Let's discuss with industry colleagues whether fire-resistant cables are necessarily flame-retardant. Let's examine the differences between fire-resistant and flame-retardant cables.
1. Are fire-resistant cables necessarily flame-retardant?
The answer is no. There are two types of fire-resistant cables. The first is the organic type, which relies entirely on a mica layer for fire resistance and uses polyvinyl chloride or cross-linked polyethylene for insulation. This type of cable is not necessarily flame-retardant. The second type is the true fire-resistant MI cable, which uses magnesium oxide as insulation and a copper tube as a sheath. As long as the flame does not exceed the melting point of copper, 1083°C, the cable is safe. This type of cable is smokeless, non-toxic, flame-retardant, and fire-resistant.
2. What type of cable is flexible cable?
Flexible cables (with Chinese characteristics) are essentially the first type of organic cable. Through process improvements, they can achieve the characteristics of the second type of MI cable under experimental conditions. However, real-world conditions are more complex and may not meet the requirements.
The choice of flexible mineral insulated cable is determined by the design requirements of the construction project. Each type of mineral insulated cable has its advantages and disadvantages, and these deficiencies are the reason for continuous improvement and refinement. Generally, the price of flexible mineral fire-resistant cables is YTTW > BTLY > BBTRZ. Installation is becoming increasingly simple, and all types can pass fire protection system inspections. Therefore, a third-party professional evaluation report is required to determine the appropriate model.
3. Flame-retardant Cable Model Marking
One is the old marking system, WDZA, WDZB, WDZC, and WDZD, derived from GB/T19666.
The other is the new cable specification, which uses flammability performance A, B1, and B2, derived from GB31247.
These two types have different evaluation requirements, testing environments, and methods. The latter is closer to the requirements of actual fire environments.
The Difference Between Fire-Resistant and Flame-Retardant Cables
1. Terms and Definitions of Fire-Resistant and Flame-Retardant Cables
1) Flame Retardancy
Under specified test conditions, when a specimen is burned, the flame spreads within a limited range and extinguishes itself after the fire source is removed. This indicates the ability to prevent or delay the occurrence or spread of flames.
2) Fire Resistance
The ability to continuously operate under specified conditions when burned under a specified fire source and duration, indicating the ability to maintain line integrity.
2. Differences in the Principles of Fire-Resistant and Flame-Retardant Cables
The flame retardancy of halogen-containing cables is due to their flame retardant effect, while the flame retardancy of halogen-free cables is due to their temperature reduction. The principle of fire-resistant cables is mica.
3. Differences in structure and materials between fire-resistant cables and flame-retardant cables
Basic structure of flame-retardant cables:
(1) Insulation layer
(2) Sheath and outer sheath
(3) Tape and filling
A fire-resistant layer is added between the conductor and the insulation layer of fire-resistant cables, which can withstand long-term burning and ensure the normal operation of the line.
4. Advantages and disadvantages of fire-resistant cables and flame-retardant cables
Features of flame-retardant cables: low cost, control the spread of flames within a certain range, and improve the fire protection level of cable lines.
Fire-resistant cables: generate less acid gas smoke, greatly improve fire resistance and flame retardancy, and maintain the integrity of the line. 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. Relatively speaking, the price of fire-resistant cables will be more expensive.
