A short circuit is when the impedance between an energized conductor and another element in contact with it becomes low enough.

• A. Resistance
• B. Impedance
• C. Both A and B
• D. None of the above

Answer: (B)

A short circuit is a fault where the path between an energized conductor and another conductor or ground offers very little opposition to current flow. That opposition is called impedance—the total resistance to current, including both resistance and reactance. In AC circuits, impedance matters because reactance (from inductance and capacitance) affects how much current can flow; in DC, impedance simply reduces to resistance. Because the fault path presents a very small impedance, a large current can surge, limited mainly by the source’s own impedance and any protective devices. Focusing only on resistance would miss the reactive part that can be significant in many systems, so describing a short circuit in terms of impedance best captures the actual fault behavior.