How to Calculate Busbar Size & Cross-Section for Your Load Requirement

 

 

The selection of the correct busbar size and cross-section is of the utmost importance in the design of any dependable electrical distribution system. In the case of LT/HT panels, MCC/PCC panels, switch gear assemblies, EV charger power modules, and industrial distribution boards, an accurately sized busbar guarantees safe current passing, power loss is kept to the smallest possible, overheating is prevented, and in case of failure, only the least dangerous failure mode, insulation breakdown or fire hazards, is avoided.

A busbar is the heart of an electrical system. That is why an undersized busbar can lead to overheating and thus going out of service, while an oversized busbar will simply be costly and occupy more space than needed. The present guide gives you a step-by-step, intuitive, and scientifically correct approach to the busbar size calculation for both copper and aluminum.

 

This extensive guide will discuss the following topics:

• Definition and importance of busbars.

• Essential parameters necessary to know before starting the process.

• Cross-sectional area calculation.

• Ampacity mentioned in the parameters.

• Short-circuit withstand calculations.

• Examples Provided.

• Sizes Recommendation.

• Best practices of busbar design for safety and efficiency.

Let’s go back to the basics first.

 

 

 

1. What exactly is a busbar? Why does it matter to size?

A busbar is a stiff metal strip, normally comprised of:

• Copper (electrolytic grade)

• Aluminium (EC Grade / IS 5082 grade)

These strips manage the flow of electricity to different circuits or to the devices located inside power panels such as:

• Power Control Centers (PCC)

• Motor Control Centers (MCC)

• Distribution Boards

• Low Voltage (LV) and High Voltage (HV) Switchgear

• Electric Vehicle (EV) Charger Power Cabinets

• Automatic Transfer Switch (ATS) Panels

• Uninterruptible Power Supply (UPS) Panels

• Solar Inverters & ACDB/DCDB

Busbars transport large currents, hence need to be picked up correctly to make sure that:

• No temperature rise in unsafe category

• Mechanical strength for short-circuit mitigation

• Voltage drop is within acceptable limits.

• Long-term reliability and operational efficiency are proper

• Power loss and heat generation are minimized.

Miscalculation of busbar size is amongst the major reasons leading to panel failures, hot spots, burnouts, and failed FAT/SAT tests.

 

 

 

2. Key Data Required Before Calculating Busbar Size

The following design parameters must be collected before sizing the busbar:

2.1 Total Load (in kW or kVA)

This is the total connected load or the maximum demand load.

2.2 System Voltage (V)

The standard is:

• 415V (3-phase LT)

• 11kV / 33kV (HT systems)

2.3 Power Factor (PF)

Typically, it ranges from 0.80 to 0.95.

2.4 Type of Material

• Copper – superior conductivity, smaller proportion

• Aluminium – cheaper, larger size for same lost heat

2.5 Maximum Allowable Temperature Rise

According to IEC 61439:

• Copper: to 105°C insulation class

• Aluminium: a bit lower because of higher resistivity

2.6 Installation Conditions

• Ventilated or closed

• Horizontal or upright

• Covered or naked

• No space and / or cooling available

Ultimately, all these parameters affect the current carrying capacity of a busbar.

 

 

3. Current Carrying Capacity of Busbars (Ampacity)

The most significant factor in the busbar dimensioning is the current density, defined usually as:

Amps per mm² (A/mm²)

Widely accepted safe design values in the industry:

Material	Recommended Safe Density	Notes
Copper Busbars	1.2 – 1.6 A/mm²	Use 1.2 A/mm² for conservative design
Aluminium Busbars	0.8 – 1.0 A/mm²	Larger cross-section required

In extreme or high-temperature applications, choose the minimum limit of the ranges.

 

 

 

4. Busbar Cross-Sectional Area Formula

After identifying the load current (I) the following formula is applied:

Here, in this situation:

• Copper’s current density is 1.2 A/mm²

• Aluminum’s current density is in the range of 0.8–1.0 A/mm²

   

 

 

5. Busbar Sizing Method in Steps

 

And allows us to break the process down into a few simple steps. 

 

Step 1 — Determine Full Load Current (FLC)

 

If the load is specified in kW: 

 

 

If the load is given in kVA: 

 

 

 

 

Step 2 — Select Material (Cu or Al) 

 

Copper has the advantage of being the more conductor, but aluminum is the more affordable metal. 

 

 

Step 3 — Pick Current Density (A/mm²) 

 

For a more conservative design: 

• Copper: 1.2 A/mm² 

• Aluminum: 0.8 A/mm² 

   

 

Step 4 — Compute the Required Cross-Section 

 

Use the following for the calculation of cross-section: 

 

 

Step 5 — Choose Standard Busbar Size 

 

Select from the standard sizes used in the industry: 

• 25×5 (125 mm²) 

• 32×6 (192 mm²) 

• 40×6 (240 mm²) 

• 40×10 (400 mm²) 

• 50×10 (500 mm²) 

• 80×10 (800 mm²) 

• 100×10 (1000 mm²) 

   

 

Step 6 — If a Larger Area is Required, Busbars in Parallel 

 

Suppose: 

2 bars of 50×10 = 1000 mm² 

3 bars of 80×10 = 2400 mm² 

The parallel busbars increase the cooling effect and the resistive heating gets reduced. 

 

 

Step 7 — Confirm Short-Circuit Strength and Temperature Rise 

 

Thus, it becomes a critical point where safety and compliance with IEC 61439 standard go hand in hand.

 

 

 

 

6. Detailed Practical Busbar Sizing Examples

Let us now take a closer look at some real industrial scenarios in an exhaustive manner.

 

Example 1 — Busbar Sizing for 250 kW Load

Supposed:

•          Load = 250 kW

•          Voltage = 415V

•          PF = 0.9

•          Material = Copper

Step 1: Calculate current 

I is found to be near 387A.

Step 2: Area Requirement

≈ 323 mm²

Step 3: The Last Option

Types accessible:

• 40×8 = 320 mm²

• 32×10 = 320 mm²

Either size’s selection is correct.

 

Example 2 — 1000A Copper Busbar System

≈ 833 mm²

A number of options to select from:

• 50×16 = 800 mm² (slightly less)

• 50×10 × 2 bars = 1000 mm² (secure & with better cooling)

The parallel design will always be the most favored option for high-current installations like PCC panels.

 

Example 3 — 1600A Aluminium Busbar

= 2000 mm²

Options:

• 2 × (100×10) = 2000 mm²

• 3 × (80×10) = 2400 mm² (safer)

Larger cross-sections are commonplace in aluminum systems.

 

 

7. Short-Circuit Withstand Capacity (Mechanical Strength)

In the event of a fault, busbars need to withstand enormous magnetic forces that are generated in a matter of milliseconds.

Force per meter:

 

 

Where:

• I = Short-circuit current (kA)

• L = Distance between busbars

• S = Spacing factor

For normal LT panels (36-50 kA fault level), the supports must be subjected to the following tests:

• Thermal withstand (1 sec rating)

• Dynamic withstand (peak kA rating)

The use of DMC/SMC/GPO-3 supports guarantees strength and safety.

 

 

8. Derating Factors That Reduce Busbar Ampacity

The actual carrying capacity of the busbars is lower than the theoretical capacity, which is due to the practical factors prevailing in the environment:

8.1 Ambient Temperature

The rise in ambient temperature → decrease in ampacity.

8.2 Enclosed Panels / Poor Ventilation

The heat cannot escape; derating is necessary.

8.3 Vertical Mounting

The heat naturally goes up → vertical strips need to be derated.

8.4 Insulated or Sleeved Busbars

The busbar temperature is higher due to the sleeves; derate it by 10–20%.

(This point concerns the busbars of EV chargers, of MCB/mixed copper busbars, and of sleeved aluminum busbars in particular.)

8.5 Surface Plating

Tin/nickel plating marginally increases surface resistance but at the same time offers protection against corrosion.

 

 

 

9. Recommended Busbar Sizes (Quick Industrial Reference)

Current (A)	Copper Busbar Size (mm)	Aluminium Busbar Size (mm)
200A	32×6	40×6
400A	40×10	50×10
630A	50×12	80×10
800A	50×15	80×12
1000A	2 × (50×10)	2 × (60×10)
1250A	2 × (63×10)	2 × (80×10)
1600A	2 × (80×10)	2 × (100×10)
2000A	3 × (80×10)	3 × (100×10)
2500A	3 × (100×10)	4 × (100×10)
3200A	4 × (100×10)	4 × (125×10)
4000A	5 × (100×10)	5 × (125×10)

These are widely used by panel builders across India. Always check compliance with IEC standards.

 

 

 

 

10. Copper vs Aluminum Busbars — Which One Is The Best?

 

Both of these materials are often used in various applications depending on the cost. 

Copper Busbars

• Conductivity higher than aluminium (58 MS/m)

• Compact & efficient

• Lower temperature increase

• Perfect for switchgear, PCC panels, EV fast chargers, critical power systems

• Styles: tinned copper, silver-plated copper, or uncoated

 

Aluminium Busbars

• Most favorable due to light weight and low cost

• Capable of handling big power distribution

• Great in solar, industrial, utility, and non-corrosive environments

• Styles: plain aluminium, sleeved aluminium, plated aluminium

 

When to use Copper?

• High current densities

• Compact panel layouts

• Corrosive/coastal environment

• EV charging infrastructure

• Data centres & critical loads

 

When to Use Aluminium?

• Cost-sensitive projects

• Large cross-sectional requirements

• High-voltage applications

• Solar utility-scale installations

   

   

 

 

11. Advanced Considerations in Busbar Sizing

 

 

11.1 Skin Effect at Higher Frequencies

In AC systems, current is flowing mostly on the surface.

Instead of using a single thick bar, use several thinner bars.

 

11.2 Proximity Effect

Phases that are close to each other have an effect on current distribution.

Arrange the wires so that the heat generated is the least possible.

 

11.3 Neutral Busbar Sizing

Usually sized at:

• 50% of phase for balanced industrial loads

• 100% of phase for harmonic loads (IT systems, UPS loads)

 

11.4 Earthing Busbar

Copper or GI busbar is sized to be able to manage fault and leakage currents (the same or even slightly lower than for the phase).

 

 

 

12. Common Mistakes in Busbar Sizing

These costly errors should be avoided:

• The wrong current density is being used.

• Temperature rise tests are ignored.

• Thick single bars are chosen rather than several strips.

• Misjudged spacing results in short-circuit failure.

• Environmental conditions are not taken into account.

• Heat rise in aluminum is underrated.

• Mixing different metals without doing proper plating (causes corrosion).

Proper busbar sizing guarantees long-term reliability, lower maintenance costs, and safe operation.

 

Conclusion

The selection of the busbar size and cross-section accurately is the foundation upon which the electrical panel’s safety and robustness will rest. By demystifying the factors of load current, current density, material selection, short-circuit strength, and derating, the panel makers and the engineers will certainly select the right busbar whether copper or aluminium.

It does not matter if your application is a switchgear panel, MCC/PCC, solar plant, EV charger, or industrial automation system, the right-sized busbars will provide:

• Peak performance

• Heat management

• Strength

• Extended lifetime

In case of doubt, always take the higher safety margins. It is a rule that in electrical systems, safety and reliability must not be sacrificed.

 

Need Premium Quality Busbars in India?

In case you are looking for well-designed copper or aluminium busbars, tinned copper busbars, sleeved aluminium busbars, fabricated switchgear busbars, EV charger busbars, or custom busbar assemblies — Adinath Enterprises is a reliable producer and supplier.

With great craftsmanship, plating quality, and dimensional precision, we supply high-quality, IS/IEC-compliant busbars all over India.

Visit us to see our entire product range: adinathenterprises.com