1. If the conditions are good, the test shall be carried out in strict accordance with the relevant international and domestic standards. It is not allowed to find a fire source at will and ablate at will without measuring the flame temperature. If the corresponding test conditions are not available, the test conditions specified in the standard shall be simulated as much as possible;

　　2. If the test fails, double sampling shall be conducted again according to relevant standards, and the following conditions shall be checked, especially for wires with small size:

　　(1) Are there pinhole like micropores on the wire section and bubbles on the wire surface?

　　(2) Is there any small impurity particles or ordinary silicone rubber on the surface or section of the wire?

　　Silicone rubber is not compatible with other rubbers. If ordinary silicone rubber particles or other impurities are mixed in the extruder, the particles and impurities will be burned into powder after high temperature combustion, resulting in breakdown;

　　(3) If the sintering is not hard enough, check whether the environment is clean, whether there are other auxiliary powder and dust, whether the equipment is thoroughly clean, whether the operating personnel's work clothes, appliances and equipment are clean, and whether there are no dust and impurity particles;

　　3. In the case that the artificial strand is burned directly before extruding the sheath, the following situations should be avoided?

　　After 16 hours of storage after extrusion, the fire resistance test shall be conducted to release the stress generated during extrusion, otherwise it is easy to cause breakdown during burning;

　　When artificial stranded wire is used, it must be carried out according to the technical requirements of standards, process and operation procedures. The wire extruded from the ceramic silicone rubber must not be excessively twisted to produce excessive stress, otherwise it is easy to break down in the process of burning;

　　After stranding, do not wind hard wire such as hard conductor, iron wire, aluminum wire or other hard wires on the outside of the stranding, because after winding, there will be point and linear stress points on the surface of the ceramic silicone rubber cable, the surface stress is uneven, the stress is relatively concentrated, and it is easy to produce breakdown in the process of burning;

　　4. In the process of the test: ablate according to the standard, use the yellow outer flame for ablation, adjust the flow rate and mixing ratio of propane and air according to the standard, avoid incomplete combustion, and produce a large amount of carbon deposit on the surface of the test cable; at the same time, do not open the air flow too much, and produce air flow like oxygen welding, which has impact and cutting effect on the cable, So the experiment failed

　　5. In the design of medium voltage fire-resistant cable, attention should be paid to the temperature protection design of the insulation layer. The cable material with oxygen index of about 42 should be used for the oxygen isolation layer, the cable material with oxygen index of about 38 should be used for the outer sheath, the alkali free glass cloth should be used for the inner glass cloth, and the ceramic silicone rubber or alkali free glass wire should be used for the filling layer, so as to ensure that the insulation layer does not melt and deform during the test It is better to use cross-linked polyethylene than irradiation cross-linked polyethylene. The temperature resistance of irradiation cross-linked polyethylene is high, up to 180-200 ℃.