In electrical engineering design, the reasonable selection of conductor diameter is a key link to ensure the safe, stable, and economic operation of the power system. Improper selection of conductor diameter not only may lead to line overheating and fire, but also may cause excessive voltage drop, affecting the normal operation of equipment, and even increase energy consumption. Therefore, in the process of electrical design, it is necessary to scientifically and systematically select the conductor diameter.



1. Basic principles of conductor selection



The selection of conductor diameter mainly depends on the following basic principles:



1. Load current requirements: The conductor should be able to safely carry the normal working current without overheating. The load current is closely related to factors such as conductor material (such as copper or aluminum), insulation type, laying method (such as exposed, conduit or buried), and environmental temperature.



2. Control of voltage loss: In long-distance power supply lines, the resistance of the wire will cause voltage drop, and excessive voltage drop will affect the normal operation of the equipment. It is usually required that the voltage drop of the line does not exceed 5% of the rated voltage.



3. Requirements for mechanical strength: The wire should have sufficient mechanical strength to withstand the tension during installation and the wind, snow, and ice loads during long-term operation.



4. Consideration of economy: Achieve a balance between the investment in the line and the operation cost, avoid blind increase in wire diameter to cause waste, and also avoid the increase in maintenance and energy consumption costs due to too small wire diameter.



Two, the main steps of wire diameter selection



1. Determine the load current



According to the power and voltage of the electrical equipment, calculate the working current of the line. The formula is:



$$

　　I = \frac{P}{\sqrt{3} \cdot U \cdot \cos\varphi}



$$



Among them, $I$ is the current; $P$ is the active power; $U$ is the line voltage; $\cos\varphi$ is the power factor.



2. Preliminary selection of wire diameter



According to the load current, refer to the national standard GB/T 16895 or the 'Design Code for Low-Voltage Distribution' for the allowable current of wires under different laying methods to preliminarily select the wire diameter.



3. Verify voltage loss



The calculation formula for voltage loss is:



$$



\Delta U = \frac{I \cdot L \cdot R}{1000}



$$



Among them, $L$ is the length of the line (km), and $R$ is the resistance per unit length (Ω/km). If the calculated result exceeds the allowable value, the wire diameter should be increased.



4. Verify mechanical strength



For overhead lines or outdoor lines, it is necessary to verify whether the wire meets the minimum cross-sectional area requirements to prevent wire breakage due to mechanical stress.



5. Consider short-circuit protection coordination



The selected wire should also be matched with the upper-level protective electrical appliances (such as fuses, circuit breakers) to ensure that the power supply can be cut off in time during short-circuit or overload conditions, preventing the fault from expanding.



Three, Matters to be noted in practical applications



- In residential and commercial buildings, copper-core wires are generally used due to their good conductivity and strong corrosion resistance.



- For long-distance transmission lines, it is preferred to use larger cross-sectional area wires to reduce energy loss.



- In high-temperature, humid, or dusty environments, it is necessary to select high-temperature-resistant, flame-retardant, or corrosion-resistant wires.



- When multiple wires are connected in parallel, attention should be paid to the uniformity of current distribution, and it is necessary to use wires of the same specification when required.

　　Four, Summary

　　The selection of wire diameter is a fundamental and critical task in electrical design, which must comprehensively consider safety, economy, and practicality. Designers should scientifically and reasonably select wire types based on specific engineering conditions, in conjunction with relevant specifications and standards, to ensure the long-term stable operation of the electrical system. With the development of intelligent buildings and the concept of green energy saving, the future selection of wire types will also pay more attention to the combination of energy saving, consumption reduction, and intelligent management.