Comprehensive knowledge of flame-retardant cables and fire-resistant cables

Date：2020/10/28　　Clicks：1193

The cable industry is used to refer to cables with certain fire resistance properties such as FireRetardant, LowSmokeHalogenFree (LSOH) or LowSmokeFume (LSF), FireResistant, etc., which have certain fire resistance properties. 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. 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 of cables, the flame spread 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 impact on humans. , The damage of instruments and equipment is conducive to timely rescue in case of fire. Although the halogen-free low-smoke flame-retardant cable has excellent flame retardancy, corrosion resistance and low smoke concentration, its mechanical and electrical properties are slightly worse than ordinary cables.

Low smoke flame retardant cable (LSF)

Low-halogen, low-smoke and 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 (LowHalogen) 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 performance, 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 cable (FireResistant)

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 (CircuitIntergrity). 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.

Flame retardant cable standards and grades

The main technical indicators related to fire safety of cables are the flame retardancy of CO2 cables, the density of smoke and the toxicity of gases. The US fire protection standards pay more attention to the first two issues, but Europe and the US have completely different views on fire safety.

The American traditional concept believes that the root of fire is the production of carbon monoxide (CO) gas and the heat release of CO into CO2 during the subsequent combustion process. Therefore, controlling the heat release during the combustion process can reduce the hazard of fire. European tradition has 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 rating

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 in an inclined and vertical position (corresponding to GB12666.3 and GB12666.4 standards in China). IEC60332-3 (corresponding to GB12666.5-90 in China) is used to evaluate the flame retardant ability of bundled cables when burning vertically. In contrast, the requirements for flame retardant ability of bundled cables when burning vertically are much higher.

IEC60332-1/BS4066-1 flame retardant grade (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, 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 (Bundled wires or cables vertical burning test FlameTestOnBunchedWires/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 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 assess the flame retardant performance.

UL flame retardant standard

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 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 should be laid on the horizontal duct of the device and burned with an 87.9KW gas Bunsen burner (300,000BTU/Hr). minute. The eligibility criterion is that the flame cannot extend beyond 5 feet from the front end of the gas Bunsen burner. The maximum peak optical density is 0.5, and the maximum average density value is 0.15.

This kind of CMP cable is usually installed in the air return booster 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

Trunk level-CMR level (RiserFlameTest)

This is a commercial-grade cable in the UL standard (RiserCable), 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 (VertialTrayFlameTest)

This is a commercial grade cable in the UL standard (General PurposeCable), and the applicable safety standard is UL1581. The experiment stipulates that multiple samples should be laid on a vertical 8-foot-high bracket and burned with a prescribed 20KW ribbon blowtorch (70,000BTU/Hr) 20 minute. 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, but the number of cables is different. Commercial-grade cables do not have smoke density specifications, and are generally only used for horizontal wiring on the same floor, not for vertical wiring on the floor.

General level-CMG level (VertialTrayFlameTest)

This is a General Purpose Cable in the UL standard. The applicable safety standard is UL1581. The test conditions for 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, not for vertical wiring on the floor.

Household level-CMX level (VertialWireFlameTest)

This is a household-grade cable in the UL standard (RestrictedCable). The applicable safety standard is UL1581, VW-1. The test stipulates that the sample should be kept vertical, burned with a test burner (30,000TU/Hr) for 15 seconds, and then stopped for 15 seconds Bell, repeat 5 times.

The qualification standard is that the residual flame should not exceed 60 seconds, the sample should not burn 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 type of cable should not be used in bundles and must be sleeved.

Smoke density, halogen content and toxicity grade

IEC60754-1/BS6425-1 Determination of halogen gas content (EmissionOfHalogens)

This is the specification for the release concentration of hydrogen chloride (HCL) in the IEC and BS standards. Halogen contains 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, and the HCL is dissolved into the water using the air flow 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 5mg/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 specification for the corrosiveness of combustion gas in the IEC standard. 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.

IEC61034-1/ASTME662 Smoke Density (Emission of Smoke)

This is the smoke density specification in the IEC and ASTM standards. The experiment consists of a 3m3 cube and a photometric system with a light source. The rectangular cao is equipped with alcohol as the combustion source. A blower with a power of 10-15m3/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 light attenuation.

Smoke density is measured by light transmittance. If it can reach 60% light transmission value (LightTransmittance), the cable material will meet the low smoke standard. The higher the light transmittance, the less smoke the material emits when burning.

ISO4589-2/BS2863 Oxygen Index (OxygenIndexLOI)

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. 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 (TemperatureIndexTI)

This is the temperature index specification 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, and the temperature will be 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 (ToxicityIndex)

This is the British naval engineering NES standard for the toxicity of the gas generated when the cable material is burned. Toxicity refers to a property that causes damage or dysfunction to the biological structure. The toxicity index refers to the toxicity of all gases produced when the material is burned. Sum performance.

The experiment stipulates that when the combustion furnace is preheated to 800℃, the toxic substances contained in the cable materials 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 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, 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 use special Fluorine polytetrafluoroethylene (FEP) is the base material, and the FEP material contains fluorine.

The toxicity of the gas 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, which may cause most of the casualties at the fire scene to be suffocated by poisonous gas instead of being burned. .

IEC fire resistance rating

Fire-resistant cable refers to the normal operation that can maintain a certain period of time when the flame is burning, that is, to maintain the integrity of the circuit (CircuitIntegrity). In order to evaluate the fire resistance performance of cables, the International Electrotechnical Commission and the British Electrotechnical Commission separately Two standards of IEC331 and BS6387 have been set. In contrast, BS6387 has a much higher fire resistance requirement than IEC331.

IEC60331 flame retardant rating

In IEC60331-1999, the fire temperature requirement is 750℃/3h, which means that it will burn for 3 hours at 750℃ without breakdown.

BS6387 flame retardant grade

BS6387 requires horizontal combustion test, water spray test and mechanical shock vibration combustion test. The horizontal combustion experiment is A grade 650℃/3h, B grade 750℃/3h, C grade 950℃/3h and S grade 950℃/3min.

Class A means that it will burn for 3 hours at 650℃ without breakdown; Grade B means it will burn for 3 hours at 750℃; Grade C means it will not break down at 950℃ No breakdown after burning for 3 hours; S grade means no breakdown after burning for 3 minutes at 950°C with a voltage level of 300 volts.

The water spray combustion test is divided into W class, which means that it will burn for 15 minutes after applying a voltage of 300 volts and then spray and burn for 15 minutes without breakdown. The shock vibration combustion experiment is divided into X-level 650℃/15min, Y-level 750℃/15min and Z-level 950℃/15min. X-level means that when 300 volts is applied at 650℃, it burns while burning every 30 seconds. Breakdown; Class Y means that when 300 volts is applied at 750°C while burning, mechanical shock vibration once every 30 seconds without breakdown; Class Z means that 300 volts are applied at 950°C while burning and mechanical shock every 30 seconds. No breakdown for 15 minutes at a time. The highest level model required by BS6387 is CWZ.