1. Determine the Required Current Rating
- Identify the maximum continuous current (Amperes) the busbar needs to carry.
2. Calculate the Cross-Sectional Area (A)
- Method 1: Rule of Thumb
- This is a common starting point for general-purpose busbars.
- A widely used rule is 1 Ampere per 1 square millimeter (mm²) for copper busbars, though this can be adjusted based on specific applications and tolerances.
- Method 2: Thermal Stress (for Short-Circuit)
- This formula is used when the busbar must withstand a fault current for a specified duration.
- Formula:
A = √(I² x t) / k- A: Cross-sectional area (mm²)
- I: Fault current (A)
- t: Fault duration (seconds)
- k: Material constant (e.g., Copper: 205, Aluminum: 126)
3. Select Standard Dimensions (Width and Thickness)
- Once the required cross-sectional area (A) is determined, select a standard busbar size by finding a combination of width and thickness that provides the calculated area.
- For example, if you need an area of 100 mm², you could choose a 10 mm x 10 mm busbar, or a 20 mm x 5 mm busbar.
4. Consider Derating Factors and Other Design Considerations
- Derating Factors:
Apply derating factors for factors like ambient temperature, grouping of busbars, and ventilation to adjust the current carrying capacity. - Electromagnetic Forces:
For high currents, calculate the forces between busbar phases and ensure the supports can withstand these forces. - Material & Standards:
Always refer to relevant industry standards (e.g., IEC 61439, IS 808) and select appropriate materials like copper or aluminum based on cost and conductivity. - Panel/Enclosure Design:
Consider how the busbar will be mounted and how its shape (width/height ratio) affects inductance and capacitance.
