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 |
