Selection of Flame Retardant Wire and Cable

Update:31 Jul 2017

   In GB 12666. 5-90 "Bundle wire and cable combustion […]

   In GB 12666. 5-90 "Bundle wire and cable combustion test method", the number of cable samples, according to the length of each bundle of cable containing non-metallic materials in different volumes, divided into Class A, B , C class three types.
For the urban rail transit power supply system, the project cable to choose what kind of flame retardant grade, China has no corresponding standards. From the past practice of running, the choice of high flame retardant cable in the project, in reducing the cable fire probability, enhance system security, reduce the economic losses caused by failure and so on more advantages.
For the same type of Class A flame retardant cable and Class C flame retardant cable, the price difference of about 15% to 20%. Therefore, the type of flame retardant cable selected in the project, the need to combine the number of cables in the project, the intensity of cable laying, fire probability, enhance the safety requirements and engineering investment and other comprehensive consideration.
   For the oxygen index, here is a brief introduction. Oxygen index refers to the object in the nitrogen and oxygen mixed gas to maintain the minimum percentage of oxygen combustion. Therefore, the higher the oxygen index of the object, the better the flame retardant properties of the object. On the choice of the use of flame retardant cable insulation or insulation sheath materials such as oxygen index assessment requirements, the cable does not make oxygen index assessment.
The smoke density of cable burning and the selection of material properties of outer sheath
The smoke density at the time of cable burning is specified in the GB / T 17651 1998 standard, that is, when the obtained light transmittance exceeds 60%, it can be called low smoke. There is no relevant standard for the halogen-free, low-halogen performance of the jacketed material from the cable. General people believe that the cable burning gas when the content of halogen acid less than 5 mg / g, halogen-free; halogen acid equivalent content of 5 ~ 100mg / g, low halogen.
In the combustion test of the cable, the content of the haloguanate in the combustion gas is only less than 5 mg / g, so that the low smoke standard of 60% light transmittance can be achieved. Low-halogen products when the smoke concentration of light transmission rate is generally between 30% to 50%, less than the requirements of low smoke standards. Generally speaking, low smoke low halogen flame retardant cable is not accurate, should be low smoke zero halogen flame retardant cable or low halogen flame retardant cable.
35 kV XLPE insulated flame-retardant cable jacket, generally halogen-free polyolefin and other materials and low-halogen polyvinyl chloride and other materials. When the cable burns, the toxic acid of the ferric acid can cause harm to the human body and may even endanger the safety of human life. Therefore, it is also necessary to make the requirements for the smoke density of the outer jacket material and the content of the halogenated acid gas.
   The determination of the total amount of halogenated acid in the low-halogen product can be determined by the method specified in GB / T 17650. 1 -1998, that is, the determination of the content of the halo acid in the combustion gas. For halogen-free products, the content of the halogenated acid gas is difficult to measure with the above method. When the equivalent content of the acid is less than 5 mg / g, the test is carried out by the method specified in GB / T 17650. 2 -1998, that is, the pH and the conductivity are measured to determine the acidity of the gas.
   Therefore, for low-smoke halogen-free flame retardant cable, it is necessary to transmit the pH value, conductivity and light transmittance of the escape gas during the combustion of the jacket. For low-halogen flame-retardant cable, the combustion of the bath when the content of halogen acid gas requirements, if necessary, when the cable burning light transmission requirements. For most of the elevated urban rail transit power supply system, from the technical and economic point of view, the cable jacket material should use low-halogen materials.