Kirchhoff's Current Law really Works to Design an Economic Busbar Trunking System!!

Kirchhoff's Current Law

This law states that, for any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node; or equivalently:

The algebraic sum of currents in a network of conductors meeting at a point is zero.

The current entering any junction is equal to the current leaving that junction. 

          i2 + i3 = i1 + i4

KCL in BBT

Once the trunking system layout is established, it is possible to calculate the absorbed current I_n on the distribution line. And line current, I_n is equal to the sum of absorbed currents. That is; 

                                               

                                                 In = Σ IB.

Example

In the above line diagram, a simple BBT layout has been shown (not in scale). After calculating the load, it is defined as the main busbar line capacity is 2000A. So after first load point or first junction point (in BBT language it is called Tap off Point), it is allowable to reduce the main line to 1000A rather than the whole BBT line to 2000A. In this way, the economical busbar trunking system has been designed. That means junction point one, the entering current will be equal to the leaving current. 


In conclusion, in a BBT System, the ampere rating selection of a BBT will be the sum of the current drawn by its distribution side. If a line of BBT starts with an ampere rating, then it is possible to reduce in a lower rating depending on the load in the rest of the distribution line.