An ohmmeter must never be used on a circuit that may be __________.

• A. Grounded
• B. Unenergized
• C. Shorted
• D. Energized with a voltage

Answer: (D)

Measuring resistance with an ohmmeter relies on the meter's own small current flowing through the circuit to determine value. If the circuit still has voltage, that external energy can drive current into the meter, distort the reading, and potentially damage the meter or create a safety hazard. The essential rule is to de-energize and isolate the circuit before using an ohmmeter. Grounded or unenergized conditions are safe to test once power is removed, while the presence of voltage is what makes using an ohmmeter dangerous or unreliable.