Fire-resistant wires and cables are specialized cables that aren't always in stock at most factories, but can be custom-made. They're more expensive than conventional cables, so what are their characteristics? Let's explore the characteristics of fire-resistant cables.
What are fire-resistant cables?
1. Fire-resistant cables are cables that, under specified test conditions, can maintain normal operation for a specified period of time even when exposed to flames. Their fundamental characteristic is that they can maintain normal operation for a period of time even under fire. In layman's terms, in the event of a fire, the cable won't immediately burn, making the circuit safer.
Analysis reveals that the main difference between fire-resistant and flame-retardant cables is that fire-resistant cables can maintain normal power supply for a period of time in the event of a fire, while flame-retardant cables lack this characteristic.
This characteristic makes fire-resistant cables crucial in modern urban and industrial buildings, as power supply circuits for control, monitoring, guidance, and alarm systems must remain operational in the event of a fire. Therefore, we recommend that this cable be primarily used in power supply circuits connecting emergency power supplies to user fire-fighting equipment, fire alarms, ventilation and smoke exhaust systems, guide lights, emergency power outlets, and emergency elevators.
2. Structural Features of Fire-Resistant Cables:
The structure of fire-resistant cables is essentially the same as that of ordinary cables. The difference lies in the use of copper conductors (copper has a melting point of 1083°C), which have excellent fire-resistant properties, and an additional fire-resistant layer between the conductor and the insulation. This layer is wrapped with multiple layers of mica tape. Because the allowable operating temperatures of different mica tapes vary significantly, we recommend that the mica tape is crucial to the fire resistance of the cable.
3. Classification of Fire-Resistant Cables:
In China, ordinary fire-resistant cables are classified into Class A and Class B. Class B cables can withstand flames of 750°C to 800°C at rated voltage for at least 90 minutes without breaking down (i.e., a 3A fuse will not blow). The editor suggests that by improving the manufacturing process for the fire-resistant layer and adding additional fire-resistant layers, Class A fire-resistant cables have been developed. These cables can withstand flames of 950°C to 1000°C and rated voltage for at least 90 minutes without breaking down (i.e., a 3A fuse will not blow). Class A fire-resistant cables offer superior fire resistance to Class B cables.
Mineral insulated cables, also known as MI cables, are a superior type of fire-resistant cable. They are made of a copper core, copper sheath, and magnesium oxide insulation. The fire-resistant layer of these cables is composed entirely of inorganic materials, while the fire-resistant layer of conventional fire-resistant cables is a composite of inorganic and organic materials. Therefore, MI cables offer superior fire resistance and do not produce corrosive gases due to decomposition during combustion. MI cables offer excellent fire resistance and can operate at temperatures of 250°C for extended periods. They are also explosion-proof, corrosion-resistant, have a high current carrying capacity, are radiation-resistant, have high mechanical strength, are compact and lightweight, have a long lifespan, and are smokeless. However, it is expensive, has complex processes, and is difficult to construct. This type of cable with good fire resistance can be used in oil filling areas, important wooden public buildings, high-temperature places, and other places where fire resistance requirements are high and economic efficiency is acceptable. What issues should be paid attention to when selecting fire-resistant cables? According to the specific characteristics of fire-resistant cables, designers should pay attention to the following issues when designing and selecting: (1) When fire-resistant cables are used in cable tunnels and cable mezzanines with dense cables, or in flammable places such as oil pipelines and oil depots, Class A fire-resistant cables should be selected first. Except for the above situations and when the number of cables is small, Class B fire-resistant cables can be used. (2) Fire-resistant cables are mostly used as emergency power supply circuits. The editor reminds that they must work normally during fires. Since the ambient temperature rises sharply during fires, in order to ensure the transmission capacity of the line and reduce the voltage drop, for circuits with long power supply lines and strictly limited allowable voltage drops, the cross-section of the fire-resistant cable should be enlarged by at least one level. (3) Fire-resistant cables cannot be used as high-temperature resistant cables. (4) To reduce the probability of cable joint failure in fire accidents, the number of joints should be minimized during installation to ensure that the line can operate normally in a fire. If branch wiring is required, the joints should be properly fireproofed.
The above is the editor's introduction to fire-resistant wires and cables and the characteristics and benefits of fire-resistant cables. I hope it will be helpful to everyone. Here I would like to remind everyone that when purchasing cables, be sure to purchase cables with the "CCC" certification mark. Since wire and cable products are closely related to the lives of consumers, their quality and safety directly affect the personal and property safety of consumers.
