Today, I'll introduce you to fire-resistant cables. Those with some familiarity with cables and wires should know that there are many different types of fire-resistant cables. Fire-resistant cables are cables that can maintain safe operation for a certain period of time under flame conditions. It's no surprise that these cables have many practical features and are also classified. I'll discuss these two points below.
Fire-resistant cables are cables that can maintain safe operation for a certain period of time under flame conditions. my country's national standard GB12666.6 (and IEC331) divides fire resistance tests into two levels: A and B. Level A requires a flame temperature of 950-1000°C for a continuous fire duration of 90 minutes, while Level B requires a flame temperature of 750-800°C for a continuous fire duration of 90 minutes. During the entire test period, the test specimen must withstand the product's specified rated voltage. Fire-resistant cables are widely used in high-rise buildings, subways, underground shopping malls, large power stations, and important industrial and mining enterprises, where fire safety and lifesaving measures are crucial. For example, they serve as power supply and control lines for firefighting equipment and emergency guidance lights.
I. Fire-Resistant Cable Usage Characteristics
1. Power frequency rated voltage U0/U: 0.6/1kV.
2. Maximum allowable long-term operating temperature of cable conductor:
Flame-retardant polyvinyl chloride: 70°C/105°C.
Cross-linked polyethylene: 90°C.
3. The ambient temperature during cable installation should be no less than 0°C.
4. Cable bending radius:
Power cable: ≥40D for single-core cables, ≥30D for multi-core cables, ≥12D for control cables.
B-series plastic wire: ≥4D (for cable diameters less than 25mm), ≥6D (for cable diameters greater than 25mm).
5. Fire-resistant cable outer diameter ratio: 15% larger than standard comparable models for cross-sections under 25mm²; 25% larger than standard comparable models for cross-sections greater than 25mm².
6. The product's electrical performance, physical and mechanical properties, and current carrying capacity are the same as those of ordinary products.
7. The fire resistance test standard is IEC 331 or GB 12666.6.
II. Fire-Resistant Cable Classification
Fire-resistant cables are classified into four grades:
Grade 1: NH-IA
NH-IB
Grade 2: NH-IIA
NH-IIB
Grade 3: NH-IIIA
NH-IIIB
Grade 4: NH-IVA
NH-IVB
Grade A indicates a fire resistance test flame temperature of 950-1000°C and a continuous fire duration of 90 minutes.
Grade B indicates a fire resistance test flame temperature of 750-800°C and a continuous fire duration of 90 minutes.
Although it is called a cable, fire-resistant cables cannot be used as high-temperature cables. This is something we must understand. Among them, NA-YJV/NB-YJV, NA-YJV22/NB-YJV22, WDNA-YJY/WDNB-YJY, WDNA-YJY23/WDNB-YJY23 are all fire-resistant cables, but the difference is that their uses may be slightly different.
