2026 Aircraft Electrical Systems Practice Test – Complete Exam Prep

Impedance is the opposition to alternating current in a circuit, made up of resistance and reactance. In AC, current is determined by I = V / Z, where Z = R + jX. The reactance comes from inductance and capacitance in conductors, components, and sources, and it changes with frequency.

In aircraft wiring, a fault creates a path of lower impedance, so the fault current is roughly the fault-voltage divided by the circuit’s impedance. The higher the impedance, the smaller the fault current. That reduction in fault current influences protection timing (how quickly breakers or fuses respond) and the amount of voltage drop along the wiring during fault conditions. So impedance isn’t just resistance; it’s the combined effect of resistance and reactance that limits fault current and shapes protection behavior and voltage performance in the system.