The main characteristic of flame-retardant cables is that they are resistant to ignition or, if they do, combustion is confined to a certain area, thus preventing major disasters caused by the spread of fire. Fire-resistant cables are cables that can maintain normal operation even after prolonged exposure to and after a fire. IEC standards require that fire-resistant cables can withstand a flame of 750-800°C for 3 hours at rated voltage without insulation breakdown. This ensures their continued use in high-rise buildings, petrochemical plants, mines, aircraft, ships, elevators, and emergency power supplies, where fire safety requirements are more stringent.
1. The fire-resistant cable mentioned above, which can withstand a flame of 750-800°C for 3 hours without insulation breakdown, shouldn't it be true? It should be able to maintain current flow, not breakdown? At 800°C, the insulation would likely have melted.
2. It shouldn't be able to break down, otherwise it would have short-circuited, so how could power still be supplied?
3. Fire-resistant cables generally provide reliable service in times of crisis, and only for a short period of time. For example, general fire safety requirements dictate that cables can continue operating for two hours under fire conditions. Mineral-insulated cables, on the other hand, are designed to operate continuously in high-temperature environments, such as steelmaking furnaces, where they heat up quickly.
4. The Role of the Mica Wrap and the Insulation Layer. Under normal cable operation, the insulation layer is responsible for the primary electrical performance. If a cable catches fire or is exposed to a fire, the insulation layer will quickly burn away. The mica layer provides insulation and ensures the cable can be lit for a period of two hours. The fire-resistant operating temperature of fire-resistant cables is determined by the characteristics of the fire. Generally, an open flame temperature of 600-700°C is considered high under non-sustained conditions. This explains why aluminum conductors are not used for fire-resistant cables. If higher temperatures and long-term operation at high temperatures are required, mineral-insulated cables should be used.
