Because the cable is divided into high voltage cable, low voltage cable; Copper cable, aluminum cable; From the core number it has a single core, 2 core, 3 core, 4 core, 5 core; With insulating materials it has oil paper insulation, plastic insulation, rubber insulation; There are also compression armored cable and so on, so in the choice of cable learning is relatively large.

Here I use the commonly used three - phase four - wire system of low - voltage PVC power cable.

(1) the choice of cable must first consider the cable conductor allowable safe carrying capacity;

(2) the supply line distance allowable voltage loss value;

(3) cable wire mechanical strength;

Generally, the section area of the cable conductor is selected according to the allowable carrying capacity, and then checked with other conditions. If the cross-sectional area cannot meet the requirements of a certain check condition, the minimum allowable cross-sectional area that can meet the condition should be selected.

(1) select according to allowable carrying capacity. The allowable carrying capacity of the cable conductor is also known as the safe carrying capacity of the conductor or the safe current value of the conductor. The maximum allowable operating temperature of the general conductor is 65C. When the temperature exceeds this, the insulation layer of the conductor will accelerate the aging, or even deteriorate and damage and cause fire. The allowable carrying current of the conductor is the maximum current that can be passed for a long time when the working temperature of the conductor does not exceed 65C.

Since the operating temperature of the cable conductor is not only related to the current passing through the conductor, but also related to the heat dissipation condition and ambient temperature of the conductor, the allowable carrying capacity of the conductor is not a fixed value. When the same conductor is laid in different ways or at different ambient temperatures, its allowable carrying capacity is also different.

(2) according to mechanical strength. When the load is too small, the section area of the wire selected according to the allowable carrying capacity calculation will be too small, often unable to meet the requirements of mechanical strength, easy to break the wire accident. At this time the best choice of cable specifications model a few larger cable.

(3) select according to line allowable voltage loss. The voltage loss of power supply line is directly related to the distance of the line. That is to say, the voltage loss of the distance from the power distribution room to the load is usually 4% ~ 6%; If the line is too long, in the choice of power cable, you need to consider the choice of a model size of the cable can be.