Nodella

Meet Nodella, a wire junction where every bit of current coming in has to go out again.

Electric charge is conserved, and in a steady circuit it does not pile up anywhere. So at any junction, or node, the total current flowing in equals the total flowing out. Gustav Kirchhoff stated this current law in 1845, together with a voltage law for loops. They are the basic rules of circuit analysis.

Example: 3 amperes flowing into a node that splits into two branches might divide into 2 A and 1 A, but the two must add to 3 A. How it splits depends on the branches' resistances: more current takes the easier path.

Every circuit simulator and every electrician's calculation uses this rule. It explains why adding appliances in parallel adds to the total current drawn from the supply, and why the main fuse must handle the sum of all the branches.

The law holds for steady currents and for circuits small compared with the wavelength of their signals. At very high frequencies, charge can build up on components, and a more careful treatment is needed.