Refers to the performance that the sample is burned in the flame under the specified test conditions and can still maintain normal operation within a certain period of time. Its basic characteristic is: the cable can still maintain the normal operation of the line for a period of time under burning conditions. In layman's terms, in case of fire, the cable will not burn at once, and the circuit is safer. Therefore, the main difference between fire-resistant cables and flame-retardant cables is that fire-resistant cables can maintain normal power supply for a period of time when a fire occurs, and flame-retardant cables do not have this feature. The cable is mainly used in emergency power supply to the user's fire equipment, fire alarm equipment, ventilation and exhaust equipment, guide lights, emergency power sockets, emergency elevators and other power supply circuits. Common fire-resistant cables are classified into Class A and Class B: Class B cables can withstand burning for at least 90 minutes in a flame of 750°C to 800°C and a rated voltage without the cable being broken (ie, the 3A fuse does not blow). Based on the improvement of the manufacturing process of the refractory layer and the addition of the refractory layer, a class A refractory cable was developed, which can withstand burning for at least 90 minutes in the flame of 950 ℃ ~ 1 000 ℃ and the rated voltage without the cable being punctured (That is, the 3A fuse does not blow). Class A fire-resistant cables have better fire resistance than Class B.
(1) When fire-resistant cables are used in dense cable tunnels, cable interlayers, or located 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 cable configurations is small, Class B fire-resistant cables may be used.
(2) Fire-resistant cables are mostly used as power supply circuits for emergency power supplies, which require normal work in the event of a fire. Because the ambient temperature rises sharply during a fire, in order to ensure the transmission capacity of the line and reduce the voltage drop, the loop of the power supply line that is long and the voltage drop is strictly limited should be enlarged by at least one step.
(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 should be reduced as much as possible in the installation to ensure that the lines can work normally in fires. If branch wiring is required, the joints should be fireproofed.