Application of flame-retardant and fire-proof cables in weak current engineering construction
Flame retardant cable（FlameRetardant）
The characteristic of flame retardant cable is to delay the spread of flame along the cable so that the fire will not expand. Due to its low cost, it is a widely used cable variety in fire-resistant cables. Whether it is a single cable or laid in bundles, when the cable is burned, the spread of the flame can be controlled within a certain range. Therefore, major disasters caused by cable fire and extended combustion can be avoided, thereby improving the fire protection level of cable lines. .
Halogen-free low smoke flame retardant cable (LSOH)
The characteristic of halogen-free and low-smoke cables is that they not only have excellent flame retardant properties, but the materials constituting the low-smoke and halogen-free cables do not contain halogens, are less corrosive and toxic when burned, and produce a very small amount of smoke, thereby reducing the impact on the human body. , instruments and equipment damage, which is conducive to timely rescue in the event of 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 Low Smoke Flame Retardant Cable (LSF)
The hydrogen chloride release amount and smoke concentration index of low-halogen low-smoke flame-retardant cables are between those of flame-retardant cables and halogen-free low-smoke flame-retardant cables. Low Halogen (Low Halogen) cable materials also contain halogen, but the content is lower.
This cable is characterized by not only flame retardant properties, but also releases less smoke and less hydrogen chloride when burned. This kind of low-halogen, low-smoke flame-retardant cable is generally made of polyvinyl chloride (PVC) as the base material, and is processed with high-efficiency flame retardants, HCL absorbers and smoke suppressants. Therefore, this flame retardant material significantly improves the combustion performance of ordinary flame retardant polyvinyl chloride materials.
Fire-resistant cable (FireResistant)
Fire-resistant cables can maintain normal operation for a certain period of time under flame burning conditions and maintain the integrity of the circuit (Circuit Intergrity). Fire-resistant and flame-retardant cables produce less acid gas smoke when burning, and their fire-resistant and flame-retardant properties are greatly improved. Especially when burning, accompanied by water spray and mechanical shock and vibration, the cable can still maintain complete operation of the line.
Flame retardant cable standards and grades
The main technical indicators of cable fire safety 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.
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 (Single Wire or Cable Vertical Burning Test FlameTestOnSingleVerticalInsulatedWires/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. A propane burner with a flame length of 175mm contacts the cable at an angle of 45 degrees from a position 450mm away from the upper fixed end of the sample. 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 (vertical burning test of bundled wires or cables FlameTestOnBunchedWires/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-shaped 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 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). 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 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.
Booster stage-CMP stage (supply air combustion test/Steiner Tunnel test PlenumFlameTest/SteinerTunnelTest)
This is the most demanding cable (PlenumCable) in the UL fire protection standard. 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 minute. The qualifying standard is that the flame must not extend more than 5 feet from the front of the gas Bunsen burner flame. The maximum peak value of optical density is 0.5, and the maximum average density value is 0.15.
This 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 compliant with UL910 standard, the oxygen index of general flame-retardant cables is greater than 33%.
ISO4589-3/BS2782.1 temperature index (TemperatureIndexTI)
This is the specification for temperature index in 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. 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 (ToxicityIndex)
This is the toxicity specification of gases produced when cable materials are burned in the British Naval Engineering NES standard. Toxicity refers to a property that causes damage or functional disorder to the structure of living organisms. The toxicity index refers to the toxicity of all gases produced when materials are burned. sum performance.
The experiment stipulates that the combustion furnace is preheated to 800°C, the toxic substances contained in the cable material 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 not to be burned to death but to be suffocated by poisonous gas. .
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 performance 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 can burn at a level of 300 volts at 750℃ for 3 hours without breakdown.
BS6387 flame retardant grade
BS6387 requires passing horizontal combustion test, water spray test and mechanical impact vibration combustion 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 burn without breakdown after applying 300 volts for 15 minutes and then spraying 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.
