When should an ohmmeter never be connected?

An ohmmeter is designed to measure resistance in a circuit by passing a small known current through the circuit and measuring the voltage drop. However, this measurement process requires the circuit to be unpowered for accurate results and to prevent damage to both the measuring device and the circuit components.

Connecting an ohmmeter to a live circuit or a charged capacitor is highly discouraged because doing so can produce unpredictable results and potentially harm the ohmmeter. The presence of voltage can create a situation where the ohmmeter may provide erroneous readings or result in internal damage to the meter as it tries to measure resistance in a scenario that involves external current flow. In addition, current flowing from the meter into a live circuit can create dangerous conditions, including shocks or circuit failures.

The option addressing the connection of an ohmmeter to a powered circuit underscores the importance of safety and accuracy in measurements within electrical work. It is vital to ensure that the circuit is completely de-energized and any capacitors have been properly discharged before making resistance measurements. This practice is critical for both the accuracy of testing and safety while performing electrical diagnostics.