BUSBAR SIZE CALCULATOR
Electrical power system consists of multiple incoming and outgoing feeder connection, for this electrical connection busbars are required. Busbar is simply a node (conductor or group of conductors) which collects power from incoming feeder and distribute it to outgoing feeders. A busbar size is defined according to its material and current carrying capacity.
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Why accurate busbar sizing is required?
While selecting busbar one should keep in mind the application, current carrying capacity and budget as under size busbar can cause heating and damage in bus bar while over size 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 |
| 1 | 20*6 mm |
| 2 | 20*10 mm |
| 3 | 30*10 mm |
| 4 | 40*10 mm |
| 5 | 63*10 mm |
| 6 | 80*10 mm |
| 7 | 100*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
- For option: option for DC, 1-phase AC and 3-phase AC.
- For DC circuits: voltage (in volts), power (in kW) and safety factor (S.F) (in percentage) are required
- 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 calculator:
When busbar size is given:
The formula for current carrying capacity of a busbar, when busbar size is given:
For copper busbar:
For silver steel busbar:
For aluminum busbar:
For iron busbar:
For galvanized steel busbar:
When load is given:
For DC circuit:
The formula for DC circuits is given below.
For 1 phase AC circuit:
The formula for single phase AC circuit is same as DC with an addition of power factor (p.f) which is given as:
For 3 phase AC circuits:
The formula for three phase AC circuit is same as two phase AC circuit but instead of 2 we use square root 3 (~1.73) when voltage is expressed in terms of line to line (Vll) which is given as:
When voltage is expressed in terms of line to neutral then we use 3 instead of 1.73.
| Type Of Busbar | Formula |
| Copper | Area=Iccc/1.2 |
| Silver steel | Area=Iccc/1.6 |
| Aluminum | Area=Iccc/0.8 |
| Iron | Area=Iccc/0.6 |
| Galvanized steel | Area=Iccc/0.6 |
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 | ccc=0.6*100*10 | Iccc=600 Amps |
| Galvanized steel | Iccc=0.6*100*10 | Iccc=600 Amps |
When load is given:
For a DC system:
Consider a DC system that has the following data:
Given:
Voltage =230 V
Power= 20 KW
Safety factor (S.F) =25%
Required:
Busbar size= Area =? (mm2)
Solution:
From DC circuit formula
| Busbar type | Solution | Answer |
| Copper | Area=108/1.2 | Area=90 mm2 |
| Silver steel | Area=108/1.6 | Area=67.5 mm2 |
| Aluminum | Area=108/0.8 | Area= 135 mm2 |
| Iron | Area=108/0.6 | Area=180 mm2 |
| Galvanized steel | Area=108/0.6 | Area=180 mm2 |
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
| 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 |
| Galvanized steel | 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:
If we change voltage from line to line to line to neutral, for example: V (line to neutral) =277.13 V
Then we will be calculating it using formula of 3 phase AC circuit when voltage is given as line to neutral that is:
| 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 |
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