Classification of Fire-Resistant Cables

In China, standard fire-resistant cables are categorized into Class A and Class B. Class B cables can withstand exposure to flames at 750°C–800°C while under rated voltage for at least 90 minutes without suffering electrical breakdown (i.e., without blowing a 3A fuse). Class A fire-resistant cables were subsequently developed through improvements in manufacturing processes and the enhancement of the fire-resistant layer; these cables can withstand flames at 950°C–1,000°C under rated voltage for at least 90 minutes without electrical breakdown (i.e., without blowing a 3A fuse). Class A cables offer superior fire resistance compared to Class B cables. Additionally, mineral-insulated (MI) cables represent a high-performance type of fire-resistant cable; they are constructed from copper cores, copper sheaths, and magnesium oxide insulation. Unlike standard fire-resistant cables-which utilize a composite fire-resistant layer of inorganic and organic materials-MI cables feature a fire-resistant layer composed entirely of inorganic materials. Consequently, MI cables offer superior fire resistance and do not decompose to release corrosive gases during combustion. MI cables possess excellent fire-resistant properties and can operate continuously at high temperatures of 250°C. They also offer advantages such as explosion-proof capabilities, strong corrosion resistance, high current-carrying capacity, radiation resistance, high mechanical strength, compact size, light weight, long service life, and smokeless operation. However, due to their high cost, complex manufacturing, and installation difficulties, they are typically employed in settings where fire resistance is critical and the cost is justifiable-such as oil storage areas, important public buildings with timber structures, and high-temperature environments.