HomeElectricalElectrical Panel Design: Busbar Size Calculation Chart PDF

Electrical Panel Design: Busbar Size Calculation Chart PDF

A busbar is a kind of copper or aluminum conductor rod, which collects Electricity from one or more circuit and distributes it. Today we will discuss the busbar size calculation chart pdf.

busbar calculation

Busbar Calculation

Busbar calculation/selection is done in two ways:

  1. Directly based on current value and
  2. Based on transformer rating

Busbar Size Calculation Chart PDF

Busbar calculation in low voltage line

Busbar calculation is mainly based on cable rating (ampere). Look at the picture. In the picture, there is a low voltage side busbar.

busbar calculation
LT side Busbar

The first way is if we know the current value or cable size:

In the above picture, there is cable size in low voltage line:

( 4 * 4 * ( 1*500 ) rm ) which means ( 1 * 500 ) rm is = 900 A.

In the picture, the circuit breaker value is, ACB = 3200 A.

For this circuit breaker ( 1 * 500 ) rm = 900 A cable has been selected. As four ( 1 * 500 )rm cable size has been taken, it means,

4 * ( 1*500 ) rm where ( 1*500 )rm = 900 A

Total Cable ( 4 ) * Cable Size ( 900 )rm

4 * 900 = 3600 A

We know, that for calculating/selecting a busbar we need to select a busbar of equal or high cable rating. There is 4000 ampere above 3600-ampere rating. So we have to calculate and select busbar for this 4000 ampere.

The second way is if we know transformer rating:

There is a transformer rating in the picture. First, we have to know the line current from transformer rating, and then multiply it with safety factor 1.25 for busbar calculation.  

Transformer Rating = 2000 KVA

Line Current = 2887 A

Safety Factor, (S.F) = 1.25

= 2887 * 1.25

= 3608 A

There is 4000 ampere above 3608-ampere rating. So we have to calculate and select busbar for this 4000 ampere.

Busbar size selection

Width and Height are specific for any busbar, but length is not fixed. We know that we have to select the busbar by multiplying Width  *  Height. That’s why we need to know Width and Height. Here is a picture of the busbar Width and Height.

The size of busbar we can find in the market

Width *  Height (W*H)(W*H) sqmm(W*H) sqmm

Generally, the busbar is calculated by formula.


1 sqr mm = 2 Amp Current (For copper)

1 mm Width * 1 mm Height = 2 Amp Current

Look at the busbar picture, let us know which part we need to know for multiplying Width * Height.

busbar calculation

Here we are seeing width and height. We have to multiply this Width * Height for busbar calculation.

Busbar calculation for 4000 ampere

We have found 4000-ampere current in both ways. We have to do a busbar calculation for 4000 amperes.

We know,

1 sqr mm = 2 Amp Current


2 Amp Current = 1 sqr mm BusBar

4000 amp Current = 4000/2

= 2000 Sqr mm BusBar

So, we need a 200 mm square busbar for a 4000-ampere current. We will select the busbar by (Width * Height) rating from the chart.

From the busbar chart,


Width = 100 mm and Height = 10 mm is taken and (Width * Height) multiply


Width * Height

= 100*10 (It can be of any size)

= 1000 sqmm

Like cable selection, a busbar is selected by adding one or more busbars together. As we are selecting a 100 square mm busbar, then we need two busbars of 100 square mm for 2000 square mm. By which we can select a 2000 square mm busbar by adding both of them. Look at the picture. There are multiple busbars of different sizes connected together.

busbar calculation

Busbar size calculation

Busbar length is selected based on the panel box size. Whatever will be the panel box size, the busbar will be of the same size. But when we have to put the busbar inside, we need to cut the busbar to reduce the size.

Busbar weight calculation

Suppose, the busbar length is 30 feet (9144mm), height 10mm, and width 100 mm [(100*100)mm^2]

We know,

Volume= Length*Height*Width

= 9144 * 10 * 100

= 9144000 mm3

= 9144000/109

=9.0144 * 10-3 m3 (in meter)


বাসবার হিসাব

= 8960 kg/m3 * 9.0144*10-3

= 81.93 kg

Busbar price calculation:

If we know the size and weight of the busbar, it is not difficult to determine the price. First, we need to look at the size if it is suitable according to its weight. We must have to calculate before buying a busbar. If the weight is similar to the size then it is quite suitable. But if it is not similar then it may have some admixture. If the size and weight are perfect then you can calculate the price by the price per kg of copper.

Suppose, per kg of copper is 800 BDT


 81.93 kg*800 BDT

= 65544 BDT

Busbar selection and calculation on the high voltage side are the same as on the low voltage side. We have to just multiply line current with safety factor 10.

busbar calculation

There is a 105-ampere line current in the picture. We have to multiply 10 with it for busbar selection and calculation.


Line current = 105 * 10

= 1050 A

We have to calculate busbar for this 1050 ampere current by using formula:

1 sqr mm = 2 Amp Current

2 Amp Current = 1 sqr mm BusBar

1050 amp Current = 1050/2

 = 525 sq mm BusBar

= 600 square mm busbar

For 1050 A we need 600 sq nmm busbar. Width * Height = 60 * 10 = 600A busbar is selected from size selection chart.  

It’s not a problem if the size is slightly high. Then the rest of the work is as same as the low voltage line. Now you can ask a question: Why we have selected a low-value busbar for the high voltage side? Because the high voltage line has less current and the busbar is selected based on busbar current. Measuring HT side busbar size and weight is as same as LT side.

That was all for today’s article: Busbar size calculation chart pdf

Hope now you understand the busbar size calculation chart pdf

If you have any queries on the busbar size calculation chart pdf, please ask in the comment section.

You can also read: What is the Substation – The Main Purpose of an Electrical Substation

Busbar Size Calculation Chart PDF Download: Electrical Panel Design.PDF

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Md. Nazmul Islam
Md. Nazmul Islam
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