Ordinary wires and cables
1. The applicable temperature range of ordinary PVC wire and cable is - 15 ℃ ~ 60 ℃, and special PVC wire and cable shall be used when the ambient temperature of the place of use exceeds the range; ordinary PVC wire and cable will emit toxic smoke when burning, which is not suitable for underground passenger transport facilities, underground commercial areas, high-rise buildings, important public facilities and other densely populated places.
2. XLPE wires and cables do not have flame-retardant properties, but will not produce a lot of toxic fumes when burning. They are suitable for industrial and civil buildings with "clean" requirements.
3. Rubber wire and cable have good bending performance and can be laid in severe cold climate, suitable for places with large horizontal height difference and vertical laying; rubber wire and cable are suitable for power supply lines of mobile electrical equipment.
Flame retardant wire and cable
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 performance of the flame retardant cable with the residual flame and the residual ignition can be extinguished by themselves within the limited time is mainly evaluated by two indexes of oxygen index and smoke emission. Because oxygen accounts for 21% in the air, the materials with oxygen index more than 21 will self extinguish in the air. The higher oxygen index is, the better the flame retardancy is. 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. For directly buried cables, cables directly buried in building holes or masonry, and wires and cables laid through pipes, ordinary wires and cables can be selected. If the cable laid in the cable trench with cover box and cover plate has been blocked, blocked from water, isolated and other measures to prevent delayed combustion, the requirements of class I flame retardant can be reduced.
Fire resistant wire and cable
1. Fire resistant wires and cables refer to the normal operation characteristics that can be maintained in the flame for a certain period of time under the specified test conditions
2. According to the insulation material, the fire-resistant cable can be divided into two types: model and non model. For some models, mica tape with high temperature resistance of 800 ℃ is mainly used to cover two layers with overlapping coverage rate of 50% as the fire-resistant layer; PVC or XLPE is used as the external insulation, if flame-retardant is required at the same time, as long as the insulation material is flame-retardant. The fire-resistant cable can withstand 950 ℃ high temperature after being added with oxygen barrier. No machine is mineral insulated cable. It is a kind of cable with magnesium oxide as insulation material and copper tube as sheath. It is internationally known as Mi cable.
3. Fire resistant wires and cables are mainly applicable to the lines that still need to keep normal operation in case of fire.
4. The fire resistance rating shall be determined according to the possible flame temperature during the fire.
Selection of section 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, it shall not exceed the allowable short-circuit strength. The high-voltage cable shall be verified for thermal stability, and the bus shall be verified for dynamic and thermal stability.
3. The voltage loss is within the allowable range.
4. Meet the requirements of mechanical strength.
5. The 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.