When choosing wire and cable, attention should be paid to the selection of wire and cable types and specifications (conductor cross section).
            1. Selection of Wire and Cable Types            When choosing wires and cables, consideration should be given to their use, laying conditions and safety.
            According to different uses, power cables, overhead insulated cables and control cables can be selected.
            According to different laying conditions, general plastic insulated cables, steel tape armoured cables, steel wire armoured cables and anti-corrosion cables can be selected.
            According to safety requirements, non-flammable cable, flame-retardant cable, halogen-free flame-retardant cable, fire-resistant cable and so on can be selected.
            2. Selection of wire and cable specifications 
           When determining the specifications of wires and cables (conductor cross section), the selection conditions such as heating, voltage loss, economic current density and mechanical strength should generally be considered. According to experience, low-voltage power line usually chooses section according to heating condition because of its large load current, and then checks its voltage loss and mechanical strength; low-voltage lighting line, because of its high requirement for voltage level, can choose section according to the allowable voltage loss condition first, then checks its heating condition and mechanical strength; and high-voltage power line, because of its high requirement for voltage level, can choose section according to the allowable voltage loss condition. First, the section is selected according to the economic current density, then the heating condition and the allowable voltage loss of the cable machinery are checked, and the mechanical strength of the high voltage overhead lines should also be checked. If the user has no experience, he should consult the relevant professional units or
            Personal opinion.
            Explanation: 1. The current carrying capacity of the same specification aluminium-core conductor is about 0.7 times that of the copper-core conductor. The aluminium-core conductor is larger than the copper-core conductor, the crosslinked polyethylene insulator is smaller, and the refractory wire and cable is larger.
            3. The calculation capacity of this table is based on three-phase 380V and Cos_ phi=0.85. If single-phase 220V and Cos_ phi=0.85, the capacity should be *1/3.
            4. When the ambient temperature is high or the open application mode is adopted, the safe current carrying capacity will decrease. At this time, larger specifications should be selected; when used for frequent starting motor, larger 2-3 specifications should be selected.
            5. The PVC insulated wires in this table are calculated by single overhead laying method. If they are for pipe-piercing or multi-laying, 2-3 specifications should be selected.
            6. The above data are for reference only. The final design and determination of cable types and specifications should refer to relevant professional information or electrical manuals.
            Normal, and according to the cable type specifications, length and ambient temperature, the measurement results are corrected appropriately. Small size (solid conductor below 10mm 2) cables should also be measured whether conductors are on or off.
            6. When laying cables directly, attention should be paid to soil conditions. The depth of laying cables under general buildings is not less than 0.3 meters, and the surrounding environment is more complex, such as arable land, construction sites or roads, etc. A certain depth of laying (0.7-1 meters) should be required to prevent accidental damage to the buried cables. When necessary, the cables should be erected clearly. A marked sign.