Fire-resistant cable

Fire-resistant cable refers to the cable that can maintain safe operation for a certain time under the condition of flame burning. Fire-resistant cables are widely used in high-rise buildings, subways, underground streets, large power stations and important industrial and mining enterprises and other places related to fire safety and fire fighting and lifesaving, such as power supply lines and control lines for emergency facilities such as fire fighting equipment and emergency guide lights.

Classification of fire-resistant cables

In China, common fire-resistant cables are divided into Class A and Class B: Class B cables can withstand combustion for at least 90 min in a flame of 750 ℃~800 ℃ and rated voltage without breakdown of the cable (that is, the 3A fuse does not blow). On the basis of improving the manufacturing process of the refractory layer and adding the refractory layer, a Class A refractory cable has been developed. It can withstand combustion for at least 90 min under the flame and rated voltage of 950 ℃~1000 ℃ without breakdown of the cable (that is, the 3A fuse does not blow). The fire resistance of Class A fire-resistant cable is better than that of Class B. In addition, mineral-insulated cable is a kind of fire-resistant cable with better neutral energy. It is made of copper core, copper sheath and magnesium oxide insulating material, which is referred to as MI (mineral-insulated cables) cable. This cable is completely composed of inorganic substances, while the fire resistant layer of ordinary fire resistant cable is composed of inorganic substances and general organic substances. Therefore, the fire resistance of MI cable is better than that of ordinary fire resistant cable, and it will not decompose and produce corrosive gas due to combustion. MI cable has good fire resistance and can work under 250 ℃ for a long time. At the same time, it has the characteristics of explosion protection, strong corrosion resistance, large current carrying capacity, radiation resistance, high mechanical strength, small size, light weight, long service life and smoke-free. However, due to the high price, complex process and great construction difficulty, the cable with good fire resistance can be used in places with high fire resistance requirements and acceptable economy, such as oil irrigation areas, important wood structure public buildings and high temperature places.

Selection of fire-resistant cable

According to the specific characteristics of fire-resistant cables, designers should pay attention to the following issues when designing and selecting: (1) When fire-resistant cables are used in cable tunnels and cable interlayer with dense cables, or in flammable places such as oil pipes and oil depots, Class A fire-resistant cables should be selected first. In addition to the above conditions and when the number of cables is small, Class B fire-resistant cables can be used. (2) Fire-resistant cables are mostly used as power supply circuit of emergency power supply, which requires normal operation in case of fire. As the ambient temperature rises sharply in case of fire, in order to ensure the transmission capacity of the line and reduce the voltage drop, the section of the fire-resistant cable should be enlarged by at least one gear for the circuit with long power supply line and strictly limited allowable voltage drop. (3) Fire-resistant cables cannot be used as high-temperature resistant cables. (4) In order to reduce the failure probability of cable joints in fire accidents, the number of joints shall be minimized during installation to ensure that the line can work normally in fire. If branch wiring is required, the joint shall be fireproof.