Kirchhoff's current law (KCL)

This law is also called Kirchhoff's point rule, Kirchhoff's junction rule (or nodal rule), and Kirchhoff's first rule.

The principle of conservation of electric charge implies that:

At 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.

Adopting the convention that every current flowing towards the node is positive and that every current flowing away is negative (or the other way around), this principle can be stated as:

\sum_{k=1}^n {I}_k = 0

n is the total number of branches with currents flowing towards or away from the node.

This formula is also valid for complex currents:

\sum_{k=1}^n \tilde{I}_k = 0

The law is based on the conservation of charge whereby the charge (measured in coulombs) is the product of the current (in amperes) and the time (which is measured in seconds).