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National standard for wire and cable

2022-12-19 11:03:47 浙江安和线缆股份有限公司 Viewd 397

Regarding the allowable long-term operating temperature of wire and cable cores, rubber insulation is usually 65℃, polyvinyl chloride insulation is 70℃, and crosslinked polyethylene insulation is 90℃; the maximum allowable temperature of the conductor during a short circuit (the longest duration does not exceed 5s): polyvinyl chloride insulation is 160℃, and crosslinked polyethylene insulation is 250℃.


1. The difference between XLPE cable and PVC cable:


1. Low-voltage crosslinked (XLPE) cables have developed rapidly since they were put into use in the mid-1990s. They currently account for half of the market share with polyvinyl chloride (PVC) cables.Compared with polyvinyl chloride cables, crosslinked cables have higher carrying capacity, strong overload capacity, and long service life (the thermal life of PVC cables is generally 20 years when the environment is better, while the thermal life of XLPE cables is generally 40 years); when PVC is burned, it will decompose and release a lot of black smoke and toxic gases, while XLPE will not produce halogen toxic gases when burned. The advantages of crosslinked cables are increasingly recognized by design and use departments.


2. Ordinary PVC wires and cables (insulation and sheathed) burn rapidly when they are delayed, fueling the fire, and the power supply capacity is lost within 1 to 2 minutes. The black smoke released by their combustion and decomposition can reach the level of invisible fingers, causing breathing and evacuation difficulties for personnel.More seriously, when PVC burns, it will decompose and release highly toxic and corrosive halogen gases such as hydrogen chloride (HCL) and dioxin. It is the main cause of death in fires (accounting for 80% of fire deaths), and it forms a dilute hydrochloric acid conductive film attached to electrical equipment, seriously reducing the insulation properties of the equipment, forming a secondary disaster that is difficult to remove.




2. Flame-retardant wire and cable


1. Flame-retardant wires and cables should have flame-retardant properties. According to the "Combustion Test Method of Bundled Wires and Cables" GB/T18380.3-2001, they can be divided into three flame-retardant grades: A, B, and C, with the highest flame-retardant performance at Grade A.The American Institute of Standards and Technology conducted a comparative combustion test of flame-retardant and non-flame-retardant wires. The following test results can illustrate the importance of using flame-retardant wires and cables.:


A. Flame-retardant wires can provide more than 15 times the escape time than non-flame-retardant wires;


B. The material burned by flame-retardant wires is only 1/2 of that of non-flame-retardant wires.;


C. The heat release rate of flame-retardant wires is only 1/4 of that of non-flame-retardant wires.;


D. The amount of toxic gas produced by combustion is only 1/3 of that of non-flame retardant products.;


E. Smoke-producing properties, there is no obvious difference between flame-retardant products and non-flame-retardant products.



2. Halogen-free and low-smoke wire and cable


Halogen-free and low-smoke wires and cables should have halogen-free, low-smoke and flame-retardant properties. The indicators are: GB/T17650.2-1999 (halogen-free test) GB/T17651.2-1998 (low-smoke test) PH weighted conductivity minimum light transmittance PH≥4.3r≤10us/mm T≥60%



3. Fire-resistant cable


a.The combustion test indicators of fire-resistant cables (fire supply temperature and time), the "Test method for Fire-resistant Characteristics of Wires and Cables" GB12666.6-90 are specified as: Grade A 950~1000℃, 90 minutes; Grade B 750~800℃, 90 minutes.The IEC331-1970 standard stipulates that it is 750℃ and 3 hours, which is equivalent to our country's Class B standard.From the new draft of IEC60331 recently voted by IEC, the fire supply temperature is still 750℃~800℃ for 3 hours. If this standard is passed, my country will adopt it equally, and the fire-resistant cables will not be classified as A and B.


b.Fire-resistant wires and cables can be divided into flame-retardant and fire-resistant wires and cables and non-flame-retardant and fire-resistant wires and cables according to their different non-metallic materials.Fire-resistant wire and cable domestic products use mica-coated conductors and extruded flame-retardant sheathed layers as the main body. Most of them are grade B products. At present, special synthetic mica belts and mineral insulation (copper core, copper sleeve, magnesium oxide insulation, also known as MI) are used to meet the grade A standard. Fire-resistant cables.Mineral insulated fire-resistant cables have the characteristics of non-combustible, smokeless, corrosion-resistant, non-toxic, impact-resistant, and spray-resistant. They are called fire-resistant cables. Fire-resistant properties are the most prominent among fire-resistant wire and cable varieties, but the manufacturing process is more complex, the price is higher, the manufacturing length is limited, the bending radius is large, the insulation is susceptible to moisture, and the cross-section of 25mm2 and above specifications can only provide single-core products, and permanent special terminals and intermediate connectors must be used, and the installation and construction are more complicated.