New Edition of National Standard for Wire and Cable

New Edition of National Standard for Wire and Cable

2019-07-19 10:32
As for the permissible long-term working temperature of wire and cable cores,rubber insulation is usually 65 C,PVC insulation is 70℃,cross-linked polyethylene insulation is 90℃,and conductor's maximum permissible temperature in short circuit(the longest duration is not more than 5 s):PVC insulation is 160 C,cross-linked polyethylene insulation is 250℃.
1.The difference between XLPE cable and PVC cable:
1.Low-voltage cross-linked(XLPE)cables have developed rapidly since they were put into use in the mid-1990s.At present,XLPE cables and polyvinyl chloride(PVC)cables account for half of the market share.Compared with PVC cables,XLPE cables have higher carrying capacity,stronger overloading capacity and longer service life(the thermal life of PVC cables is usually 20 years when the environment is good,while XLPE cables is 40 years);when PVC is burned,a large amount of black smoke and toxic gases will be released,while when XLPE is burned,halogen toxic gases will not be produced.The advantages of cross-linked cables are increasingly recognized by design and use departments.
2.The burning time of ordinary PVC cables(insulation and sheath)is delayed and ignited rapidly,which contributes to the fire.The power supply capacity is lost within 1 to 2 minutes.The black smoke released by the burning decomposition can reach the level of invisibility,which makes it difficult for people to breathe and evacuate.More seriously,the decomposition and release of highly toxic and corrosive halogen gases such as hydrogen chloride(HCL)and dioxins during combustion of PVC is the main cause of death in fire(accounting for 80%of the fire death factors),and the dilute conductive film of hydrochloric acid is attached to electrical equipment,which seriously reduces the insulation performance of equipment and causes secondary disasters that are difficult to remove.Harm.
II.Flame Retardant Wires and Cables
1.Flame-retardant wires and cables should have flame-retardant characteristics.According to GB/T 18380.3-2001,flame-retardant wires and cables can be divided into three grades:A,B and C.The flame-retardant performance of A grade is the highest.
The American Institute of Standards and Technology has conducted comparative combustion tests on 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 of escape time than Non-Flame-Retardant wires.
B.The material burned by flame-retardant wire is only 1/2 of that of Non-Flame-Retardant wire.
C.The heat release rate of flame-retardant wire is only 1/4 of that of Non-Flame-Retardant wire.
D combustion produces only 1/3 of the toxic gas of non-flame retardant products.
E.Smoke production performance,flame retardant products and non-flame retardant products have no obvious difference.
2.Halogen-free low smoke wire and cable
Halogen-free low-smoke wire and cable should have halogen-free,low-smoke and flame retardant properties.
GB/T 17650.2-1999(halogen-free test)GB/T 17651.2-1998(low smoke test)
PH Weighted Conductivity Minimum Transmittance
PH>4.3 r<10us/mm T>60%
3.Refractory cables
A.Fire test index of refractory cable(fire supply temperature and time).GB12666.6-90 of Test Method for Fire Resistance Characteristics of Wire and Cable stipulates:Class A 950-1000 degrees C,90 minutes;Class B 750-800 degrees C,90 minutes.The IEC 331-1970 standard stipulates 750 degrees C and 3 hours,which is equivalent to Class B standard in China.From the latest draft IEC 60331,which was voted on by IEC,the temperature of fire supply is still 750~800 C for 3 hours.If this standard is passed,China will adopt it equally,then refractory cables will not be classified as A and B.
B.Fire-resistant wires and cables can be divided into flame-retardant and Non-Flame-Retardant wires and cables according to their different non-metallic materials.Domestic products of refractory wires and cables are mainly mica-coated conductors and extruded flame retardant cladding.Most of them are grade B products.At present,refractory cables with special synthetic mica tape and mineral insulation(copper core copper sleeve,magnesium oxide insulation,also known as MI)can meet the grade A standard.Mineral insulated refractory cables have the characteristics of non-flammability,smoke-free,corrosion-resistant,non-toxic,impact-resistant and spray-resistant.They are called fire-proof cables.The fire-proof performance is the most prominent among the varieties of fire-resistant cables and cables.However,the manufacturing process is complex,the price is high,the manufacturing length is limited,the bending radius is large,the insulation is easily damp,and the section is 25mm2.At present,the above specifications can only provide single core products.Permanent dedicated terminals and intermediate connectors must be used.The installation and construction are more complex.
III.New Products of Construction Wire and Cable
According to GB5023.3-1997,the rated voltage(insulation grade)of 0.5-1.0 mm2 conductor is 300/500V,and that of 1.5-240 mm2 conductor is 450/750 V.At present,the application of general polyvinyl chloride wiring(BV)is still dominant in China,but new wiring varieties suitable for construction projects have been developed successively.
1.Cross-linked polyolefin insulated wiring(Model BYJ)
As mentioned above,the advantages of cross-linking materials have been widely recognized.Many countries have applied cross-linking technology to the field of electrical wires,replacing polyvinyl chloride(PVC)wires as construction electrical wires,and showing great advantages.Some manufacturers in and outside the province can produce series of cross-linked wires,and the production cost has been basically equal to that of BV wires.Cross-linked wire is a relatively ideal new type of construction wiring.European and American countries are vigorously promoting the application of cross-linked wire.In the Tenth Five-Year Plan for the development of national wire and cable industry,expanding the application of cross-linked wire will be included in the main development goals of construction wiring.Engineering application in the province is at the initial stage.
2.Environmentally friendly cables(eco-material cables with flame retardancy,also known as EM cables)
From a technical point of view,environmental-friendly cable is a higher-stage product of wire and cable,which is in line with the trend of the times and development trend.It has received extensive attention since it came out.A series of production and application standards have been formulated in developed countries such as Europe,the United States and Japan,and vigorously promoted and applied.Environmentally friendly cable.


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