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Basic principles of selecting wires and cables

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In the selection of wires and cables, it is generally necessary to pay attention to the selection of wire and cable model and specification (conductor section).


1. Selection of wire and cable model


When selecting wires and cables, the purpose, laying conditions and properties should be considered; for example,


According to different uses, power cable, overhead insulated cable and control cable can be selected;


According to the different laying conditions, general plastic insulated cable, steel strip armored cable, steel wire armored cable and anticorrosive cable can be selected;


According to the requirements, non flame retardant cable, flame retardant cable, halogen-free flame retardant cable and fire-resistant cable can be selected.


2. Selection of wire and cable specifications


When determining the specification (conductor section) of wire and cable, the selection conditions such as heating, voltage loss, economic current density and mechanical strength should be considered


According to experience, the section of low-voltage power line is generally selected according to the heating conditions, and then the voltage loss and mechanical strength are checked; because the low-voltage lighting line has high requirements for voltage level, the section can be selected according to the allowable voltage loss condition, and then the heating condition and mechanical strength are checked; for the high-voltage line, the section is selected according to the economic current density first, and then the voltage loss and mechanical strength are checked The heating condition and allowable voltage loss should be checked, and the mechanical strength of high voltage overhead lines should also be calculated. If users have no experience, they should consult relevant professional units or persons.


explain:


1. The current carrying capacity of aluminum core conductor of the same specification is about 0.7 times of that of copper core conductor. The aluminum core conductor can be one size larger than the copper core conductor. The cross-linked polyethylene insulation can be of a smaller size, while the fire-resistant wire and cable should be larger.


2. The capacity calculated in this table is based on three-phase 380V, cos φ = 0.85. If single-phase 220V, cos φ = 0.85, the capacity should be × 1 / 3.


3. When the ambient temperature is high or the open laying method is adopted, the current carrying capacity will decrease, so the larger size should be selected; when the motor is used for frequent starting, 2-3 specifications should be selected. Overhead cable


4. PVC insulated wires in this table are calculated by single overhead laying mode. If they are laid through pipes or multiple cables, 2-3 specifications shall be selected


5. The above data are for reference only. The design and determination of cable model and specification shall refer to relevant information or electrician manual.


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