How to Calculate Copper Busbar Size

1. What Is a Copper Busbar

A copper busbar is a metallic conductor, usually in the form of a flat strip or bar, used in electrical panels, switchgear, battery banks, and power distribution systems to carry and distribute electrical current. Copper is preferred for its high conductivity, excellent thermal performance, and durability.

Related types:

• Flexible Copper Busbar – Laminated or braided design for flexible applications.

• Solid Copper Busbar – Rigid structure for industrial panels.

• Insulated Busbar – Coated with PVC or epoxy for safety in compact layouts.

2. Why Correct Copper Busbar Sizing Is Important

Proper sizing ensures:

1. Current Carrying Capacity: Prevents overheating and maintains safe operation.

2. Minimized Voltage Drop: Ensures stable voltage across circuits.

3. Reduced Energy Loss: Optimizes efficiency and reduces operational costs.

4. System Reliability: Enhances lifespan of electrical equipment and reduces maintenance.

Common applications: electrical panels, battery busbar connections, EV battery packs, switchgear, and renewable energy systems.

3. Copper Busbar Calculation Formula

The general formula to calculate the cross-sectional area (A) of a copper busbar is:

$$\mathrm{<span\; style="font-size:\; 16px;">A</span>}<span\; style="font-size:\; 16px;">=</span>\frac{\mathrm{<span\; style="font-size:\; 16px;">I</span>}}{\mathrm{<span\; style="font-size:\; 16px;">k</span>}<span\; style="font-size:\; 16px;">\cdot </span>\mathrm{<span\; style="font-size:\; 16px;">\Delta </span>}\mathrm{<span\; style="font-size:\; 16px;">T</span>}}$$A = \frac{I}{k \cdot \Delta T}A=k⋅ΔTI

Where:

• A = Cross-sectional area of the busbar (mm²)

• I = Design current (Amps)

• k = Material constant based on conductivity and cooling (for copper, typically 0.024–0.029)

• ΔT = Allowable temperature rise (°C)

Another practical approach uses current density (J):

$$\mathrm{<span\; style="font-size:\; 16px;">A</span>}<span\; style="font-size:\; 16px;">=</span>\frac{\mathrm{<span\; style="font-size:\; 16px;">I</span>}}{\mathrm{<span\; style="font-size:\; 16px;">J</span>}}$$A = \frac{I}{J}A=JI

• J = Current density (A/mm²), typically 1–1.5 A/mm² for rigid copper busbars, or higher for Flexible Busbars with laminated layers.

4. Step-by-Step Guide to Calculate Copper Busbar Size

Step 1: Determine Maximum Load Current (I)

• Analyze the total current that the busbar will carry under maximum operating conditions.

Step 2: Select Allowable Temperature Rise (ΔT)

• Usually 30–50°C above ambient temperature for copper busbars in panels.

Step 3: Choose Current Density (J)

• Depends on busbar type:

• Solid Copper Busbar: 1–1.5 A/mm²

• Flexible Copper Busbar / Laminated Copper Busbar: 2–4 A/mm²

Step 4: Calculate Cross-Sectional Area (A)

• Apply the formula $\mathrm{<span\; style="font-size:\; 16px;">A</span>}<span\; style="font-size:\; 16px;">=</span>\mathrm{<span\; style="font-size:\; 16px;">I</span>}\mathrm{<span\; style="font-size:\; 16px;">/</span>}\mathrm{<span\; style="font-size:\; 16px;">J</span>}$A = I / JA=I/J or use thermal constant methods for precise sizing.

Step 5: Determine Busbar Dimensions (Width × Thickness)

• Choose width and thickness based on cross-sectional area and panel space constraints.

• For example, for a calculated area of 50 mm², you could choose 5 mm thickness × 10 mm width.

Step 6: Check Voltage Drop

• Ensure voltage drop is within acceptable limits, typically <1–3% of system voltage.

Step 7: Verify Mechanical and Installation Requirements

• Ensure the busbar fits within the panel or battery layout and allows proper busbar connector installation.

5. Important Considerations When Calculating Copper Busbar Size

1. Material Type: Copper vs. Aluminum – Copper has higher conductivity, so smaller cross-section can be used.

2. Busbar Type: Solid or flexible – Flexible busbars can tolerate higher current densities due to heat dissipation.

3. Insulation: Coated busbars may have slightly reduced heat dissipation.

4. Ambient Temperature: Higher temperatures require larger cross-section.

5. Future Load Growth: Consider additional margin if system expansion is expected.

6. Mechanical Strength: Thick or laminated busbars may be needed to support weight or vibration.

6. Applications of Properly Sized Copper Busbars

Copper busbars sized correctly can be used in:

• Power Distribution Panels – Efficiently distributes high current to multiple circuits.

• Battery Busbar Connections – For EV batteries, UPS systems, and renewable energy storage.

• Electrical Panels and Switchgear – Safe and low-resistance interconnections.

• Flexible Copper Busbar in Compact Designs – Ideal for EVs, battery packs, and electronics.

• High-Current Industrial Applications – For factories, transformers, and power plants.

Benefits include:

• Reduced energy loss

• Better heat management

• Reliable connections

• Space optimization in panels

Calculating the correct copper busbar size is a crucial step in designing safe, efficient, and durable electrical systems. Using formulas based on current, temperature rise, and material properties, along with careful consideration of flexible or Solid Busbar types, ensures optimal performance. Properly sized busbars enhance system reliability, reduce maintenance, and improve overall energy efficiency.

For high-performance applications, manufacturers often provide custom copper busbars, flexible copper busbar, laminated copper busbars, and busbar connectors, ensuring that each electrical system achieves maximum safety and efficiency.