Busbar Design Calculation for Electrical Panels
Busbars are critical components in switchgear, MCC panels, and distribution boards. A correct busbar design calculation ensures safety, efficiency, and long service life. This article explains how to calculate busbar size with formulas and examples.
Step 1 – Determine Busbar Current
The current carrying capacity of busbar is calculated as:
I = P / (√3 × V × PF × Î·)- P = Power in kW
- V = Voltage (line-to-line)
- PF = Power Factor
- η = Efficiency
Step 2 – Cross Section Area
For copper, assume 1.2 to 1.5 A per mm². For aluminum, assume 0.8 A per mm².
Step 3 – Busbar Sizing Example
A 250 kW motor at 415V, PF = 0.85, η = 0.95
I = 250,000 / (√3 × 415 × 0.85 × 0.95) ≈ 450 AFor copper: Required area = 450 / 1.2 ≈ 375 mm² Choose 2 strips of 25 × 8 mm = 400 mm²
Standard Busbar Sizes
| Current (A) | Copper Size (mm) | Aluminum Size (mm) |
|---|---|---|
| 200 | 25 × 6 | 32 × 6 |
| 400 | 25 × 10 | 40 × 8 |
| 800 | 2 × (40 × 10) | 2 × (50 × 10) |
FAQ – Busbar Design
Q1: Which is better, copper or aluminum busbar?
Copper has higher conductivity but aluminum is cheaper and lighter.
Q2: Why are multiple strips used instead of one thick busbar?
To improve cooling and reduce skin effect losses.
Q3: What standards apply to busbar design?
IEC 61439 and IS 8623 standards are commonly followed.
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