Analysis of external characteristics of network data cable

I. Overview

The industry has been concerned about the characteristics of network data cable skins, such as whether the skin can meet the standard of flame retardant or low smoke, the presence of a high ignition point, fire resistance, and a halogen with the latter characteristic that releases poisonous gas in the combustion. Network wiring professionals and the vast number of network users even in different regions of the standard organizations, there are differences. With integrated voice, data and images as one, multimedia broadband, integrated network era, network cabling will be more in-depth households, the correct understanding of the composition of network data cable and its characteristics, for the future of the network builders and users of the work and life are very important.

For the selection and standard of the network data cable, the standard organizations and manufacturers in North America and Europe are just as they have been arguing for a long time about using UTP or using FTP shielding products. At present, North America, South America, Asia Pacific and China are based on North America's cable Fire standards UL and NEC (National Electrical Code), parts of Europe, the use of low halogen or low smoke halogen-free green cable standards.

Two. Halogen and halogen-free properties of wire and cable skins

In most parts of the world, electricity and telecommunications cables are currently installed with halogen, which emits poisonous, foggy chemicals when burned. In the fire, the halogen cable will produce acidic gas, damage the nose, mouth and throat, smoke also makes the victim easily disoriented, difficult to escape from the fire scene. Recognizing this potential danger, some European countries have used halogen-free cables as a standard for power and communications cables. However, the National Electrical Regulations expressly stipulate that the communication network must use a five-class or six-type UTP (unshielded twisted pair) network cable with halogen-containing cladding. This is because halogen-containing cable, although it has important defects, but the halogen itself has a strong fire resistance and high ignition point, if the cable is not burning or difficult to catch fire, then it will not cause combustion, thus will not emit poisonous smoke.

In fact, some fires are caused by overheating because the cable itself is energized longer. Halogen-free cable because of low ignition point, so more likely to cause fire, and halogen insulating layer can better prevent the electric cable spontaneous combustion. However, if the cable is already in the fire, then the smoke produced by it will cause life poisoning. These contradictions in the application of halogen has been the focus of the industry controversy. (Computer science)

The main representative companies that support the application of halogen cables are the United States federal and Goodrich companies. Anti-halogen cable applications are expected to be more able to persuade the NFPA (American Fire Society) to revise current standards, discontinue the use of halogen-containing cables or allow the use of halogen-containing cables in the ventilation of buildings.

Halogen-free cable advocates try to revise the standard, but so far have not succeeded. The main reason is that the channeling of the spontaneous combustion of the main line groove inside cable is not easy to carry out regional fire control, which causes the fire of the whole building, and low ignition point is very easy to produce ignition source. Another major reason is that there is no evidence to prove that halogen-free cables can save lives (because there are a large number of other decorations and halogen in the house).

Under the current U.S. Construction Act, the only legally installed halogen-free cable is to place the cable in a metal conduit, which doubles the cost of the entire wiring system. As a result, most European countries, including France, Italy and the United Kingdom, have switched to the use of halogen cables. In Europe's communications cables, halogen-free cable currently accounts for about 25% of the proportion, while in North America and most parts of the world, halogen cable is more than 98% of the market.

At present, the relevant international standards related to cable are mainly concerned about three issues: fire resistance (the speed of the cable burning), smoke density (the number of visible smoke) and toxic (how much damage to the human body). The U.S. Fire safety standards only cover the first two issues, but it is more extensive and stringent use, to meet the United States standards must be added to the cable insulating layer of the polymer, its PVC cable contains chlorine, and FEP (Teflon Teflon PTFE) cable contains fluorine. FEP has a strong fire resistance, can endure up to 800 ℃ before burning smoke disintegration of temperature, it than the usual halogen-free cable maximum can withstand 150 ℃ temperature is several times higher, and FEP is an efficient insulator. Therefore, FEP is very suitable for the production of high-speed data transmission cable, is currently widely used in the ventilation of the five-type UTP key factors. In high-rise shafts and other ventilated places, FEP cables have been replaced by a large number of PVC cables.

In some European countries, the standard is different, in order to comply with strict toxicity regulation, cable manufacturers do not use halogen, replaced by metal to polyethylene and poly-butadiene cable insulation layer. When heated, this cable only emits a small toxic visible gas. However, the halogen-free cable is less fireproof than a halogen cable, and its insulating layer will soon burn. Therefore, halogen-free cable can not meet the stringent U.S. fire standards, to achieve ventilation and exhaust at the level of fire requirements, you have to add too much metal hydroxide, which affect the cable performance and technical requirements.

When the PVC cable burns, it emits hydrogen fluoride and two oxide gas, and when the FEP cable burns, it releases a colorless, tasteless, but more toxic hydrogen fluoride than hydrogen chloride. Tests have shown that there is another dangerous gas in the FEP smog. The Anderson Laboratory in Europe used the method known as the Pittsburg Test (which was published by Pittsburg University) to measure the toxicity of the cable's skin. In the test, a certain amount of insulating layer was burned, and the smoke was transported through the catheter to the space of 4 mice, and 2 mice were observed to die. Through this test, it was found that the FEP cable is 1.5 times times the toxicity of PVC cable, is 5 times times the halogen-free cable. FEP supporters argue that the test is academic, because the test environment is not a real fire scene, and when the temperature needed to release the poisonous gas in the building is too high (800 ℃), it will die.

2.1 Halogen (Low halogen), the material that forms the cable can contain halogens, but the content is low. The HCI content was determined by iec60754-1:1994 (GB/t 17650.1-1998) method. No index in the standard, suggest hci≤100 mg/g.

2.2 Without Halogen (free halogen), the material that makes up the cable does not contain halogen, namely low corrosivity, the corrosivity of its combustion product is low. With IEC 60754-2:1991 (1997 revision), China's equivalent adopted GB for gb/t17650.2-1998 method determination, the index is ph≥4.3,r (conductivity) ≤10ps/mm. Many foreign countries or companies to the halogen-free standard as hci≤5mg/g, the Chinese have also been emulated, this is not appropriate. Because the IEC 60754-l has clearly pointed out that this method can not be used to determine the content of HCI is less than 5mg/g, that is, can not determine "halogen-free." Secondly, when the HCI content is >2mg/g, the ph value of the aqueous solution is less than 4.3, which is not in conformity with the IEC6 0754-2 requirement. In addition, some people think that the IEC set of indicators ph≥4.3, and Germany's target is ph≥3.5, so the IEC requirements than Germany. It's just a superficial phenomenon. In fact, the effect of the two is exactly the same.

2.3 Smoke (low smoke), when the cable burning less smoke, that is, high transmittance. Low smoke of the international standard requirements for light transmittance ≥ 60%. It must be pointed out that the so-called low halogen and low smoke materials made of PVC based on the wire and cable, its low smoke can not achieve the above requirements, should not use the model of low smoke. Unless otherwise stated in the product standards, such as the reduction of transmittance indicators, and indicate that this indicator is lower than the requirements of international standards or national standards, so as to avoid user misunderstanding.

2.4 Low toxicity (toxicity), the gas is less toxic when the cable material burns. The standard IEC is still under consideration. At present, the use of more is the British Navy Engineering standard NES713, using toxicity index (TI), such as the requirements of insulation material toxicity index is less than 3, sheath toxicity index is less than 5. Some domestic manufacturers said that can provide halogen-free, low smoke, low toxicity cable. Because of halogen-free, low smoke materials will produce toxic co, such as the material contains P, N, S, then generate more toxic gas.

Three. Flame retardant and fire resistance characteristics of cable sheath

Fire Protection (Flame proof) cable is a general term of fire performance cable, usually divided into fire-retardant cable and fire-resistant cable two categories. From fire safety and fire Rescue, the requirements of the cable fire performance are more and more, for example: Flame retardant (Flame retardancy)-block, delay the flame along the cable spread, so that the fire does not expand. Fire-resistant (Fire resistance)-to maintain the integrity of the line (circuit integrity) in the case of a flame combustion that allows for a certain period of operation. The research and development of fire-retardant and fire-resistant cables in China began in 1982. After 5 years, many cable manufacturers have been put into production, their products have been recognized by users.

3.1 Flame-Retardant Properties

Flame retardant is not known as nonflammable, flame retardant and international general FLAME retardant suitable, because retardant is the meaning of delay, stop. According to the IEC332, the flame retardant has Tangen into a bundle of points. In order to evaluate the flame retardancy of cable, the International Electrotechnical Commission has set up three standards of iec332-1, Iec332-2 and iec332-3 respectively. Iec332-1 and iec332-2 are respectively used to assess the flame retardancy of a single cable by tilting and vertical distribution (GB corresponds to GB12666.3 and GB12666.4), iec332-3 (GB corresponds to gb12666.5-90) beam vertical combustion, in contrast to the beam perpendicular to the flame retardant capacity requirements are much high.

According to the standard of gb12666.5-90 beam vertical combustion test, the flame retardant according to its capacity and test time (external fire ignition time) of the length of a, B, c three categories.

The calculation method of the specimen cable capacity is as follows:

V=n (S1-S2) ÷1000

The root number of n-cable specimen in type;

s1-Sample Cable outer section (MM2);

The sum of the metal area of the s2-sample cable (mm2);

Sum of V-sample capacity (L/m)

Bundles combustion because of flame retardant a, flame retardant type B, flame retardant C-Class. The Flame retardant Class D in the new IEC proposal is applicable to wire and cable with an outside diameter of 12mm and below. The total volume of non-metallic materials used in the samples is only 1/3 of the C class, i.e. 0.5l/m. Requirements in the fire time of 20min and scorch height less than 2.5m is the same as the C class. Since the proposal has yet to be voted on. In addition, IEC 332-3 has a provision, that is, when doing a Class A test, if the sample interval arrangement (with a core conductor larger than 35mm2 occasions) in front of the standard ladder, can be arranged in the back, and the AF/R said. or using a wide-type ladder (0.8m wide) all lined up in front of the ladder (with AF), and with a double torch for fire. However, if the large cable is in front of the standard ladder, then use a single torch for the fire, still recorded as AF.

3.2 Fire Resistance characteristics

According to China's standard GB 12666.6-90, fire resistance is divided into Class A and class B two levels. The fire temperature of Class A is 750℃~800℃ for the 950℃~1000℃,b type. According to IEC 331-1970 standards, the equivalent of China's standard class B. However, in the recently published IEC standard iec60331-1999, the supply of fire temperature is still 750℃~800℃, and the proposal to improve the test temperature is still under consideration. Therefore, if the same use of the preparation of new national standards, fire resistance grade is not a Class B distinction.

Mineral insulated (MI) cables are different from organic insulated cables, flame retardant and fire resistance is one of its inherent characteristics, therefore, in the need for fire-resistant places, can be recommended to choose the MI cable. Flame retardant rating of fire-resistant cables According to the newly published British Standard bs7629-1997 and bs6387-1994, the flame retardant properties of the fire-resistant cable are required to be reported by the vertical combustion test. Therefore, if our country to emulate, in the formulation of standards can also be uniform requirements of fire-resistant cable flame retardant grade for a single root flame retardant, the type of fire-resistant cable can be the code of fire-retardant to omit. Of course, such as user requirements to improve the flame retardant grade, and then in the model to intervene in the flame retardant code. The burning characteristics of cable are all the time, regardless of the individual characteristics of each component.