The difference between flame retardant cable and fire resistant cable

When do you use a ZR cable? when do you use an NH cable? What is the difference between applications? Below Hooha engineer will discuss the structure, characteristics, and selection of flame-retardant cables and fire-resistant cables.

In recent years, in the global power system fire accidents, the proportion of power system power supply interruption due to the ignition of power cables has increased. Therefore, in power plants, substations and other places where there are a large number of electrical equipment and densely laid a large number of cables, flame-retardant cables are used to prevent the spread of fire. It is increasingly important to use fire-resistant cables to ensure uninterrupted power supply of important circuits. However, some electrical designers have unclear the concept of flame-retardant cables and fire-resistant cables and do not understand the structure and characteristics of the two, resulting in the inability to properly design and select these two cables according to the power supply requirements, and design agents or supervision on site. The two cable installations cannot be properly guided during work. Therefore, a comprehensive and correct understanding of flame retardant and fire resistant cables is the primary condition for the correct selection of them.

Flame retardant cable

The flame-retardant cable refers to the cable that is burned under the specified test conditions. After the test fire source is removed, the flame spreads only within the limited range, and the residual flame or residual burn can be self-extinguished within a limited time. Its fundamental characteristic is that it may be burnt out in the event of a fire and cannot operate, but it can prevent the spread of fire. In layman's terms, if the cable is in a fire, it can limit the combustion to a local extent, without spreading, and keep other equipment to avoid further losses.

1) Structural characteristics of the flame-retardant cable

The structure of the flame-retardant cable is basically the same as that of the ordinary cable, except that its insulating layer, sheath, the outer sheath and auxiliary materials (packing and filling) are all or partially made of flame retardant material.

2) Classification of flame retardant cables

According to the different flame retardant materials of cables, flame retardant cables are divided into two categories: halogen-containing flame-retardant cables and halogen-free low-smoke flame-retardant cables.

The insulating layer, the sheath, the outer sheath and the auxiliary materials (including and filling) of the halogen-containing flame-retardant cable are all or partially made of halogen-containing polyethylene (PVC) flame retardant material and thus have good flame retardant properties. However, when the cable is burned, a large amount of smoke and halogen acid gas will be released. The halogen acid gas is corrosive to the surrounding electrical equipment, and rescuers need to wear a gas mask to get close to the scene to extinguish the fire. When the cable burns, it will cause harm to surrounding electrical equipment and rescue personnel, which is not conducive to firefighting and rescue work, resulting in serious "secondary hazard". The insulating layer, sheath, outer sheath and auxiliary materials (band and filling) of the halogen-free low-smoke flame-retardant cable are all or partially made of halogen-free cross-linked polyethylene (XLPE) flame retardant material, which not only has Better flame retardant properties, and there is no halogen acid gas emission when the cable is burned, the amount of smoke generated by the cable is small, and the corrosive gas generated by the cable combustion is also a compromise between the flame retardancy of the cable and the reduction of the amount of halogen acid gas generated. The method developed a low-halogen and low-smoke flame-retardant cable. Its halogen content is about 1/3 of the halogen-containing flame-retardant cable. The amount of smoke is also close to the recognized "low smoke" level.

According to the provisions of the "Test Method for Wire and Cable Combustion", the flame-retardant cables assessed by the bundled combustion test method are classified into three categories: A, B, and C. Among them, the test conditions of the A-type cable are the most demanding, and the performance is better than that of the B and C types. The price is also the most expensive. In order to achieve the flame retardancy of the cable or improve the flame retardant grade of the cable, a new type of so-called "oxygen barrier layer" or "fire barrier layer" has been developed as a new type of fire-retardant tape (fire barrier) for filling or wrapping fire. The structure of the flame-retardant cable and this cable is called "oxygen (fire) layer" cable. The main principle is to add metal hydrate components to the materials, and also realize low-halogen low-smoke, halogen-free low-smoke and flame-retardant of cables. However, the so-called "oxygen barrier" and "fire barrier" are only a means to achieve flame-retardant cable. In the final analysis, it is also a flame retardant cable, and the highest flame retardant level that can be achieved is also Class A. Therefore, the flame retardant cable cannot be called an "oxygen barrier" cable, but only the "oxygen barrier" cable is a flame retardant cable.