the appearance. Only manufacturers can guarantee the supply. Therefore, the cable manufacturer should be carefully chosen in the design.

(4) compared with halogen containing flame-retardant cables, halogen free low smoke flame retardant cable has the advantages of low corrosion and low smoke, but the electrical performance and mechanical properties are obviously reduced. Therefore, halogen free low smoke flame retardant cable should have greater bending radius than halogen flame retardant cable in cable laying.

(5) in the design of cable laying, it is not suitable to lay the non flame retardant cable and flame retardant cable together, so it is not suitable to lay the flame retardant cables of different flame types in parallel.