How should you measure resistance with a multimeter to ensure safety?

• A. Power off, isolate the component if possible, and measure across it with the meter set to ohms.
• B. Power on and measure resistance with the meter in volts.
• C. Disconnect the meter and guess.
• D. Short the component and measure current.

Answer: (A)

Safety and proper technique when measuring resistance with a multimeter hinges on removing power and isolating the component so you read only that part’s opposition to current. To do this correctly, first power down the circuit and disconnect or lift at least one lead so the component isn’t in circuit. Then set the meter to the ohms range and place the probes across the component’s two terminals. The meter will push a tiny current through the component and display the resistance; with power off, the reading reflects only the component itself and isn’t influenced by other parts of the circuit. This also protects you and the meter from damage caused by live voltage.

Why the other approaches aren’t appropriate: measuring with power on won’t give a true resistance and can be dangerous, attempting to measure current by shorting the circuit is unsafe, and guessing won’t yield a meaningful resistance value.