Understanding the external characteristics of network data cables

I. Overview
The industry has been paying attention to the characteristics of the outer skin of network data cables, such as whether the outer skin can meet the flame retardant or low smoke standards, whether it has the characteristics of high burning points and fire resistance, however, with the latter feature, halide releases toxic gases during combustion. Network Cabling professionals and a large number of network users are even different from standard organizations in different regions. With the advent of the network age that integrates voice, data, and images, Multimedia broadband, and convergence, network cabling will go deep into thousands of households and understand the composition and characteristics of the outer cable cover of network data, it is important for future network builders and users to work and live.
Standard Organizations and manufacturers in North America and Europe have long been arguing over the selection and standards of network data cable skin. Currently, North America, South America, Asia Pacific, and China all adopt the North America-based cable fire prevention standard UL and NEC (National Electrical Code ), in some parts of Europe, low halogen or low smoke halogen-free green cable standards are adopted.
Ii. Halogen-free and halogen-free cables
Currently, power and communication cables laid in most parts of the world contain halogen. These cables emit toxic and mist chemicals during combustion. In the fire, halogen cables produce acidic gases, which damage people's noses, mouths, and throat. Smoke also makes victims easy to lose their way and it is difficult to escape from the fire. Recognizing this potential hazard, some European countries have used halogen-free cables as standards for power and communication cables. However, US National Electrical regulations clearly stipulate that the communication network must use cat5e or cat6 UTP (unshielded twisted pair wires) Network cables with halogen package layers. This is because although halogen-containing cables have important defects, halogen cables have strong fire resistance and high burning points. If the cables do not catch fire or are difficult to catch fire, they will not cause combustion, in this way, no toxic smoke is emitted.
In fact, some fires are caused by overheating caused by a long power-on period of the cable itself. Halogen-free cables are more likely to cause fire because of low burning points, while halogen insulation can better prevent spontaneous combustion of cables. However, if the cable is already in the fire, the smoke will cause life poisoning. These contradictions have always been the focus of debate in the industry.
The main representative companies that support halogen-containing cable applications include federated companies and Goodrich. Organizations opposed to halogen-containing cable applications are more expected to persuade NFPA (American Fire Prevention Association) to modify the current standards to stop using halogen-containing cables or allow halogen-containing cables to be used in ventilated buildings.
Halogen-free cable advocates have tried to modify standards, but none have been successful so far. The main reason is that the burning of Self-burning cables in the main trunk trough makes it difficult for people to control regional fire prevention, resulting in fire in the whole building, and low-burning points are prone to fire sources. Another major reason is that there is no evidence that halogen-free cables can save lives (because there are a large number of other decorations in the House that also contain halogen ).
According to the current U.S. Construction Act, the only legally installed halogen-free cable is to place the cable in a metal catheter, which doubles the cost of the entire wiring system. Therefore, most European countries, including France, Italy, and the UK, have switched to halogen cables. Currently, halogen-free cables account for about 25% of communication cables in Europe. In North America and most of the world, halogen cables exceed 98% of the market.
At present, the relevant international standards for cables are mainly concerned with three issues: Fire resistance (Cable burning speed), smoke density (How much visible smoke is produced) and toxic (the amount of damage to the human body ). The u. S. Fire standards only involve the first two issues, but they are more widely and strictly used. To meet u. S. Standards, halogen must be added to the polymer of the cable insulation layer, the PVC cable contains chlorine, while the Teflon cable contains fluorine. FEP has a strong fire resistance. It can endure temperatures above 800 ℃ before the smoke is dissolved. It is several times higher than the temperature of Halogen-free cables that can withstand 150 ℃, FEP is also an efficient insulator. Therefore, FEP is very suitable for creating cables that transmit high-speed data. It is a key factor to widely use cat5e UTP in ventilation. In high-rise shafts and other ventilated places, FEP cables have largely replaced PVC cables.
Standards in some European countries are different. In order to comply with strict anti-virus specifications, cable manufacturers do not use halogen, instead of adding metal to the polyethylene and polyene cable insulation layer. When heated, this cable emits only visible gases with low toxicity. However, this halogen-free cable does not provide better fireproof performance than halogen-containing cables, and its insulation will soon burn. Therefore, halogen-free cables do not comply with strict American fire prevention standards. To meet the fire prevention requirements of ventilation and ventilation levels, they have to add excessive metal hydroxide, thus affecting cable performance and technical requirements.
When the PVC cable is burned, hydrogen fluoride and dioxide gases are emitted, and when the FEP cable is burned, it releases a colorless, tasteless, but more toxic hydrogen fluoride than hydrogen chloride. Tests show that another hazardous gas exists in FEP smoke. The Anderson laboratory in Europe used a method called the Pittsburgh test (published by the University of Pittsburgh) to measure the toxicity of the outer cable skin. In the test, a certain amount of insulation was burned, and smoke was transmitted to the space where four rats were located through a catheter until two rats died. Through this test, we found that the toxicity of FEP cables is 1.5 times that of PVC cables and 5 times that of Halogen-free cables. FEP advocates believe that the test is academic because the test environment is not a real fire scene and the temperature needed to release toxic gases in buildings is met, no matter what the temperature is too high 800 ℃) and has long been dead.
2.1 Low halogen), the material that makes up the cable may contain halogen, but the content is Low. IEC60754-1: 1994 GB/T 17650.1-1998) method for the determination of HCI content. There is no indicator in the standard. It is recommended that HCI be less than or equal to 100 mg/g.
2.2 halogen-Free halogen), the material that makes up the cable does not contain halogen, that is, low corrosive, its combustion product is less corrosive. With IEC 60754-2: 19911997 correction), China is equivalent to the GB/T17650.2-1998 method, the index is PH ≥ 4.3, r conductivity) ≤ 10 ps/mm. Many foreign countries or companies set the halogen-free standard as HCI ≤ 5 mg/g, which is inappropriate for Chinese people. Because IEC 60754-l has clearly indicated that this method cannot be used to determine materials whose HCI content is less than 5 mg/g, it is impossible to determine "Halogen-free ". Secondly, when the HCI content is greater than 2 mg/g, the pH value of the aqueous solution is less than 4.3, which does not meet the requirements of IEC6 0754-2. In addition, some people think that the IEC index PH ≥ 4.3, while the German indicator PH ≥ 3.5, so the IEC requirement is higher than that of Germany. This is only a superficial phenomenon. In fact, the effects of the two are exactly the same.
2.3 Low smoke), less smoke generated when the cable is burned, that is, high light transmittance. The international standard for low smoke is light transmittance ≥ 60%. It must be pointed out that the low smoke model of the wire and cable made of the so-called Low Halogen and low smoke material based on PVC in China cannot meet the above requirements. Unless otherwise stated in the product standards, such as the indicator for reducing light transmittance and indicating that the indicator falls below the requirements of international or national standards, so as to avoid misunderstanding.
2.4 LOW toxicity), resulting in LOW gas toxicity when the cable material is burned. The IEC standards are still under consideration. At present, the British Naval Engineering standard NES713 is used, expressed by the toxicity index TI). For example, the toxicity index of insulation materials is required to be smaller than 3, and the toxicity index of jacket is less than 5. Some manufacturers in China say they can provide halogen-free, non-smoke, and low-toxicity cables. Halogen-free and low-smoke materials produce toxic CO during combustion. If the materials contain P, N, and S, more toxic gases are generated.
Iii. Flame Retardant and fire resistance of cable outer skin
Fireproof Flame proof) cables are generic names for cables with fireproof performance. They are generally divided into Flame retardant cables and refractory cables. From the fire safety and fire-saving, there are more and more requirements on the fire resistance of cables, such as: Flame Retardant Flame retardancy)-block, delay the spread of Flame along the cable, so that the fire does not expand. Fire resistance)-maintain a certain period of time in the case of flame burning, that is, keep the line integrity Circuit integrity ). The Research and Development of flame retardant and refractory cables in China began in 1982. After five years, many cable manufacturers have put into production and their products have been recognized by users.
3.1 flame retardant properties
The flame retardant should not be referred to as flame retardant. The flame retardant should be in line with the international flame retardant, because RETARDANT is a delay and prevention measure. According to IEC332, flame retardant can be divided into single and bundle. In order to evaluate the flame retardant performance of cables, the International Electrotechnical Commission has formulated three standards: IEC332-1, IEC332-2 and IEC332-3. IEC332-1 and IEC332-2 are used to assess the flame retardant capacity of a single cable according to the tilt and vertical layout of the National Standard corresponding to GB12666.3 and GB12666.4), IEC332-3 national standard corresponds to the GB12666.5-90) bundle vertical combustion, in contrast, the vertical bundle has a higher requirement on the flame retardant capability.
According to the standard of vertical combustion test of GB12666.5-90 bundle, flame retardant according to its capacity and test time outside the fire source spraying time) is divided into A, B, C class.
The sample cable capacity is calculated as follows:
V = n (S1-S2) limit 1000
N-cable sample number in formula;
S1-sample cable external section mm2 );
S2-sum of Metal Area in the sample cable mm2 );
V-Sample Capacity and litre/meter)
Bundle combustion is divided into flame retardant Class A, flame retardant Class B, and flame retardant Class C. Fire Retardant Class D in IEC's new proposal, applicable to wire and cable with an outer diameter of 12mm and below. The total volume of the non-metallic materials used is only 1/3 of that of class C, that is, L/m. It is required that the time in the fire is 20 min and the burning height is less than MB, which is the same as that in class C. This proposal is not yet approved by a vote. In addition, IEC 35mm2-2 requires that, in the case of A Class A test, if the samples are arranged at intervals with A conductor greater, it can be arranged at the end and expressed in AF/R. Or use a wide ladder m wide) All arranged in front of the ladder with AF), and use double sprinkler for fire. However, if a large cable is placed in front of a standard ladder, a single jet lamp is used for fire and still recorded as AF.
3.2 Fire Resistance
According to China's Standard GB 12666.6-90, the fire resistance is classified into Class A and Class B. The fire supply temperature of Class A is 950 ℃ ~ The fire supply temperature of Class B is 1000 ℃ to 750 ℃ ~ 800 deg C. According to the requirements of IEC-, it is equivalent to Class B of Chinese standards. However, in the standard IEC60331-1999 recently published by IEC, the heat supply temperature is still 750 ℃ ~ 800 ℃, and the suggestions for increasing the test temperature are still under consideration. Therefore, for example, when A new national standard is adopted, there is no distinction between Class A and Class B.
Mineral insulation MI) cables are different from organic insulation cables. Flame Retardant and fire resistance are one of their inherent characteristics. Therefore, MI cables are recommended for fire prevention. According to the recently published UK standard BS7629-1997 and BS6387-1994, the flame retardant properties of the refractory cable are required by a single vertical combustion test. Therefore, if our country will follow suit, when formulating standards, we can also uniformly stipulate that the flame retardant grade of the refractory cable is a single flame retardant, the flame retardant code can be omitted in the model of the refractory cable. Of course, if the user asks to increase the flame retardant grade, then put the flame retardant code in the model. The burning characteristics of cables are always the same, regardless of the individual characteristics of each component.(