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Intro. Understanding the AC cable selection standards is the crucial first step to ensure the safe and stable operation of the power system.
In a power system, the selection of AC cables is a vital and meticulous task. It not only affects the safe and stable transmission of electricity but also impacts the cost and efficiency of the entire power project. So, what are the key standards for AC cable selection? Let's delve into it.
I. Current Carrying Capacity (Ampacity)
Basis for Ampacity Calculation
Ampacity refers to the maximum current value that a cable can continuously carry without exceeding its maximum operating temperature. Its calculation needs to consider multiple factors, such as the material of the cable (copper core or aluminum core), the heat resistance level of the insulation material, the laying method (laid in air, directly buried, laid in a pipe, etc.), and the ambient temperature. For example, copper core cables usually have a higher ampacity than aluminum core cables because copper has better electrical conductivity. Moreover, in a high-temperature environment, the ampacity of the cable will decrease accordingly, which requires us to adjust the selection according to the actual ambient temperature.
Importance of Matching with the Load
In practical applications, it is necessary to ensure that the ampacity of the selected cable is greater than or equal to the actual load current. If the cable's ampacity is too small, it will cause the cable to overheat, accelerate insulation aging, and even lead to serious safety accidents such as fire. This is like making a small horse cart pull a weight beyond its carrying capacity, and it will eventually be damaged under the heavy load.
II. Voltage Level
Applicable Ranges of Cables with Different Voltage Levels
AC cables have various voltage levels, such as low voltage (1kV and below), medium voltage (1kV - 35kV), and high voltage (35kV - 110kV), etc. Cables of different voltage levels are applicable to different power transmission scenarios. Low-voltage cables are commonly used for power distribution within buildings, such as household electricity and commercial electricity; medium-voltage cables are widely used in urban distribution networks to connect substations and distribution boxes in various areas; high-voltage cables are mainly used for long-distance and large-capacity power transmission, such as transmission lines between cities and output lines of large power plants.

Key Points in Voltage Level Selection
When selecting, the cable with the corresponding voltage level must be chosen according to the actual voltage requirements of the power system. If the voltage level is not selected properly, it may cause the cable insulation to be broken down, resulting in power failure and affecting the reliability of power supply. This is like choosing the right foundation stone for buildings of different heights. Choosing the wrong one will make the building (power system) shaky.
III. Insulation Performance
Types and Characteristics of Insulation Materials
Common insulation materials for AC cables include polyvinyl chloride (PVC), cross-linked polyethylene (XLPE), ethylene propylene rubber (EPR), etc. PVC insulated cables have a relatively low price and are suitable for general low-voltage and normal temperature environments; XLPE insulated cables have excellent electrical and heat resistance properties and are widely used in medium and high-voltage cables; EPR insulated cables perform well in aging resistance and ozone resistance and are often used in some special environments or occasions with high requirements for cable performance.
Importance of Insulation Performance and Considerations in Selection
Good insulation performance is the key to ensuring the safe operation of the cable. When selecting, appropriate insulation materials should be chosen according to the specific usage environment and requirements of the power system. For example, in a humid environment with corrosive gases, an insulation material with good corrosion resistance should be preferred to prevent the cable's insulation performance from degrading and causing safety hazards such as electric leakage. This is like putting on suitable protective clothing for soldiers. Only with proper protection can they fight (operate) safely in various harsh environments.
IV. Mechanical Strength
Factors Affecting Mechanical Strength
The mechanical strength of a cable is mainly affected by its structure and material. For example, armored cables have a high resistance to external force damage due to the metal armor layer on the outside, and are suitable for laying environments where mechanical damage may occur, such as direct underground burial and crossing roads; while ordinary non-armored cables are more suitable for laying in relatively safe environments such as cable trays or indoors. In addition, the larger the cross-sectional area of the cable conductor, the relatively higher the mechanical strength, but the cost will also increase, so comprehensive consideration is required.
Selecting Cables with Appropriate Mechanical Strength According to the Laying Environment
In actual projects, cables with corresponding mechanical strength should be selected according to the laying environment of the cable. If a cable with insufficient mechanical strength is selected in an environment prone to external force damage, it may lead to the cable being squeezed, stretched, or even broken, affecting the power supply. This is like choosing the right tires for different road conditions. Choosing the wrong tires may cause the vehicle (power transmission) to "break down" halfway.
Three-phase 380V Asynchronous Motor Power Cable Selection Reference Table
Current (A) Copper Core Cable Size (mm²) Aluminum Core Cable Size (mm²)
≤20 2.5 4
20 - 30 4 6
30 - 45 6 10
45 - 60 10 16
60 - 85 16 25
85 - 110 25 35
110 - 145 35 50
145 - 180 50 70
180 - 220 70 95
220 - 260 95 120
260 - 300 120 150

Precautions
The above selection table is only a general reference. In actual selection, various factors mentioned above and specific usage conditions of the cable need to be comprehensively considered.
In a three-phase 380V system, due to factors such as power factor, for some special cases like high-power inductive loads, the cable size may need to be appropriately enlarged to ensure safe operation.
The selection of AC cables is a comprehensive process that requires comprehensive consideration of various standards such as ampacity, voltage level, insulation performance, and mechanical strength. Only in this way can reliable support be provided for the safe and stable operation of the power system, allowing electricity to flow smoothly to every corner where it is needed like blood.