Circuits and conductors
Kirchhoff: current balance
- where
- currents entering the junction (A)
- currents leaving the junction (A)
Explain this equation
Finds a missing current at a junction from the total coming in and the known currents going out. Useful for tracing branch currents at a distribution point.
ΣIᵢₙ is the sum of all currents flowing into the junction. ΣIₒᵤₜ is the sum of all currents flowing out. The calculator subtracts the known outgoing currents from the total incoming to give the missing outgoing one.
Charge does not pile up at a junction in a steady circuit, so whatever flows in must flow out. Current is not used up by loads.
Sense check: 10 A in with 6 A known out leaves 4 A in the missing branch. A negative answer means the missing current is actually flowing in, not out.
Watch out: decide arrow directions first and stick to them for every branch.
A junction does not continually accumulate charge in an ordinary steady circuit. Total current entering therefore equals total current leaving.
Draw arrows and label known branch currents. Subtract known outgoing currents from the total to find a missing branch.
Enter your values to see the result.
Common mistake
Saying current is used up by a component.
Limits
Steady currents; directions must be assigned consistently.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.