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Standards and grades of flame-retardant cables

Cables involving fire safety The main technical indicators are the flame retardancy of CO2 cables, the density of smoke and the toxicity of the gas. American fire protection standards focus more on the first two issues, but Europe and the United States have completely different views on fire safety. The traditional concept in the United States believes that the root cause of fires lies in the generation of carbon monoxide (CO) poisonous gas and the subsequent heat release when CO is converted into CO2 during the combustion process. Therefore, controlling the heat release during the combustion process can reduce the hazards of fires. European tradition has long been convinced that the amount of halogen acid (HCL) released during combustion, gas corrosiveness, smoke concentration and gas toxicity are the main factors that determine whether people can safely escape from the fire scene.

IEC flame retardant grade

In order to evaluate the flame retardant performance of cables, the International Electrotechnical Commission has formulated three 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 laid obliquely and vertically (domestic corresponding standards GB12666.3 and GB12666.4). IEC60332-3 (domestic equivalent of GB12666.5-90) is used to evaluate the flame retardant ability of bundled cables when they are burned vertically. In comparison, the requirements for flame retardant ability of bundled cables when they are burned vertically are much higher.

◎ IEC60332-1/BS4066-1 flame retardant level (Flame Test On Single Vertical Insulated Wires/Cables)

This is the rating of a single cable Flame retardant standards. The test stipulates that a 60cm long specimen is vertically fixed in a metal box with an open front wall. A propane burner with a flame length of 175mm contacts the cable at a 45-degree angle from a position 450mm away from the upper fixed end of the specimen. If the burning damaged part of the sample is no more than 50mm from the lower part of the fixed end, the test passes.

◎ IEC60332-3/BS4066-3 flame retardant level (Flame Test On BunchedWires/Cables)

This is the flame retardant standard for bundled cables . The test stipulates that bundled 3.5m-long cable samples are fixed on a ladder test frame with iron wires. The number of samples is determined according to the non-metallic materials required by different classifications. The sample is hung vertically on the back wall of the combustion furnace, and air is introduced into the combustion furnace through the air inlet on the bottom plate. The propane flat burner contacts the sample with a flame of 750°C. The sample must not ignite within 20 minutes of vertical combustion under forced air blowing (air discharge 5m3/minute, wind speed 0.9m/second), and the cable will not ignite during the flame spread. Will self-extinguish within 2.5 meters. IEC60332 is divided into Class A, Class B, Class C and Class D to evaluate the flame retardant performance.

UL flame retardant standards

If any cable listed by UL meets a certain fire rating after testing and verification, the UL identification, fire rating and approval number can be printed on the cable.

◎ Pressurized level-CMP level (Plenum Flame Test/Steiner Tunnel Test)

This is the cable with the highest requirements in UL fire protection standards (Plenum Cable), the applicable safety standard is UL910. The experiment stipulates that multiple samples are laid on the horizontal air duct of the device and burned with an 87.9KW gas Bunsen burner (300,000BTU/Hr) for 20 minutes. The qualifying standard is that the flame must not extend more than 5 feet from the front of the gas Bunsen burner flame. The peak optical density is up to 0.5, and the average density value is up to 0.15.

This type of CMP cable is usually installed in air return plenum systems used in ventilation ducts or air handling equipment and is approved for use in Canada and the United States.

FEP/PLENUM materials that meet the UL910 standard have better flame retardant properties than low-smoke halogen-free materials that meet the IEC60332-1 and IEC60332-3 standards, and the concentration of smoke when burned is lower.

◎ Trunk level-CMR level (Riser Flame Test)

This is a commercial grade cable (Riser Cable) in the UL standard, and the applicable safety standard is UL1666. The experiment stipulates that multiple specimens are laid on a simulated vertical shaft and a specified 154.5KW gas Bunsen burner (527,500BTU/Hr) is used for 30 minutes. The qualifying standard is that flames cannot spread to the upper portion of a room that is 12 feet high. Trunk-level cables do not have smoke concentration specifications and are generally used for vertical and horizontal wiring on floors.

◎ Commercial grade - CM grade (Vertial Tray Flame Test)

This is a commercial grade cable (General Purpose Cable) in the UL standard, and the applicable safety standard is UL1581. The experiment stipulates that multiple specimens are laid on a vertical 8-foot-high support and burned (70,000 BTU/Hr) with a specified 20KW strip blowtorch for 20 minutes. The qualification criterion is that the flame cannot spread to the upper end of the cable and extinguish itself. UL1581 is similar to IEC60332-3C, except for the number of cables laid. Commercial-grade cables do not have smoke concentration specifications and are generally only used for horizontal wiring on the same floor and should not be used for vertical wiring on the floor.

◎ General grade - CMG grade (Vertial Tray Flame Test)

This is the general purpose cable (General Purpose Cable) in the UL standard, and the applicable safety standard is UL1581. The test conditions for commercial grade and general grade are similar, and both are approved for use in Canada and the United States. General-purpose cables do not have smoke concentration specifications and are generally only used for horizontal wiring on the same floor and should not be used for vertical wiring on the floor.

◎ Household grade - CMX level (Vertial Wire Flame Test)

This is a UL standard household grade cable (Restricted Cable), the applicable safety standard is UL1581, VW- 1. The experiment stipulates that the sample should be kept vertical, burned with a test blowtorch (30,000 TU/Hr) for 15 seconds, and then stopped for 15 seconds, repeated 5 times. The qualification standards are that the residual flame cannot exceed 60 seconds, the sample cannot be burned more than 25%, and the surgical cotton padded at the bottom cannot be ignited by falling objects. UL1581-VW-1 is similar to IEC60332-1, except that the burning time is different. This grade also has no smoke or toxicity specifications and is intended only for use in home or small office systems running a single cable. Such cables should not be laid in bundles and must be sleeved.

Smoke density, halogen content and toxicity level

◎ IEC60754-1/BS6425-1 Determination of halogen gas content (Emission Of Halogens)

This is IEC and specifications for hydrogen chloride (HCL) release concentrations in BS standards. Halogens contain fluorine, chlorine, bromine, iodine and the radioactive volatile element astatine, and their ingredients 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 air discharge rate is used to dissolve HCL into the water, 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 called a halogen-free cable (LSOH). Known as 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 determine whether they are "halogen-free". To determine whether it is completely halogen-free, the IEC60754-2 method can be used to determine whether it is completely halogen-free.

◎ IEC60754-2 Gas Acidity Measurement (Corrosivity)

This is the specification for the corrosivity of combustion gases in the IEC standard. This test is to measure the halogen acid produced by the material when it is burned. Gas acidity. It is measured by the pH value and conductivity of an 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 timing is started at the same time. During the first 5 minutes of the sample burning, the pH value and electrical conductivity properties were measured every 1 minute, and then every 5 minutes for the next 25 minutes. Generally, the PH value of halogen-free cable materials will be 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 in the material. It is worth noting that when the HCL content is greater than 2 mg/g and less than 5 mg/g (that is, when it meets the requirements of IEC60754-1), the pH value of the aqueous solution is also less than 4.3, that is, it does not meet the requirements of IEC60754-2.

◎ IEC 61034-1/ASTM E662 Smoke Density (Emission of Smoke)

This is the specification for smoke density in IEC and ASTM standards. The experiment consists of a 3m3 cube and a photometric measurement system with a light source. The rectangular box contains alcohol as a 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 vortex on the trough. When the alcohol burns, a recorder connected to the optical power supply records the amount of light reduction. Smoke density is measured by light transmittance. If it can reach 60% light transmission value (Light Transmittance), the cable material meets the low smoke standard. The higher the light transmittance, the less smoke the material releases when burning.

◎ ISO4589-2/BS2863 Oxygen Index LOI

This is the specification for oxygen index in 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 is. If the oxygen index of a material is 21%, it means that the material will burn automatically at normal room temperature. At normal room temperature, the oxygen content of air is 21%. Generally, the oxygen index of flame-retardant cables is greater than 33%.

◎ ISO4589-3/BS2782.1 Temperature Index TI (Temperature Index TI)

This is the specification for temperature index in ISO and BS standards. The oxygen index of the material will change with the temperature. It rises and falls. When the temperature rises and the oxygen index of the material drops to 21%, the material will automatically burn. This temperature 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%, and 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℃.

◎ NES713 Toxicity Index (Toxicity Index)

This is the British Naval Engineering NES standard for the toxicity of gases produced when cable materials are burned. Toxicity refers to the damage to the structure of living organisms. Or a property of functional disorder, the toxicity index refers to the total toxicity of all gases produced when the material is burned. The experiment stipulates that the combustion furnace is preheated to 800°C, the toxic substances contained in the cable materials will be burned separately, and then the air flow emission 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 more toxic 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. They should be called It is a low-toxic cable. Since CM, CMR and CMP cables need to pass strict UL fire protection standards, the cable materials used mostly contain halogen. CM and CMR cables are generally made of polyvinyl chloride (PVC) as the base material, and PVC materials contain chlorine; CMP cables are generally made of special Fluoron polytetrafluoroethylene (FEP) is the base material, and the FEP material contains fluorine.

The gas toxicity produced by such halogen-containing cables is several times greater than that of halogen-free cables, which poses a great hidden danger in fire safety. It may cause most casualties at the fire scene to be suffocated by poisonous gas instead of being burned to death. .

◎ IEC Fire Resistance Rating

Fire-resistant cables refer to the ability to maintain normal operation for a certain period of time when flames are burning, that is, maintaining the integrity of the circuit (Circuit Integrity). In order to evaluate the fire resistance of cables, the International Electrotechnical Commission and the British Electrotechnical Commission have formulated two standards, IEC331 and BS6387 respectively. In contrast, BS6387 has much higher fire resistance requirements than IEC331.

◎ IEC60331 flame retardant grade

In IEC60331-1999, the fire temperature requirement is 750℃/3h level, which means that it will burn for 3 hours when a voltage of 300 volts is applied at 750℃. wear.

◎ BS6387 flame retardant grade

BS6387 requires passing horizontal burning test, water spray test and mechanical impact vibration burning test. The horizontal combustion experiments are A-level 650°C/3h, B-level 750°C/3h, C-level 950°C/3h and S-level 950°C/3min. Class A means that the voltage level of 300 volts is applied at 650℃ and it burns for 3 hours without breakdown; Class B means that the voltage level of 300 volts is applied at 750℃ and it burns for 3 hours without breakdown; Class C means that the voltage level of 300 volts is applied at 950℃ without breakdown. It can burn for 3 hours without breakdown; S level means it can burn for 3 minutes without breakdown when a voltage of 300 volts is applied at 950℃. The water spray combustion experiment is divided into W level, which means that it will not break down when burning with 300 volts for 15 minutes and then sprayed with water for 15 minutes. The impact vibration combustion test is divided into X level 650℃/15min, Y level 750℃/15min and Z level 950℃/15min. X level means applying 300 volts at 650℃ while burning while mechanical shock and vibration every 30 seconds for 15 minutes. Breakdown; Class Y means no breakdown when a voltage of 300 volts is applied at 750℃ while burning and mechanical shock and vibration every 30 seconds for 15 minutes; Class Z means no breakdown when a voltage of 300 volts is applied at 950℃ while burning and mechanical shock and vibration every 30 seconds No breakdown for 15 minutes at a time. The highest level model required by BS6387 is CWZ.

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