Fire protection cables are a special type of cable made of oxygen resistant, flame-retardant, and fire-resistant materials. They have the properties of non melting, non dissolving, non flame retardant, low smoke, low halogen, and low toxicity. In the event of a fire, fire cables can maintain normal operation and provide stable electrical support for fire equipment.

Specifically, the characteristics of fire cables include:
1. Good flame retardancy: Under the action of flames, fire cables can self extinguish and will not spread outwards, thus greatly protecting the safety of people and property.
2. High temperature resistance: Fire protection cables can maintain normal operation in high temperature environments (such as working at 1000 ℃ for more than 4 hours), ensuring the normal operation of fire protection facilities.
3. Impact and tension resistance: This type of cable has excellent mechanical properties and can withstand certain physical impacts and tensions.
4. Good extensibility: Fire cables have good extensibility and can adapt to various complex application environments.

In addition, fire cables are widely used in fire equipment power supply systems, such as fire pumps, fire elevators, fire monitoring, etc. Fire cables also play an important role in emergency lighting power supply systems and important locations.
The design and application of fire cables are aimed at ensuring that critical equipment and systems can continue to operate in emergency situations such as fires, providing necessary support for rescue and evacuation. Therefore, fire cables play an irreplaceable role in fire protection systems.
The fire resistance limit time requirement for fire cables generally ranges from 0.5 to 3 hours, which mainly depends on their actual application site and safety requirements level.
In high demand environments such as high-rise buildings, subways, and tunnels, the fire resistance time of fire cables is required to be as long as 2-3 hours to ensure the stable operation of facilities in the event of a fire. In general residential buildings and other residential buildings, the fire resistance time requirements for fire cables are relatively low.
In addition, according to national standards, there are specific requirements for the fire resistance rating of fire power lines. For example, the A-level fire resistance rating requires cables to be continuously stored at a high temperature of 800 ℃ for 180 minutes without catching fire or melting. The B, C, and D grades have corresponding refractory time requirements at high temperatures of 650 ℃, 550 ℃, and 450 ℃, respectively.
Therefore, when selecting and using fire cables, it is necessary to determine their fire resistance limit time based on specific application scenarios and safety requirements, and ensure compliance with relevant national standards and regulatory requirements. At the same time, regular inspection and maintenance are also crucial to ensure that fire cables can function properly at critical moments.