How to Size a Busbar (Busbar Size Calculation)

Why accurate busbar sizing is required?

While selecting busbar one should keep in mind the application, current carrying capacity and budget as under sized busbar can cause heating and damage in bus bar while over sized busbar can affect the cost of project.

 

Types of busbar

On the basis of material, busbar is of five types:

 

Material	Current carrying capacity per mm2	Application
Copper	1.2 Amp/mm2	Panels and board
Aluminum	0.8 Amp/mm2	Panels and board
Galvanized steel	0.6 Amp/mm2	Electrical earthing
Iron steel	0.6 Amp/mm2	Trolleys, unloader & traction
Silver steel	1.6 Amp/mm2	Rarely used due to high cost

 

 

AC & DC busbar: 

There is no difference in a DC and AC busbar. For example: a busbar with 200 Amp current carrying capacity be either used for carrying AC or DC 200 Amp current.

 

What is safety factor (S.F)? 

It is a common practice to size a busbar with the consideration of future load expansion. For this reason, we consider some safety factor while busbar sizing. Normally, safety factor is taken as 25% of the load.

 

Standard bus bar size: 

S.Nos. Standard bus bar size

 

• 20*5 mm
• 20*10 mm
• 30*10 mm
• 40*10 mm
• 80*10 mm
• 100*10 mm
• 125*10 mm

 

Busbar sizing calculator parameter: 

• Choose the method: provide load (in kVA) and busbar size
• If load selected: rated current of equipment and required safety factor (S.F) to be entered o For option: option for DC, 1-phase AC and 3-phase AC. o For DC circuits: voltage (in volts), power (in kW) and safety factor

(S.F) (in percentage) are required o For AC circuits: voltage (in volts), power (in kVA), and safety factor (S.F) are required.

• If busbar size selected: width and thickness of busbar to be provided in mm.

 

Steps for busbar sizing calculation:

The formula for current carrying capacity of a busbar, when busbar size is given:

 

For copper busbar:      Iccc = 1.2*busbar width*bus bar thickness

For silver steel busbar:  Iccc = 1.6*busbar width*bus bar thickness

For aluminum busbar:  Iccc = 0.8*busbar width*bus bar thickness

For iron busbar:   Iccc = 0.6*busbar width*bus bar thickness

For galvanized steel busbar:  Iccc = 0.6*busbar width*bus bar thickness

 

Solved Example:

When busbar size is given:

Consider a busbar whose width and thickness are given in mm

Given:

Width = 100 mm

Thickness = 10 mm Safety factor (S.F) = 25%

Required:

Current carrying capacity=Iccc =? (Amps) (Amps)

 Solution:

 

Busbar type	Solution	Answer
Copper	Iccc = 1.2*100*10	Iccc =  1200 Amps
Silver steel	Iccc = 1.6*100*10	Iccc =   1600 Amps
Aluminum	Iccc = 0.8*100*10	Iccc = 800 Amps
Iron	Iccc = 0.6*100*10	Iccc = 600 Amps
Galvanized steel	Iccc =0.6*100*10	Iccc = 600 Amps

 

For single phase system: 

Consider a single phase AC system that has the following data:

Given:

Voltage =230 V

Power (S)= 200 kVA Safety factor (S.F) =25% Required:

Busbar size= Area=? (mm2) Solution:

From single phase AC circuit formula

Iccc =  200 * 1000/230 * (1+25/100)

Iccc = 1086.95 Amps~ 1087Amps

 

 

Busbar type	Solution	Answer
Copper	Area=1087/1.2	Area=908 mm2
Silver steel	Area=1087/1.6	Area=680 mm2
Aluminum	Area=1087/0.8	Area= 1359 mm2
Iron	Area=1087/0.6	Area=1812 mm2

 

 

For 3 phase system: 

Consider a three-phase system that has the following data:

Given:

Voltage (line to line) =480 V

Power= 400 kVA Safety factor (S.F) =25% Required:

Busbar size= Area=? (mm2)

Solution:

From three phase AC circuit formula:

Iccc =  400 * 1000/480 * (1+25/100)

Iccc = 602 Amps

 

Busbar type	Solution	Answer
Copper	Area=602/1.2	Area=502 mm2
Silver steel	Area=602/1.6	Area=376 mm2
Aluminum	Area=602/0.8	Area= 752 mm2
Iron	Area=602/0.6	Area=1003 mm2
Galvanized steel	Area=602/0.6	Area=1003 mm2