The so-called fire-resistant waterproof cable is a cabl […]
The so-called fire-resistant waterproof cable is a cable that can maintain normal operation for a certain period of time under specified flame conditions, or a cable that can maintain a complete circuit under burning conditions. The selection of conductor materials, mica tape, insulating materials and auxiliary materials for fire-resistant cables is explained as follows.
1. Selection of Conductor Material and Conductive Core Structure
a. The melting point of aluminum conductor is 685℃ and the fire-resistant cable test should reach 750+50℃ in accordance with GB/T 19216. Obviously, aluminum conductors cannot be used as fire-resistant cables; the melting point of copper is above 1000℃, so it can be used. Conductor of fire-resistant cable.
b. Copper wire with a cross-section of 1.0mm2 and below does not melt at high temperatures, but because the core is too thin, it is easy to break due to local overheating and slight external influences, and lose the normal energizing function, so 1.0mm2 is not recommended Copper wires below and below are used as fire-resistant cables. Soft-structured bundles, due to the unevenness of the conductor surface, will cause great damage to the mica tape, and the performance of the produced fire-resistant cables will be unstable.
c. Large cross-section cable sector core conductors are not easy to make fire-resistant cables, and round core conductors are suitable for fire-resistant cables. Because the surface of the circular structure is smoother than that of the fan-shaped structure, the force of the mica tape is more uniform and will not cause damage to the mica tape, and the circular structure saves the mica tape and has a lower cost than the fan-shaped structure.
2. The choice of mica tape is based on the actual production situation of our company
Phlogopite and synthetic mica are often used. The refractory temperature of synthetic mica is higher than that of phlogopite. Since the national standard cancels the classification requirements for fire-resistant cables, in actual production, fire-resistant mica tapes can be selected according to customer requirements. Considering the safety of fire-resistant cables and ensuring the quality and stability of fire-resistant cables, it is recommended to use synthetic mica.
3. Selection of insulation materials The commonly used insulation materials for fire-resistant cables are mostly PVC, PE, XLPE, etc., but the effect of using PE and XLPE is better than that of PVC, because the insulation material of the cable has already burned at a high temperature of 750+50℃ It does not exist, but the residual materials after the burning of different insulating materials have different effects on the mica tape. The following is the explanation:
a. The main components of PVC are PVC resin and CaCO3 adhere to the outside of the mica tape according to its combustion mechanism. The mixture of its combustion solid residue CaO and Cacl2 is in a relatively stable state, adheres to the outside of the mica tape, and is burning. The process will generate internal stress, squeeze the mica tape, damage the mica tape, and affect the fire resistance.
b. PE and XLPE are pure hydrocarbon compounds with almost no fillers. The combustion products of co2 and water vapor escape naturally, and only a small amount of solid impurities remain on the mica tape, which will not cause damage to the mica tape.
Therefore, it can be seen that although PVC, PE and XLPE can be used for fire-resistant insulation, the effect of using PE and XLPE is better than that of PVC. 4. The selection of auxiliary materials As the auxiliary materials of fire-resistant cables, tape and filling are not key materials, but they should be based on the principle of the least residue generated after combustion.