Red Seal Electrician Practice
Meters and troubleshootingQuestion 623 of 1506

Why must resistance be measured only on a de-energized component?

  1. The meter needs the circuit voltage to power its display.
  2. The resistance of a part is always zero when it is energized.
  3. The test leads melt when current flows through the part.
  4. Other voltage in the loop gives false readings and may harm the meter.
Show answer

Correct answer: Other voltage in the loop gives false readings and may harm the meter.

In resistance mode the meter uses its own small battery. An outside voltage adds to or opposes it.

Source: Lessons in Electric Circuits I: DC (Kuphaldt), 3.9: Safe Meter Usage

Practice meters and troubleshooting

Questions last reviewed: 18 October 2026