Voltage drop can be measured

• A. When the circuit is energized only
• B. When the circuit is operating
• C. Only with power off
• D. With a resistance tester

Answer: (B)

Voltage drop is the difference in electrical potential that occurs when current flows through a component or conductor due to its resistance. You observe this drop only when the circuit is live and under load, because the current flowing through the resistance is what creates the drop. Measuring while the circuit is operating gives you the real operating condition, showing how much voltage each part of the circuit consumes or loses. If power is off, there’s little or no current, so the voltage drop across that element is essentially zero and the reading wouldn’t reflect actual service conditions. A resistance tester is not used for this purpose, since it measures resistance with the circuit isolated, not the voltage drop under load.