Basic knowledge of integrated wiring

Characteristics of various cable sheaths

All along, the industry has been arguing about the characteristics of network data cable jackets, such as whether the jacket can meet the flame retardant or low smoke standards? Does it need to contain a high ignition point, flame resistance, but in a fire will release halogens of toxic gases? Network cabling professionals, the vast majority of network users, and even standards organizations in different regions have differences. With the advent of the era of integrated voice, data and images, multimedia broadband, and converged networks, network cabling will penetrate into thousands of households, and correctly understand the composition and characteristics of network data cable jackets. For future network construction The work and life of the user and the user are very important.

As for the selection and standards of network data cable jackets, North American and European standards organizations and manufacturers are as long as they are using UTP or FTP shielding products. At present, North America, South America, Asia-Pacific and China all adopt the North American-based cable fire protection standards UL and NEC (National Electrical Code), and parts of Europe adopt low-halogen or low-smoke halogen-free green environmental protection cable standards.

Controversy about halogen in skin

At present, the power and communication cables laid in most parts of the world contain halogens, and these cables emit toxic mist-like chemicals when they burn. In fires, halogen-containing cables generate acid gas, which damages workers' noses, mouths, and throats. The smoke also makes victims easily disoriented and difficult to escape from the scene of the fire.

Recognizing this potential hazard, some European countries have adopted halogen-free cables as the standard for power and communication cables. However, the National Electrical Code of the United States clearly stipulates that the communication network must use UTP (unshielded twisted pair) network cables of Category 5 or Category 6 with halogen-containing cladding. This is because, although the halogen-containing cable has important defects, the halogen itself has strong flame resistance and high ignition point. If the cable does not catch fire or is difficult to catch fire, it will not cause burning and emit toxic smoke. .

In fact, some fires are caused by overheating caused by the cable being energized for a long time. Halogen-free cables are more likely to cause fire because of their low ignition point, and halogen insulation can better prevent spontaneous ignition of cables. However, if the cable is already in a fire, the smoke it produces can cause life poisoning. These contradictions have been the focus of industry debate in the application of halogens.

Now, advocates of cable halogen, including companies such as the US Federal Corporation and Goodrich, dominate the technology. Opponents of halogens expect to be more able to persuade the NFPA (American Fire Protection Association) to revise the current standards, stop using halogens or allow the use of halogen-free cables in the ventilation of buildings.

This is not the first time that advocates of halogen-free cables have tried to modify the standard, but it has so far been unsuccessful. The main reason is that the spontaneous combustion of the cable in the trunk line channel makes it difficult for people to carry out regional fire control, resulting in a fire in the entire building, and the low ignition point is very easy to produce a fire source. Another main reason is that there is no evidence to prove that halogen-free cables can indeed save lives (because a large number of other decorative objects also contain halogens in the house).

According to the current U.S. Construction Act, the only halogen-free cable that can be legally installed is to place the cable in a metal conduit, which doubles the cost of the entire wiring system. Therefore, most European countries including France, Italy and the United Kingdom have turned to halogen cables. Among the communication cables in Europe, halogen-free cables currently account for about 25%, while in North America and most parts of the world, halogen cables account for more than 98% of the market. Cabling manufacturer Avaya has launched a full range of data cable solutions for users of different standards and different regions to meet the needs of different users.

The advantages of halogen-free

The characteristics of halogen-free are: low ignition point, easy to burn but low toxicity. The current international standards related to cables mainly focus on three issues: fire resistance (speed of cable burning), smoke density (how much visible smoke is produced), and toxicity (how much damage is caused to the human body). The US fire protection standard only covers the first two issues, but it is more widely and strictly used. To meet the US standard, halogen must be added to the polymer of the cable insulation layer. Its PVC cable contains chlorine, while FEP (Teflon (Teflon polytetrafluoroethylene) cable contains fluorine.

FEP has strong fire resistance, and can tolerate temperatures as high as 800 ° C or more before burning and disintegrating. It is several times higher than the maximum temperature of 150 ° C for halogen-free cables. FEP is also an efficient insulator. Therefore, FEP is very suitable for making cables that transmit high-speed data. It is the key factor for the widespread use of ultra-five UTP in ventilated places. In high-rise shafts and other ventilated places, FEP cables have largely replaced PVC cables. In some European countries, the standards are different. In order to comply with strict anti-toxicity regulations, cable manufacturers do not use halogens. Instead, metals are added to polyethylene and polylacene cable insulation. When heated, this cable only emits visible vapor with little toxicity. However, the fire resistance of this halogen-free cable is not as good as the halogen-containing cable, and its insulation layer will burn quickly. Therefore, halogen-free cables cannot meet the strict US fire protection standards. To meet the fire protection requirements at the ventilation and exhaust locations, excessive metal hydroxides have to be added, which affects the performance and technical requirements of the cables.

Cable toxicity battle

When the PVC cable burns, it emits hydrogen fluoride and dioxide gas, which are identified by Greenpeace as "scientifically known and toxic synthetic chemicals." When the FEP cable burns, it releases hydrogen fluoride, which is colorless and odorless, but more toxic than hydrogen chloride. Tests have shown that there is another dangerous gas in the FEP smoke. This super toxin has never been correctly recognized by humans, and research on it has now ceased, but some people think that this super toxin is only a product in experiments, and does not exist in reality.

The Anderson laboratory in Europe uses a method called the Pittsburgh test (this method is published by the University of Pittsburgh) to measure the toxicity of the cable sheath. In the test, a certain amount of insulating layer was burned, and the smoke was transmitted through the duct to the space where 4 white mice were located, and observed until 2 white mice died. At this time, the weight of the burning insulation layer is an LC50 toxic unit, which means that so many insulation layers will kill half of the tested animals when burning. Through this test, it was found that the toxicity of FEP cables is 1.5 times that of PVC cables and 5 times that of halogen-free cables. FEP supporters believe that this test is only academic, because the test environment is not a real fire scene, and when the temperature required to release those toxic gases in the building is reached, no matter who is, the temperature will be too high (800 ℃ ) And already dead.