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A detailed description of the classification, standards, and flame retardant grades of fire-resistant cables
Date：2021/12/21 Clicks：897
Fire-resistant cables have always been a very popular product type in the cable industry. Cablebao shares the classification of flame-retardant grades and related standards for fire-resistant cables for all colleagues in the industry.
Fireproof cable, that is, the sample is burned under the specified test conditions. After the test fire source is removed, the flame spreads only within a limited range, and the residual flame or residual burn can be extinguished by itself within a limited time. In the event of a fire It may be burned out and unable to operate, but it can prevent the spread of fire. In layman's terms, if a wire catches a fire, it can limit the combustion to a local area without spreading, and protect other equipment and avoid greater losses. At present, the cable industry is accustomed to fire Retardant, Low Smoke Halogen Free (LSOH) or Low Smoke Fume (LSF), Fire Resistant and other cables with certain fire resistance properties. Collectively referred to as fire-resistant cables. So what is the difference between these four types of fireproof cables? Let's first understand it briefly.
1. Classification of fireproof cables
Flame Retardant
The characteristic of flame-retardant cable is to delay the spread of flame along the cable so that the fire will not expand. Because of its low cost, it is a large number of cable varieties used in fire-resistant cables. Regardless of whether it is a single cable or a bundle laying, the spread of flame can be controlled within a certain range when the cable is burned, so it can avoid major disasters caused by the cable fire and prolonged combustion, thereby improving the fire protection level of the cable line .
Halogen-free low-smoke flame-retardant cable (LSOH)
The characteristics of halogen-free low-smoke cables are that they not only have excellent flame retardant properties, but also that the materials constituting the low-smoke and halogen-free cables are halogen-free, have low corrosiveness and toxicity during combustion, and produce a very small amount of smoke, thereby reducing the risk to the human body. , The damage of instruments and equipment is conducive to timely rescue in the event of a fire. Although halogen-free low-smoke flame-retardant cables have excellent flame retardancy, corrosion resistance and low smoke concentration, their mechanical and electrical properties are slightly worse than ordinary cables.
Low-halogen and low-smoke flame-retardant cable (LSF)
Low-halogen, low-smoke, flame-retardant cables have a hydrogen chloride release and smoke concentration index between flame-retardant cables and halogen-free low-smoke flame-retardant cables. Low halogen (Low Halogen) cable material will also contain halogen, but the content is lower. The characteristic of this kind of cable is that it not only has flame retardant properties, but also emits less smoke and hydrogen chloride during combustion. This kind of low-halogen, low-smoke flame-retardant cable is generally made of polyvinyl chloride (PVC) as the base material, and then processed with high-efficiency flame-retardant, HCL absorbent and smoke suppressant. Therefore, this flame-retardant material significantly improves the combustion performance of ordinary flame-retardant polyvinyl chloride materials.
Fire Resistant
Fire-resistant cables can maintain normal operation for a certain period of time under the condition of flame burning, and can maintain the integrity of the circuit (Circuit Intergrity). Fire-resistant and flame-retardant cables produce less acid fumes when they burn, and their fire-resistant and flame-retardant properties are greatly improved. Especially in the case of burning, accompanied by water spray and mechanical shock, the cable can still keep the line intact.
Second, the difference between flame-retardant cable and fire-resistant cable
It is easy for ordinary people to confuse the concept of flame-retardant cables and fire-resistant cables. Although flame-retardant cables have many advantages that are more suitable for chemical companies, such as low halogen, low-smoke and flame-retardant, in general, fire-resistant cables can replace flame-retardant cables. , And flame-retardant cables cannot replace fire-resistant cables.
The two principles are different. The flame-retardant principle of halogen-containing cables is based on the flame-retardant effect of halogens, and the flame-retardant principle of halogen-free cables is to extinguish the fire by reducing the temperature of the precipitated water. Fire-resistant cables rely on the fire resistance of the mica material in the refractory layer. The heat-resistant characteristics ensure that the cable works normally even in the event of a fire.
The structure and materials of the two are different. The basic structure of the flame-retardant cable is: the insulating layer adopts flame-retardant material; the sheath and outer sheath adopt flame-retardant material; the wrapping tape and filling adopt flame-retardant material.
The fire-resistant cable usually adds a fire-resistant layer between the conductor and the insulating layer. Therefore, theoretically, a fire-resistant layer can be added to the structure of the flame-retardant cable to form a flame-retardant and fire-resistant cable. This is not necessary. Because the fire-resistant layer of the fire-resistant cable is usually directly wrapped with multi-layer mica tape on the wire. It can withstand long-term burning, even if the high polymer at the place where the flame is applied is burned, it can ensure the normal operation of the line.
The main technical indicators related to the fire safety of the cable are the flame retardancy of the CO 2 cable, the density of the smoke and the toxicity of the gas. Based on the above factors, the cable flame retardant standard system includes IEC standards, UL standards, etc. Let us understand what important grade regulations are included.
3. Relevant standards for fire-resistant cables
1. IEC standard for fire-resistant cables
In order to evaluate the flame-retardant performance of cables, the International Electrotechnical Commission has formulated three IEC standards: IEC60332-1, IEC60332-2 and IEC60332-3. IEC60332-1 and IEC60332-2 are used to evaluate the flame retardant ability of a single cable when placed in an inclined and vertical position (corresponding to the standards of GB12666.3 and GB12666.4 in China). IEC60332-3 (corresponding to GB12666.5-90 in China) is used to assess the flame retardancy of bundled cables when they burn vertically. In contrast, the flame retardant requirements of bundled cables are much higher when they burn vertically.
IEC60332-1/BS4066-1 flame retardant rating (Flame Test On Single Vertical Insulated Wires/Cables)
This is the flame retardant standard for a single cable. The test stipulates that a 60cm long sample is vertically fixed in a metal box with an open front wall, and a propane burner with a flame length of 175mm is in contact with the cable at a 45-degree angle from a position 450mm away from the upper fixed end of the sample. If the burning damage part of the sample is not more than 50mm from the lower part of the fixed end, the test passes.
IEC60332-3/BS4066-3 flame retardant rating (Flame Test On BunchedWires/Cables)
This is the flame retardant standard for bundled cables. The test stipulates that a bundle of 3.5m long cable samples is fixed on a trapezoidal test frame with iron wires, and the number of samples is determined by the non-metallic materials required by different classifications. The sample is hung vertically on the back wall of the combustion furnace, and the air is introduced into the combustion furnace through the air inlet on the bottom plate. The propane plane burner is in contact with the sample with a flame at 750°C. The sample must not be ignited within 20 minutes of vertical combustion when the sample is forced to blow (air discharge 5m3/min, wind speed 0.9m/sec), and the cable spreads in the flame. It will extinguish itself within 2.5 meters. IEC60332 is divided into Class A, Class B, Class C and Class D to evaluate the flame retardant performance.
2. UL standard for fire-resistant cables
If any cable listed by UL has been tested and verified to meet a certain fire rating, the UL identification, fire rating and approval number can be printed on the cable.
Supercharged-CMP level (supply air combustion test/Steiner tunnel test Plenum FlameTest/Steiner TunnelTest)
This is the most demanding cable (Plenum Cable) in the UL fire protection standard. The applicable safety standard is UL910. The experiment stipulates that multiple samples should be laid on the horizontal air duct of the device and burned with an 87.9KW gas Bunsen burner (300,000BTU/Hr) 20 minutes. The eligibility criterion is that the flame cannot extend beyond 5 feet from the front end of the gas Bunsen burner. The maximum value of the optical density is 0.5, and the maximum value of the average density is 0.15. This kind of CMP cable is usually installed in the air return pressurization system used in ventilation ducts or air handling equipment, and is approved for use in Canada and the United States. FEP/PLENUM materials conforming to UL910 standard have better flame retardancy than low-smoke halogen-free materials conforming to IEC60332-1 and IEC60332-3 standards, and the concentration of smoke when burned is lower.
Mainline level-CMR level (Riser Flame Test)
This is a riser cable in the UL standard, and the applicable safety standard is UL1666. The experiment stipulates that multiple samples are laid on the simulated vertical shaft, and the specified 154.5KW gas Bunsen burner (527, 500BTU/Hr) is used for 30 minutes. The eligibility criterion is that the flame cannot spread to the upper part of a 12-foot-high room. There is no smoke density specification for trunk-level cables, and they are generally used for floor vertical and horizontal wiring.
Commercial Grade-CM Grade (Vertial Tray Flame Test)
This is a general purpose cable in the UL standard, and the applicable safety standard is UL1581. The experiment stipulates that a number of samples are laid on a vertical stand of 8 feet high, and burned with a prescribed 20KW band burner (70,000BTU/Hr) for 20 minutes. The qualification standard is that the flame cannot spread to the upper end of the cable and extinguish itself. UL1581 is similar to IEC60332-3C, except that the number of cables to be laid is different. Commercial-grade cables do not have smoke density specifications, and are generally only used for horizontal wiring on the same floor, and not for vertical wiring on the floor.
General level-CMG level (Vertial Tray Flame Test)
This is a General Purpose Cable in the UL standard, and the applicable safety standard is UL1581. The test conditions of commercial grade and general grade are similar, and they are both approved for use in Canada and the United States. There is no smoke density specification for general-purpose cables, and they are generally only used for horizontal wiring on the same floor, and not for vertical wiring on the floor.
Household level-CMX level (Vertial Wire Flame Test)
This is a Restricted Cable in the UL standard. The applicable safety standard is UL1581, VW-1. The experiment stipulates that the sample should be kept vertical, burned with the test burner (30,000 TU/Hr) for 15 seconds, then stopped for 15 seconds, and repeated 5 times. The qualification standard is that the residual flame should not exceed 60 seconds, the sample should not be burned by more than 25%, and the surgical cotton pad on the bottom should not be ignited by falling objects. UL1581-VW-1 is similar to IEC60332-1, except that the burning time is different. This level also has no smoke or toxicity regulations, and is only used in home or small office systems where a single cable is laid. This kind of cables should not be used in bundles, they must be sleeved. Smoke density, halogen content and toxicity level.
3. Other standards for fireproof cables
IEC60754-1/BS6425-1 Determination of halogen gas content (Emission Of Halogens)
This is the specification for the release concentration of hydrogen chloride (HCL) in the IEC and BS standards. Halogens contain fluorine (Florine), chlorine (Chlorine), bromine (Bromine), iodine (Iodine) and radioactive volatile element Astatine (Astatine), and the components are highly toxic. The experiment stipulates that when the combustion furnace is preheated to 800°C, a built-in 1.0g sample is pushed into the furnace, the HCL is dissolved into the water using the air discharge rate, and then the halogen acid content of the aqueous solution is measured. If the amount of halogen acid (HCL) released when the cable material is burned is less than 5mg/g, it can be called a halogen-free cable (LSOH). If the amount of halogen acid (HCL) released is greater than 5mg/g but less than 15mg/g, it can be It is called low halogen cable (LSF). It is worth noting that the IEC60754-1 method cannot be used to determine materials with HCL content less than 5 mg/g, that is, it cannot be determined whether it is "halogen-free". Need to determine whether it is completely halogen-free can be determined by the IEC60754-2 method.
IEC60754-2 gas acidity measurement (Corrosivity)
This is the IEC standard for the corrosiveness of combustion gas. This test measures the acidity of the halogen acid gas produced by the material during combustion. It is determined by the pH value and conductivity of the aqueous solution. The experiment stipulates that the combustion furnace is preheated to 800°C, a quartz tube with a built-in sample is pushed into the furnace, and the time is started at the same time. In the first 5 minutes of burning the sample, the pH value and electrical conductivity are measured every 1 minute, and every 5 minutes for the next 25 minutes. Generally, the PH value of halogen-free cable materials is greater than 4.3, and the conductivity is less than 10μs; the lower the PH value, the higher the acidity of the halogen acid gas of the material. It is worth noting that when the HCL content is greater than 2mg/g and less than 5mg/g (that is, when it meets the requirements of IEC60754-1), the pH value of its aqueous solution is also less than 4.3, that is, it does not meet the requirements of IEC60754-2.
IEC 61034-1/ASTM E662 (Emission of Smoke)
This is the smoke density specification in the IEC and ASTM standards. The experiment consisted of a 3m3 cube and a photometric system with a light source. The rectangular shape contained alcohol as the combustion source. A blower with a power of 10-15 m3/min ensures that the smoke is evenly distributed on a windshield to prevent flame vortexes on the groove. When the alcohol burns, the recorder connected to the optical power source records the amount of light attenuation. Smoke density is measured by light transmittance. If it can reach 60% light transmission value (Light Transmittance), the cable material will meet the low smoke standard. The higher the light transmittance, the less smoke the material emits when it burns.
ISO4589-2/BS2863 oxygen index (Oxygen Index LOI)
This is the specification for the oxygen index in the ISO and BS standards. It means that at room temperature, when the oxygen content of the air is greater than this oxygen index, the material will burn immediately. The higher the oxygen index value, the more flame-retardant the material. If the oxygen index of a material is 21%, it means that the material will automatically burn at normal room temperature. At normal room temperature, the oxygen content of the air is 21%. Generally, the oxygen index of flame-retardant cables is greater than 33%.
ISO4589-3/BS2782.1 Temperature Index (Temperature Index TI)
This is the temperature index specification in the ISO and BS standards. The oxygen index of the material will decrease as the temperature rises. When the temperature rises and the oxygen index of the material drops to 21%, the material will automatically burn, and the temperature will be reduced. It is called the temperature index. For example, the oxygen index of coal at room temperature is 50%, but when the temperature rises to 150°C, the oxygen index will drop to 21%, the material will burn immediately, and the temperature index of the material will be 150°C. Generally, the temperature index of flame-retardant cables is greater than 250°C.
NES713 Toxicity Index (Toxicity Index)
This is the British naval engineering NES standard for cable materials The toxicity specification of the gas produced during combustion. Toxicity refers to a property that causes damage to the structure of the organism or dysfunction. The toxicity index refers to the total toxicity of all gases produced when the material is burned. The experiment stipulates that when the combustion furnace is preheated to 800℃, the toxic substances contained in the cable material will be burned separately, and then the airflow rate is used to collect each toxic gas, and then the content of each toxic substance is calculated through chemical analysis. This index is based on The number indicates its toxicity. The greater the toxicity index, the higher the toxicity of the gas released by this material. Generally, the toxicity index of halogen-free cable materials is less than 5. It is worth noting that low-smoke halogen-free materials will also produce toxic CO when burned. If the materials contain P, N, and S, more toxic gases will be generated. Therefore, halogen-free cables cannot be called non-toxic cables. It is a low-toxic cable. Because CM, CMR and CMP cables need to pass strict UL fire protection standards, most of the cable materials used contain halogen. CM and CMR cables generally use polyvinyl chloride (PVC) as the base material, while PVC materials contain chlorine; CMP cables generally have special characteristics. Fluorine polytetrafluoroethylene (FEP) is the base material, and the FEP material contains fluorine. The toxicity of the gas produced by this kind of halogen-containing cables is several times greater than that of halogen-free cables. There are great hidden dangers in fire safety, which may cause most of the casualties at the fire scene to be suffocated by poisonous gas instead of being burned. .
With the continuous expansion of China's power industry, data communication industry, urban rail transit industry, automobile industry, shipbuilding and other industries, the demand for wires and cables will continue to grow rapidly. In the future, the wire and cable industry has huge development potential, and we fully understand The fire and flame retardant standards and grades of wires and cables are becoming more and more important for people in related industries.
With the continuous expansion of China's power industry, data communication industry, urban rail transit industry, automobile industry, shipbuilding and other industries, the demand for wires and cables will continue to grow rapidly. In the future, the wire and cable industry has huge development potential, and we fully understand The fire and flame retardant standards and grades of wires and cables are becoming more and more important for people in related industries.
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