Ordinary wire and cable
1. The applicable temperature range of ordinary PVC wire and cable is - 15 ℃~60 ℃. When the ambient temperature of the place of use exceeds this range, special PVC wire and cable shall be used; Ordinary PVC wires and cables will emit toxic smoke when burning. It is not suitable for densely populated places such as underground passenger transport facilities, underground commercial areas, high-rise buildings and important public facilities.
2. Cross-linked polyvinyl chloride (XLPE) wires and cables do not have flame retardancy, but will not produce a large amount of toxic smoke when burning, and are applicable to industrial and civil buildings with "clean" requirements.
3. Rubber wires and cables have good bending performance and can be laid in severe cold weather, suitable for places with large horizontal height difference and vertical laying; Rubber wires and cables are applicable to power supply lines of mobile electrical equipment.
Flame retardant wire and cable
The flame-retardant cable refers to the cable that is burned under the specified test conditions and can make the flame spread only within the limited range. After the fire source is removed, the residual flame and residual burning can be extinguished within the limited time. The performance of the flame-retardant cable is mainly evaluated by the oxygen index and smoke generation. Since oxygen in the air accounts for 21%, materials with oxygen index more than 21 will self-extinguish in the air. The higher the oxygen index of the material, the better its flame retardance. Flame retardant cables can be divided into general flame retardant cables, low smoke and low halogen flame retardant cables and halogen-free flame retardant cables according to the smoke characteristics during combustion. Ordinary wires and cables can be used for directly buried cables, cables directly buried in building holes or masonry, and wires and cables laid in pipes. For the cables laid in the cable trench with cover box and cover plate, if the measures such as blocking, water blocking and isolation have been taken to prevent delayed combustion, the requirements for Class I flame retardance can be reduced.
Fire-resistant wire and cable
1. Fire-resistant wires and cables refer to the normal operation characteristics that can be maintained for a certain period of time in the flame under the specified test conditions
Cable.
2. Fire-resistant cables can be divided into two types according to the insulation material: model and non-model. Some models mainly use mica tape with high temperature resistance of 800 ℃ to cover two layers with 50% overlap as the refractory layer; PVC or cross-linked polyethylene shall be used for external insulation. If flame retardant is required at the same time, flame retardant materials shall be selected as the insulation material. With the addition of the oxygen barrier, the fire-resistant cable can withstand the high temperature of 950 ℃. No model is mineral insulated cable. It is a cable with magnesium oxide as insulating material and copper tube as sheath, which is internationally known as MI cable.
3. Fire-resistant wires and cables are mainly applicable to the lines that still need to maintain normal operation in case of fire.
4. The fire resistance rating shall be determined according to the possible flame temperature in case of fire.
Selection of sectional area
1. When passing the load current, the core temperature shall not exceed the allowable long-term working temperature of wire and cable insulation.
2. When passing the short-circuit current, the allowable short-circuit strength shall not be exceeded. The thermal stability of the high-voltage cable shall be verified, and the dynamic and thermal stability of the bus shall be verified.
3. The voltage loss is within the allowable range.
4. Meet the requirements of mechanical strength.
5. Low-voltage wires and cables shall meet the requirements of load protection, and the TNT system shall also ensure that the protective apparatus can disconnect the circuit in case of ground fault.