The issue of power system interruptions caused by power cable fires is gaining increasing attention. Therefore, in some locations with extensive cable installations and industries with a large number of electrical equipment, a combination of fire-resistant and flame-retardant cables is being used. However, in actual use, many people confuse the concepts behind these cables and have a vague understanding of their structures and performance. For proper use, it's crucial to understand the concepts and differences between fire-resistant and flame-retardant cables.
Overview of Flame-Retardant and Fire-Resistant Cables
1) Flame-Retardant Cable
This refers to a cable that, under specified test conditions, burns within a specified range. After the test fire source is removed, the flame spreads only within a specified range, and any residual flames or burns self-extinguish within a specified time.
Its fundamental characteristic is that while it may be damaged and rendered inoperable in a fire, it can prevent the spread of fire. In simple terms, in the event of a cable fire, the fire is confined to a specific area, preventing it from spreading, thus protecting other equipment and preventing further damage.
2) Fire-Resistant Cable
This refers to a cable that can maintain safe operation for a specified period of time under flame conditions.
Its fundamental characteristic is: the ability to operate continuously under specified conditions when burning under specified fire sources and time, that is, the ability to maintain line integrity.
Differences between fire-resistant cables and flame-retardant cables
1 Differences in principles
The principles of fire-resistant cables and flame-retardant cables are different. The flame-retardant principle of halogen-containing cables relies on the flame-retardant effect of halogens, while the flame-retardant principle of halogen-free cables relies on the precipitation of water to lower the temperature to extinguish the fire. Fire-resistant cables rely on the fire-resistant and heat-resistant properties of the mica material in the fire-resistant layer to ensure that the cable can work normally even in a fire.
2 Differences in structure and materials
The structure and materials of fire-resistant cables are also different from those of flame-retardant cables.
The basic structure of flame-retardant cables is:
(1) The insulation layer is made of flame-retardant materials
(2) The sheath and outer sheath are made of flame-retardant materials;
(3) The wrapping tape and filling are made of flame-retardant materials.
Fire-resistant cables typically have a fire-resistant layer between the conductor and the insulation. While theoretically, adding a fire-resistant layer to a flame-retardant cable would create a cable that's both flame-retardant and fire-resistant, this isn't necessary in practice.
The fire-resistant layer of fire-resistant cables, typically made of multiple layers of mica tape wrapped directly around the conductor, withstands prolonged combustion, ensuring normal operation even if the polymer in the area of the flame is destroyed.
The importance of cable fire protection is growing, and the distinction between fire-resistant and flame-retardant cables is becoming increasingly common in water conservancy and hydropower applications. Therefore, special attention should be paid to their differing characteristics during use. We hope this article will provide a foundation for power system designers to make informed choices and help those unfamiliar with the concepts of these two types of cables gain a deeper understanding.
