How to calculate the current-carrying capacity of the copper busbars in the distribution box?

The calculation of the current-carrying capacity of the copper busbars in the distribution box needs to comprehensively consider factors such as the cross-sectional area of the copper busbars, the ambient temperature, and the installation method. The following are the specific steps and precautions: ### I. Core Factors Affecting the Current-Carrying Capacity 1. **Cross-sectional Area of Copper Busbars**   - The larger the cross-sectional area, the higher the current-carrying capacity (related to the current density, usually taking 2-5A/mm², specifically depending on the heat dissipation conditions). 2. **Ambient Temperature**   - The higher the ambient temperature, the lower the current-carrying capacity (a correction coefficient is required). 3. **Installation Method**   - Single-row, double-row or multi-layer arrangement will affect the heat dissipation efficiency. 4. **Insulation Layer**   - The copper busbars with an insulation layer have poor heat dissipation, and the current-carrying capacity needs to be appropriately reduced. ### II. Theoretical Calculation Methods #### 1. Formula Method The estimation formula for the current-carrying capacity \(I\) is: \[ I = K \cdot S \cdot \sqrt{\Delta T} \] - \(K\): Coefficient (take 1.2-1.5 for copper busbars). - \(S\): Cross-sectional area (mm²). - \(\Delta T\): Allowable temperature rise (°C, usually take 60°C). **Example**: For a copper busbar with a cross-sectional area of 100mm² and an allowable temperature rise of 60°C, then \(I \approx 1.3\times100\times\sqrt{60} \approx 1.3\times100\times7.75 \approx 1008A\). #### 2. Empirical Formula (When the Ambient Temperature is 30°C) - For single-row copper busbars: \(I \approx 1.5\times S\) (A). - For double-row copper busbars: \(I \approx 2.5\times S\) (A). **Example**: The current-carrying capacity of a 50mm² single-row copper busbar is approximately \(1.5\times50 = 75A\). ### III. Method of Looking up Tables in Practical Applications Directly look up the current-carrying capacity table of copper busbars provided by standard manuals or manufacturers. The reference for common specifications is as follows:

**Note**: The data in the table is based on an ambient temperature of 30°C, without an insulation layer, and horizontal installation. ### IV. Temperature Correction Coefficient If the ambient temperature exceeds 30°C, it needs to be corrected according to the following coefficient: \[ \text{Correction Coefficient} = \sqrt{\frac{90 - T}{60}} \] - \(T\): Actual ambient temperature (°C). - **Example**: When the ambient temperature is 40°C, the correction coefficient is \(\sqrt{\frac{90 - 40}{60}} \approx 0.91\), and the current-carrying capacity needs to be multiplied by 0.91. ### V. Precautions 1. **Safety Factor**   - In practical applications, it is recommended to select 80%-90% of the calculated value to reserve an overload margin. 2. **Heat Dissipation Conditions**   - Vertical installation has better heat dissipation than horizontal installation, and the current-carrying capacity can be appropriately increased. 3. **Influence of Plating Layer**   - Tinned copper busbars can improve corrosion resistance, but the current-carrying capacity is slightly lower than that of bare copper busbars (approximately reduced by 5%-10%). 4. **Parallel Connection of Multiple Busbars**   - When multiple copper busbars are connected in parallel, the problem of uneven current distribution needs to be considered for the total current-carrying capacity (it is recommended not to connect more than 3 busbars in parallel). ### VI. Summary 1. **Give Priority to Looking up Tables**: Directly use the standard current-carrying capacity table (such as the "Code for Design of Low-voltage Power Distribution" GB 50054). 2. **Accurate Calculation**: In complex scenarios, comprehensively evaluate by combining formulas, temperature correction, and heat dissipation conditions. 3. **Safe Design**: Reserve a margin to avoid excessive temperature rise or insulation aging caused by the overload of copper busbars. It is recommended that electrical engineers conduct calculations according to the specific design requirements of the distribution box and local standards.