How to Select Busbar Size

Selecting the correct busbar size is a critical step in designing a safe, efficient, and reliable electrical system. Whether used in power distribution panels, EV battery systems, switchgear, or industrial equipment, proper busbar sizing directly affects current carrying capacity, temperature rise, electrical resistance, and system lifespan.

This article explains how to select busbar size step by step, covering key factors, calculation principles, material choices, and practical engineering considerations for B2B and industrial applications.

What Does “Busbar Size” Mean?

Busbar size typically refers to the cross-sectional dimensions of a busbar, including:

• Width

• Thickness

• Cross-sectional area (mm²)

The busbar size determines how much current it can safely carry while maintaining acceptable temperature rise and low electrical resistance.

Why Proper Busbar Size Selection Is Important

Incorrect busbar sizing can result in:

• Overheating and insulation failure

• Excessive power loss due to high resistance

• Voltage drop and unstable system performance

• Reduced equipment lifespan or safety risks

Correct busbar size selection ensures:

• Safe current transmission

• Low resistance and high efficiency

• Compliance with IEC and UL standards

• Long-term system reliability

Key Factors to Consider When Selecting Busbar Size

1. Rated Current (Current Carrying Capacity)

The maximum continuous current is the primary factor when selecting busbar size.

A commonly used engineering guideline is current density:

• Copper Busbar: 1.2 – 1.6 A/mm²

• Aluminum Busbar: 0.8 – 1.2 A/mm²

Basic calculation formula:

Busbar cross-sectional area (mm²) = Rated current (A) ÷ Current density (A/mm²)

This provides an initial reference, which must be adjusted based on temperature rise and installation conditions.

2. Busbar Material Selection

Copper Busbar

• High electrical conductivity

• Lower resistance

• Smaller size for the same current

• Ideal for high-current and compact systems

Aluminum Busbar

• Lightweight and cost-effective

• Requires larger cross-section

• Higher resistance compared to copper

For most high current busbar applications, copper is the preferred choice.

3. Allowable Temperature Rise

Busbar size must ensure that temperature rise stays within acceptable limits:

• Typically ≤30°C for switchgear

• Up to 50°C in certain enclosed environments

Higher allowable temperature rise requires:

• Larger busbar size

• Improved ventilation

• Laminated busbar or insulated busbar designs

4. Installation Environment and Cooling Conditions

Cooling conditions significantly affect busbar sizing:

• Open air installation → smaller busbar size

• Enclosed cabinet → larger cross-sectional area

• Forced air cooling → increased current capacity

• Laminated busbars → improved heat dissipation

Environmental factors such as ambient temperature and enclosure design must be considered.

5. Electrical Resistance and Voltage Drop

Busbar resistance increases with length and decreases with cross-sectional area.

In applications such as:

• Battery energy storage systems

• EV battery packs

• DC power distribution

low resistance is critical to reduce voltage drop and power loss, making correct busbar sizing essential.

6. Short-Circuit Withstand Requirements

In power distribution systems, busbars must withstand short-circuit currents without mechanical deformation.

Factors influencing this include:

• Busbar thickness

• Mechanical strength

• Support spacing

• Short-circuit current level (kA) and duration

Oversizing the busbar improves short-circuit performance and system safety.

Typical Copper Busbar Size Reference

Note: Actual busbar size selection should be verified based on standards, temperature rise, and installation conditions.

Laminated Busbars and Size Optimization

Using laminated busbars allows engineers to reduce overall busbar size while maintaining high current capacity.

Advantages include:

• Lower inductance

• Reduced resistance

• Better thermal performance

• Compact and lightweight design

Laminated busbars are widely used in:

• EV power electronics

• Inverters and converters

• UPS systems

• High-frequency switching applications

Applications Requiring Accurate Busbar Size Selection

• Electrical switchgear and control panels

• Power distribution systems

• EV and hybrid vehicle battery systems

• Renewable energy inverters

• Industrial automation equipment

• High-current DC systems

FAQ: How to Select Busbar Size

Q1: Can I oversize a busbar?
Yes. Oversizing reduces temperature rise and resistance but increases cost and space requirements.

Q2: Is copper always better than aluminum?
Copper offers better conductivity and compact design, while aluminum is chosen for cost and weight advantages.

Q3: Do laminated busbars allow smaller sizes?
Yes. Laminated busbars improve electrical and thermal efficiency, enabling compact designs.

Q4: Are there standards for busbar size selection?
Yes. Common references include IEC 61439, UL 508A, and IEEE guidelines.