Kirchhoff's Junction Rule

Kirchhoff's junction rule states that the total current entering a junction equals the total current leaving it. It follows from conservation of electric charge.

Equation and sign convention

• Choose entering currents as positive and leaving currents as negative, or use the opposite convention consistently.
• Label every branch current before writing the equation.
• A negative calculated current means the real direction is opposite to the assumed arrow.
• Write one independent junction equation for each required node.

Quick solved example

Currents 5 A and 2 A enter a junction. Current I and 1 A leave it.