Common specifications and conditions of use of fire-resistant wire and cable

Fire-resistant wires and cables mainly refer to cables that can continue to work normally and safely for a certain period of time under the condition of flame burning. Fire-resistant wires and cables can maintain normal power supply for a period of time when a fire occurs. This feature determines that fire-resistant wires and cables play an important role in modern urban and industrial buildings, because once a fire occurs, control, monitoring, guidance and alarm systems The power supply circuit must maintain normal operation. Therefore, fire-resistant wires and cables are mainly used in places and occasions that are closely related to fire safety, such as high-rise buildings, underground streets, large power stations, and important industrial and mining enterprises.

1.Conditions of use of fire-resistant wire and cable

(1) Maximum working temperature

a.Resisting polyvinyl fluoride insulation and sheath: 70°C and 105°C
b.XLPE insulation: 90°C;
c.Fluoroplastic insulation and sheath: 220°C and 260°C
d.Fluoroplastic insulation and 105°C flame-retardant polyvinyl fluoride sheath: 90°C and 125°C
e.Low-halogen, low-smoke, flame-retardant PVC insulation and sheath: 70°C
f.Halogen-free low-smoke flame-retardant polyolefin insulation and sheath: 90°C and 125°C

(2) Minimum working temperature

a.Flame-retardant PVC insulation and sheath: fixed laying -40°C; non-fixed laying -15°C
b.Fluoroplastic insulation and sheath: fixed laying -60°C; non-fixed laying -20°C

(3) Allowable bending radius for laying

Unarmored and braided shielded cables should not be less than 6 times the outer diameter of the cable; steel tape armored cables should not be less than 12 times the outer diameter of the cable;

Fluoroplastic insulation and sheath material cables should not be less than 8 times the outer diameter of the cable.

2.Common models of fire-resistant wire and cable

(1) NA-YJV/NB-YJV: XLPE insulated PVC sheathed fire-resistant power cables, which can be laid in indoors, tunnels and pipelines that require fire resistance.

(2) NA-YJV22/NB-YJV22: Cross-linked polyethylene insulated steel tape armored PVC sheathed fire-resistant power cable, suitable for buried laying when fire resistance is required, not suitable for laying in pipelines.

(3) WDNA-YJY/WDNB-YJY: Cross-linked polyethylene insulated polyolefin sheathed halogen-free low-smoke fire-resistant power cables can be laid in indoors, tunnels and pipelines that require halogen-free, low-smoke and fire resistance.

(4) WDNA-YJY23/WDNB-YJY23: cross-linked polyethylene insulated steel tape armored polyolefin sheathed halogen-free low-smoke fire-resistant power cable, suitable for buried laying when there are requirements for halogen-free, low-smoke and fire resistance, not suitable for pipelines laying inside.

3.How to choose fire-resistant wire and cable?

(1) When fire-resistant cables are used in cable tunnels and cable interlayers with dense cables, or in flammable places such as oil pipes and oil depots, Class A fire-resistant cables should be selected first. Under the flame and rated voltage, withstand burning for at least 90 minutes, so that the cable will not be broken down. In addition to the above circumstances and when the number of cables is small, Class B fire-resistant cables can be used. Class B fire-resistant cables can withstand burning for at least 90 minutes in a flame of 750 ° C ~ 800 ° C and rated voltage without the cable being broken down. Class A fire-resistant cables The difference from Class B fire-resistant cables lies in the difference in fire-resistant temperature.

(2) Fire-resistant cables are mostly used as power supply circuits for emergency power supplies, and can work normally within a certain period of time when a fire occurs. Since the ambient temperature rises sharply during a fire, in order to ensure the transmission capacity of the line and reduce the voltage drop, for circuits with long power supply lines and strict limits on the allowable voltage drop, the section of the fire-resistant cable should be enlarged by at least one gear.

(3) Fire-resistant cables cannot be used as high-temperature resistant cables, and the two are essentially different in terms of use.

(4) In order to reduce the failure probability of cable joints in fire accidents, the number of joints should be reduced as much as possible during installation to ensure that the lines can work normally in a fire. If branch wiring is required, the joints should be treated with fire protection.