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Fireproof Cable Technology Trends
May 15, 2018

With the increasing popularity of information systems, they have begun to enter various working environments and every household. The integrated wiring system has changed from a new invention 20 years ago to an information system transmission cable that can be seen everywhere in people's daily lives. When people can complete a highly stable and highly reliable integrated wiring system, whether the wiring system can resist external invasion and avoid external hazards becomes a new target that people pay attention to.


In modern society, people rely more and more on fire and are increasingly exposed to fire. Therefore, the fire safety of building materials, including integrated wiring systems, has become a concern.


External fire can destroy the integrated wiring system and cause transmission interruption. At the same time, the integrated wiring system will generate more or less harmful gas and smoke in the flame, and it may also help the fire gradually spread to other floors or other rooms.

According to the statistics of the fire department, about 85% of the deaths in the fire were caused by the poisonous gas that was poisoned by the fire, the suffocation of the diffused smoke, or the inability to escape because of invisible paths. In buildings, the number of integrated cabling cables exceeds the number of cables in a building. Therefore, the fire prevention of integrated cabling systems has become one of the key considerations for system performance.


In China, the main flame-retardant cables currently used are:


CM CM grade cable


CM grade cable is currently the most commonly used twisted pair flame retardant grade, and its test standard is UL 1581. In China, almost all conventional twisted pairs can meet the CM flame retardant test.

Therefore, the fire resistance characteristics of CM-grade twisted pairs are as follows:

The

◆ Will not ignite;

◆ Smoke will be emitted in the flame and flames may occur;

◆ The spread of flame along the cable is slow;

◆ When the external fire source is cut off, the flame on the cable will gradually extinguish.


As long as the CM grade cable meets the fire rating requirements, it does not consider the smoke density and toxicity (the smoke density and toxicity are not mentioned in UL 1581).

CM grade cables are mostly horizontal twisted pairs and are used in the wiring subsystem.

The jacket layer of CM grade cable is mostly PVC material, and the insulation layer is high density PE material. Its advantage is that the price is cheap, but the disadvantage is that the burning point is low, the normal working temperature is below 70°C, and when the temperature reaches 160°C or higher, the PVC material emits toxic halogen and smoke. If it unfortunately burns it, it will also release a lot of heat.

According to the specification of integrated wiring construction, twisted-pair cables should be laid in floors, ceilings and walls after wearing metal pipes and metal bridges. At this time, ordinary twisted pairs can be installed in any place where smoke and toxicity are not taken into consideration.


⊙ CMR grade cable


The CMR grade cable is one of the flame-retardant cables defined in the U.S. UL standard and is mainly used for the indoor vertical main section.

When the cable is placed vertically, the direction of the cable is consistent with the direction of the flame, and the number of cables is often more, and the fire potential may be relatively large. In this case, a cable with a higher flame retardant rating than the ordinary twisted pair cable should be used. In the U.S. UL standard, it is defined that CMR grade cables can be used for vertical trunk lines.

The test standard for CMR grade cables is UL 1666, which is mainly used for cables in the vertical trunk subsystem.

In Article 1.3 of UL 1666, it is clearly stated that "this standard does not study the toxicity of burning or decomposition products", and in the standard, there is no mention of the smoke density problem. From this, it can be assumed that the cable with the CMR class test certificate does not have smoke density data and toxicity test data. If you want to know the value of these two parameters, you need to find another standard to test.

The outer sheath layer of CMR material is a highly flame-retardant PVC material, and the insulation layer is a high-density PE material. CMR high flame-retardant material achieves the goal of non-combustible by increasing the ignition point (about 300°C) and flame retardancy of the twisted pair. In the event of a flame burning, it emits toxic halogenated gases and lead vapors. The halogenated gases rapidly absorb oxygen, extinguishing the fire and causing the cable to extinguish itself. Therefore, in the flame, once the CMR material decomposes, it will produce gas and smoke that are harmful to the human body. At the same time, when its gas is combined with water, it will form an acidic liquid that is corrosive to the equipment.

Similarly, CMR twisted pairs should also be laid in the shaft after passing through metal tubes and metal bridges.


⊙CMP cable


The test standard for CMP grade cables is mainly UL 910 in the United States. It is mainly used for cables laid directly in ventilated or forced-ventilated environments without the use of metal pipes in horizontal subsystems.


In UL 910, the test requirements for flame retardance and smoke density were clearly proposed. However, in Section 1.3, there is still the phrase “this standard does not study the toxicity of combustion or decomposition products”. It can be seen that high flame-retardant cables have been required to consider the smoke density in addition to the flame-retardant requirements, but still separate the toxicity.


The sheathing layer of CMP grade cable is made of fluorine material (such as: PTFE: polytetrafluoroethylene or FEP: fluorinated ethylene propylene). It has a high decomposition temperature (more than 400 degrees) and a high ignition point (above 800 degrees). It is not easy to burn when the fire is low, so it has better fire resistance than other organic materials. However, in the event that the CMP material burns, it will release a colorless, odorless, more toxic fluorine gas, which will turn into corrosive fluorine acid when it encounters water (including water vapor).


The cost of CMP materials is very high, and its selling price is much higher than that of ordinary CM grade cables. This is also one of the two major roadblocks (costs and toxicity) that people are facing in the popularization of CMP cables.


According to accepted theory, the flame-retardant effect of the CM grade cable after passing through the metal pipe is equal to or higher than that of the CMP grade cable, but this is at the expense of increasing the metal pipe and occupying more space in the building. Of course the metal The pipeline also has other protection functions.

The National Electrical Code (NEC) of the United States has a clear rule: The communications network must use non-shielded twisted pairs with halogen-containing materials. This is because halogen-containing cables have important environmental protection deficiencies, but halogens themselves are highly flame-resistant and have a high ignition temperature. If the cable does not catch fire at all or it is difficult to catch fire, it will not cause combustion and will not be emitted. Poisonous smoke.


The United States was the invention of an integrated wiring system. In the case of fire prevention, the United States had in the past demanded that weak cables should be laid in metal pipelines like strong cables for fire protection. With the development of materials technology, the United States began to allow the use of high-grade fire-resistant cables in the weak current system, without the use of metal pipelines for fire protection, but the premise is that: the fire resistance of the cables is required to reach the ordinary cable through the metal pipe. Equal fire rating. Therefore, a series of highly flame-retardant fire-resistant cables have been gradually formed.


The decomposition temperature of high flame retardant fireproof cables is much higher than that of ordinary PVC and PE materials. For example, a CMP-grade cable jacket using a fluorine material has a decomposition temperature of up to 400 degrees, whereas ordinary PVC materials have a decomposition temperature of only about 160 degrees. In this way, when the fire started, because the temperature on the cable has not reached the decomposition temperature (the current twisted pair does not spontaneously ignite), the high-flame-retardant cable will not release toxic gases and smoke, nor will it emit heat. Make people have more time to escape.


As the UL910 Steiner Tunnel Test (NFPA-262) shows, the use of fluorine-based cables as the jacket layer has the same low-flammability and low-smoke characteristics as iron metal pipes, which lays the foundation for CMP grade cables.


Fireproof cable development trend


The current integrated cabling manufacturers have already entered the road of global sales. The major integrated cabling manufacturers also have two series of high-flame-retardant cables and low-smoke halogen-free cables, and some manufacturers also meet the requirements of low-smoke and halogen-free. , And meet the high flame retardant requirements of the cable.

With the development of science and technology, the technology of the United States and Europe is constantly merging in the quarrel. For example, in Europe, the EN 50289-4-11 standard, which is more stringent than CMP, has been introduced, and CPD series high flame retardant standards suitable for various cables are being established. If high flame retardance is combined with low smoke and halogen free, then it is conceivable that : The cables of buildings in the future will not be easily decomposed, and even if they are decomposed, they will not emit a large amount of toxic gas and smoke. It should be said that this is already a dream goal in the field of integrated cabling.


In China, green environmental protection has become a problem that people have to consider. In addition, the manufacturing facilities for low-smoke and halogen-free cables are inexpensive and do not need to be equipped with special toxic gas treatment equipment. Therefore, the development of low-smoke and halogen-free technologies is far more advanced than high flame retardancy ( Such as: CMP, LCC) technology is developing faster.


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