What does total impedance measure in an electrical circuit?

• A. Total impedance
• B. Equipment short-circuit current ratings
• C. Overcurrent protective devices
• D. Installation Readiness

Answer: (A)

In an AC circuit, total impedance is the overall opposition to current flow. It combines resistance (the real part that dissipates energy) and reactance (the imaginary part from inductors and capacitors, which depends on frequency). The total impedance, Z, determines how much current a given voltage will drive, following I = V / Z. At DC, reactance drops out and impedance equals resistance, since capacitors and inductors don’t oppose steady current in the same way.

This question is asking what the measure refers to in a circuit, and that is the overall opposition to current. It is not about how much current a piece of equipment can safely handle during a short circuit (that’s a short-circuit current rating), nor about overcurrent protective devices (fuses, breakers), nor about whether the installation is ready. So the measure described is total impedance.