Why is it important to disconnect power before using an ohmmeter?

• A. To prevent interference with existing current and potential damage to the ohmmeter or circuit
• B. To speed up measurements
• C. To calibrate the meter
• D. To heat components

Answer: (A)

An ohmmeter measures resistance by sending a small test current through the component and reading the resulting voltage. If power is applied to the circuit, that live current and voltage can interfere with the meter’s signal, giving an inaccurate reading or making the meter fight against the circuit. More importantly, introducing the meter’s test current into a powered circuit can push current into energized parts, potentially damaging the meter or the circuit and creating a safety risk. disconnecting power isolates the component, ensures the measurement reflects just its resistance, and protects both equipment and personnel.