When should an ohmmeter be used?

An ohmmeter is designed to measure resistance in an electrical circuit and should be used when the power is off in the circuit. This is essential because applying power to a circuit while using an ohmmeter can lead to inaccurate readings as well as potential damage to the ohmmeter itself or the components in the circuit.

When testing resistance, the ohmmeter sends a small current through the component or circuit being tested to measure how much resistance is present. If the power were on, it could interfere with the readings and present safety hazards. Therefore, using an ohmmeter with the power off ensures a safe environment and accurate measurements of resistance.

In contrast, testing for current flow or measuring voltage requires the circuit to be powered on, which would be inappropriate and harmful when using an ohmmeter.