1. NH cables only have mica tape wrapped around the conductor! ZBN cables have mica tape wrapped around the conductor, and rubberized cloth tape should be wrapped around the conductor during the cabling process. Multi-core cables also require mineral paper rope filling, and the flame-retardant sheathing material should be highly flame-retardant with an oxygen index greater than 35.
2. "Test Methods for Fire Resistance of Wires and Cables" (GB12666.6-90) stipulates: Class A: 950-1000°C, 90 minutes; Class B: 750-800°C, 90 minutes. IEC331-1970 stipulates 750°C, 3 hours, equivalent to my country's Class B standard. The new draft of IEC60331, recently submitted for voting by the IEC, maintains the fire temperature of 750-800°C, 3 hours. If this standard is adopted in my country, it will be adopted as such, and there will be no Class A or B distinction for fire-resistant cables. 3. Fire-resistant wires and cables can be divided into flame-retardant and non-flame-retardant types based on their non-metallic materials. Domestic fire-resistant wires and cables primarily feature mica-coated conductors and extruded flame-retardant sheaths, with the majority being Class B products. Currently, those that meet Class A standards include those using special synthetic mica tape and mineral-insulated (copper core, copper sheath, magnesium oxide insulation, also known as MI) fire-resistant cables. Mineral-insulated fire-resistant cables are non-flammable, smokeless, corrosion-resistant, non-toxic, and impact- and spray-resistant, making them considered fire-resistant. Their fire resistance is the most outstanding among fire-resistant wires and cables, but they require a complex manufacturing process, resulting in higher prices, limited lengths, large bend radii, and moisture-sensitive insulation. Currently, only single-core products with cross-sections of 25 mm² and above are available, requiring the use of permanent, dedicated terminals and intermediate connectors, making installation and construction complex.
The key difference is that NH indicates that the cable has fire resistance, while ZBN indicates that the cable has flame retardant properties in addition to fire resistance. For details, please refer to GB/T 19666-2005.
