Flame retardant cables are divided into ABC grades, and are flame retardant and fire resistant cable

It's the same, it's all graded ABCD

Medium cable** Flame retardant cable refers to a cable in which the sample is burned under the specified test conditions, and after the test ignition source is removed, the spread of the flame is only within a limited range, and the residual flame or residual burning can be extinguished by itself within a limited time. Its fundamental characteristics are:

In the event of a fire, it may be burned out and cannot be operated, but it can prevent the spread of fire. Generally speaking, in case of fire in the cable, the combustion can be limited to a local range, so as not to spread, save other various equipment, and avoid causing greater losses.

1 1 Structural characteristics of flame retardant cables.

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

1 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.

Among them, the insulation, sheath, outer sheath and auxiliary materials (tape and filling) of halogen-containing flame retardant cables are all or partially made of halogen-containing polyethylene (PVC) flame retardant materials, so they have good flame retardant properties. However, when the cable burns, it will release a large amount of smoke and halogen gas, which is corrosive to the surrounding electrical equipment, and rescuers need to wear gas masks to approach the scene to extinguish the fire. When the cable burns, it causes harm to the surrounding electrical equipment and rescuers, which is not conducive to fire fighting and rescue work, resulting in serious "secondary hazards".

The insulation, sheath, outer sheath and auxiliary materials (tape and filling) of halogen-free low-smoke flame retardant cable are all or partially halogen-free cross-linked polyethylene (XLPE) flame retardant materials, which not only have better flame retardant characteristics, but also have no halogen acid gas released when the cable is burned, and the smoke generation of the cable is also small, and the corrosive gas produced by cable combustion is also a compromise between cable flame retardancy and reducing the amount of halogen acid gas generation to develop a low-halogen and low-smoke flame retardant cable. Its halogen content is about 1 3 of halogen-containing flame retardant cables. The amount of smoke produced is also close to the recognized "low smoke" level.

According to the provisions of the "Wire and Cable Combustion Test Method", the flame retardant cables assessed by the bundle combustion test method are divided into A, B, and C3 categories, of which Class A cables have the most demanding test conditions, better performance than Class B and Class C, and the most expensive.

In order to realize the flame retardant of the cable or improve the flame retardant level of the cable, people have developed the flame retardant cable with a new structure such as the so-called "oxygen insulation layer" or "fire insulation layer" as a new structure such as filling or wrapping the fire insulation flame retardant tape (fire insulation layer), and this kind of cable is called "oxygen insulation (fire) layer" cable. The main principle is to add metal hydrate components to the material, and it can also achieve low halogen and low smoke, halogen-free and low smoke and flame retardant cables respectively. However, the so-called "oxygen barrier" and "fire barrier" are only a means to achieve cable flame retardancy, in the final analysis, it is still a flame retardant cable, and the highest flame retardant level it can achieve is also Class A.

Therefore, the flame retardant cable cannot be called an "oxygen barrier" cable, but can only be said to be a "oxygen barrier" cable.

Class C flame retardant cable refers to the ability to prevent the spread of flames even when subjected to extremely high temperatures, effectively preventing the spread of fire. It can stop the fire from spreading for more than 30 minutes, and it is a very safe cable material.

The common flame retardant cable grading standards are A, B, C, D, E, F six grades, and the characteristics of each grade are as follows:

Class A: It means that the cable has high flame retardancy, and the surface of the cable can block flame radiation, which can significantly reduce the spread of fire;

Class B: indicates that the cable is moderately flame retardant, and the flame surface can prevent diffusion, but the heat will be transferred to the inside of the cable;

Class C: It means that the cable has high flame retardancy, and the surface of the cable can prevent flame radiation, which can effectively prevent the spread of fire;

Grade D: It means that the cable has a certain flame retardancy, which can prevent the spread of fire for a period of time;

Grade E: It means that the cable has a certain degree of flame retardancy, which can prevent the spread of fire for more than ten minutes;

Grade F: means that the cable has low flame retardancy and can prevent the fire from spreading for more than tens of seconds;

It refers to the cable with flame retardant class C characteristics, which refers to the cable in which the sample is burned under the specified test conditions, and after the test ignition source is removed, the spread of the flame is only within the limited range of the search and grinding imitation, and the residual flame or residual burning can be extinguished within a limited time.

How to choose the flame retardant grade of the cable?

With the increasing popularity of social intelligence, cable wiring is like the human nervous system, extending to every corner of the building. Normally, we choose cables to consider "how many types of cables to use in this project, how many meters to use", but ignore the "fire and flame retardant requirements of cables", the result is that it is easy to cause disasters, causing huge losses to enterprises and individuals. So, how do we choose the flame retardant grade of the cable?

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1. The flame retardant grade of the cable needs to be selected according to the cable laying environment.

Cable laying is divided into indoor laying and outdoor laying, and indoor laying can be divided into open laying and dark laying; Outdoor laying can be divided into a variety of methods such as bridge frame, wall support, steel cable hanger, cable tunnel, cable trench, direct burial and so on.

Different cable laying environment and laying methods, the required cable flame retardant grade is different, such as: cable direct burial or separate pipe (metal, asbestos, cement pipe), or the cable is placed in a semi-closed bridge, trunking or special cable trench (with cover plate), in this environment, the cable is less likely to be invaded by external factors, even if it ignites due to narrow space and water occlusion, it is easy to self-extinguish, not easy to become a disaster, so we recommend using flame retardant class C cable or flame retardant class D cable;

Indoor open application (through the room and climbing the building), or dark passage (mezzanine, tunnel corridor), the trace fire is easy to reach the relatively large space after the fire and the air is easy to circulate, the flame retardant level should be moderately increased, it is recommended to choose flame retardant class B cable, or even flame retardant class A cable; When the cable laying environment is located in front of the furnace or in the chemical, petroleum and mine where the high temperature furnace is located or the flammable and explosive chemical, petroleum, and mine mines, it is necessary to deal with it strictly, and the flame retardant grade of the cable is rather high than low, and it is recommended to choose a flame-retardant class A cable, or a halogen-free low-smoke flame-retardant and fire-resistant class A cable.

2. The flame retardant grade of the cable needs to be selected according to the number of cable laying.

The number of cables is mainly the number of non-metallic materials of cables in the same space, which affects the flame retardant level of cables. The "same space" here refers to the space where the flame or heat can radiate unhindered to nearby wires and cables and ignite when a cable catches fire.

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3. The flame retardant grade of the cable needs to be selected according to the thickness of the cable.

The outer diameter of the cable is small and the heat absorption is small, easy to ignite, and the heat absorption of the cable with a large outer diameter is not suitable for ignition, so the flame retardant category should be strictly dealt with if the small one is mostly (diameter less than 20mm), on the contrary, if the large one is mostly (diameter more than 40mm) should be biased to the low level.

4. The flame retardant level of the cable needs to be determined according to the depth of fire hazard.

The cable of the large-scale and extra-large concentration place of the banking and financial center is easy to cause disasters, so the flame retardant level of the cable in this occasion should be high and strict, and it is recommended to choose a low-smoke halogen-free fire-resistant and flame-retardant cable.

However, there are many types of cables, various specifications and functions of cables, it is easy to confuse, if the project budget and arrangement, the performance and environment of the cable are not understood, it is easy to cause decision-making mistakes, which leads to a huge hidden danger of disaster.

Today, I will tell you what are the elements of the fire resistance and flame retardant grade of wires and cables that we should consider in the engineering design of the project?

01. Cable laying environment.

Regarding the laying of cables, different cables can adapt to different environments, and some special environments also need to use special cables. The laying environment of the cable determines the service life and safety of the cable to a large extent.

For example, in the environment of direct burial or separate pipe, non-flame retardant cables can be used. In the environment of semi-enclosed tray and trunking, the flame retardant grade of the cable can be selected, and it is recommended to choose flame retardant class C or class D.

The laying of the cable, the less affected by the environment, the safer the later use of the cable, once the fire occurs, it is easy to extinguish naturally due to the limitations of the space environment, and it is not easy to cause a big disaster.

In an environment where the space is relatively large or the air is relatively easy to circulate, the flame retardant grade of the cable should be adjusted and a higher flame retardant grade cable should be used. It is recommended to use Class B or Class A cable products.

There is also a situation that needs special attention, when the environment is in a high temperature or flammable and explosive environment, such as oil, mines and other environments, strict standards must be adopted, and flame retardant class A cables or low-smoke halogen-free flame retardant flame retardant class A must be used.

02. How many cables are laid.

The number of cables laid in the same environment can also affect the flame retardant rating of the cable, what is the reason for this? To put it simply, the greater the number of cables in the same environment, that is, in the same space, in the event of a fire, the heat generated by the flame or combustion will not be limited in any way, and it will radiate to the nearby cables and make it burn, which can easily make the fire expand. Therefore, the fire retardant rating needs to be adjusted.

In addition, it is not enough to adjust the fire retardant level, but it is also necessary to set up isolation measures such as isolation panels around the cables in the same space, so that in the event of a fire, they will not be affected by each other.

03. The thickness of the cable.

In the same environment, for example, in a laying pipe, the thickness (cross-sectional area) of the cable can also affect the flame retardant effect, which must also be taken into account. If the majority of thick cables are thick, the flame retardant grade can be C or D, and if the cables are relatively thin, they need to be adjusted to B or A.

The reason for this is that the smaller the cable, the smaller the heat absorption, which is easy to ignite and cause a fire, while the relatively thick cable, the greater the heat absorption, and the less likely it is to ignite.

04. Flame retardant and non-flame retardant cables should not be mixed in the same channel.

It is important to note that flame retardant cables and non-flame retardant cables are not suitable for laying in the same pipe. When laying cables, it is best to lay cables of the same grade together.

According to the test conditions specified by GB, flame retardant wires and cables are divided into four grades: A, B, C, and D. zra zrb zrc。

Flame retardant cable refers to the cable in which the sample is burned under the specified test conditions, and the spread of the flame is only within a limited range after the test ignition source is removed, and the residual flame or residual burning can be extinguished by itself within a limited time. The fundamental characteristic is that it may be burned out and cannot be operated in the event of a fire, but it can prevent the spread of fire.

In layman's terms, in case of fire in the wire, the burning can be limited to a local range, so as not to spread, save other equipment, and avoid greater losses.

Flame retardant cable A B C is classified according to the GB T18380-2008 standard, which is used to evaluate the ability of vertically installed bundled wires and cables or optical cables to inhibit the vertical spread of flames under specified conditions.

Flame retardant class A means: the cable is installed on the test steel ladder so that the total volume of the non-metallic material contained in the test is 7L m, the fire supply time is 40 minutes, after the cable combustion stops, wipe the sample, and the maximum carbonization range of the test shall not be higher than the bottom of the blowtorch.

Flame retardant class B means: the cable is installed on the test steel ladder to make the non-metallic materials contained in the test in the total volume, the fire supply time is 40 minutes, after the cable combustion stops, wipe the sample, and the maximum carbonization range of the test shall not be higher than the bottom of the blowtorch.

Flame retardant class C means: the cable is installed on the test steel ladder to make the total volume of the non-metallic materials contained in the test, the fire supply time is 20 minutes, after the cable combustion stops, wipe the sample, and the maximum carbonization range of the test shall not be higher than the bottom of the blowtorch.

Not only the difference in flame retardant time, but also the temperature, ignition point, combustion speed and other conveniences.

Flame retardant cables A B C D class is classified according to the GB T18380-2008 specification rules and is used to evaluate the ability of vertically installed bundled wire cables or fiber optic cables to suppress the vertical spread of flames under regular conditions:

Flame retardant class A means: the cable is installed on the experimental steel ladder to make the non-metallic material contained in the experiment in the total volume is 7L m, the fire supply time is 40 minutes, after the cable incineration is stopped, wipe the sample, and the maximum carbonization range of the measured sample shall not be higher than the bottom of the blowtorch for the occasion of assessing the volume content of high non-metallic materials.

Flame retardant class B means: the cable is installed on the experimental steel ladder to make the total volume of the non-metallic material contained in the experiment, the fire supply time is 40 minutes, after the cable incineration is suspended, wipe the sample, and the maximum carbonization range of the sample shall not be higher than the bottom of the blowtorch for the occasion of assessing the volume content of medium non-metallic materials.

Flame retardant class C means: the cable is installed on the experimental steel ladder to make the total volume of the non-metallic material contained in the experiment, the fire supply time is 20 minutes, after the cable incineration is suspended, wipe the sample, and the maximum carbonization range of the sample shall not be higher than the bottom of the blowtorch for the occasion of evaluating the volume content of low non-metallic materials.

Flame retardant class D means: the cable is installed on the experimental steel ladder to make the non-metallic material contained in the experiment in the total volume, the fire supply time is 20 minutes, after the cable incineration is suspended, wipe the sample, and the maximum carbonization range of the sample shall not be higher than the bottom of the blowtorch for the evaluation of the small cable with very low volume content of non-metallic materials.

Note: Flame retardant Class D is only applicable to small wires and cables or fiber optic cables with an outer diameter of 12mm and wires and cables with a nominal conductor cross-sectional area of 35mm.