In AC circuits, what is impedance and how does it influence current flow and conductor sizing?

• A. Impedance is total opposition to current from resistance and reactance; higher impedance reduces current and affects voltage drop and ampacity needs
• B. Impedance is only resistance and has no effect on current
• C. Impedance is the same as voltage
• D. Impedance only affects DC circuits

Answer: (A)

In AC circuits, impedance is the overall opposition to current, combining resistance (which dissipates energy as heat) and reactance (from inductors and capacitors, which store and release energy). The size of the impedance, Z, determines how much current flows for a given voltage: I = V / |Z|. So, higher impedance means less current, while lower impedance means more current. This current level affects how much voltage drops along conductors and how much heat the conductor will experience (since heating relates to I^2R). That direct link to current is why impedance also influences conductor sizing: the required ampacity depends on the current the circuit will carry. If impedance reduces current, heating and voltage drop change accordingly, but you still size conductors to handle the actual operating current and worst-case conditions, considering safety and performance. In short, impedance is the combination of resistance and reactance that governs current, and that current level drives both voltage regulation and conductor sizing.