In recent years, in the global power system fire accidents, the proportion of power supply interruptions due to power cable fires has been on the rise.
However, some electrical designers cannot distinguish the concepts of flame-retardant cables and fire-resistant cables, and do not know much about the structure and characteristics of the two, resulting in the inability to correctly design and select these two cables according to the power supply requirements, and conduct design agency or supervision on site. The laying workers of these two kinds of cables cannot be properly guided during work. Therefore, a comprehensive and correct understanding of flame-retardant and fire-resistant cables is the primary condition for the correct selection of them.
1. Flame retardant cable
Flame retardant cable refers to the cable in which the sample is burned under the specified test conditions, after the test fire source is removed, the spread of the flame is only within a limited range, and the residual flame or residual burn can be extinguished within a limited time. Flame retardant cables are self-extinguishing while maintaining the electrical properties and physical and chemical properties of ordinary cables, that is, they are not easy to burn, or when the cable catches fire by itself or an external fire source ignites, the cable will not continue after the fire is extinguished. Burning, or the burning time is very short (within 60 minutes), or the flame retardation length is very short.
Features: In the event of fire, it may be burnt out and cannot operate, but it can prevent the spread of fire. In layman's terms, in the event of a fire in the cable, the combustion can be limited to a local area without spreading, and other equipment can be protected to avoid greater losses.
Structural features: The structure of the flame-retardant cable is basically the same as that of the ordinary cable. The difference is that its insulating layer, sheath, outer sheath and auxiliary materials (taping and filling) are all or partially made of flame-retardant materials.
2. Fire resistant cable
Fire-resistant cables refer to the ability to maintain operation for a certain period of time under the condition of flame burning, that is, to maintain the integrity of the circuit. This type of cable has the ability to supply power for a certain period of time in the flame. It can continue to work (transmit current and signal) in the event of a fire, and its own fire delay is not included in the assessment. The flame-retardant cable stops working quickly when a fire occurs, and its function is to be flame-retardant and self-extinguishing without being affected. The fire-resistant cable maintains normal operation for 90 minutes in the flame combustion of 750 ~ 800 ℃.
Therefore, the main difference between fire-resistant power cables and flame-retardant cables is that fire-resistant cables can maintain normal power supply for a period of time when a fire occurs, while flame-retardant cables do not have this feature. This characteristic determines that fire-resistant cables play an important role in modern urban and industrial buildings, because once a fire occurs, the power supply circuits of control, monitoring, guidance and alarm systems must maintain normal operation. Therefore, it is also very necessary to choose a suitable and safe cable.