Which instrument is used to find a circuit problem when power is removed from the circuit?

Which instrument is used to find a circuit problem when power is removed from the circuit?

• A. Voltmeter
• B. Oscilloscope
• C. Ammeter
• D. Ohmmeter

Answer: (C)

When a circuit is de-energized, you look for faults by checking resistance paths. An ohmmeter is designed for this: it injects a small current and measures resistance, letting you spot opens, shorts, or abnormal resistance between points. This approach reveals how the circuit should conduct if powered, without applying voltage or current that could conceal faults or be unsafe. Voltmeters require a live circuit to measure voltage, and oscilloscopes also monitor powered signals, making them unsuitable for path-checking with power removed. An ammeter measures current, which isn’t present or meaningful when the power is off, so it isn’t useful for locating faults in a de-energized circuit.

When a circuit is de-energized, you look for faults by checking resistance paths. An ohmmeter is designed for this: it injects a small current and measures resistance, letting you spot opens, shorts, or abnormal resistance between points. This approach reveals how the circuit should conduct if powered, without applying voltage or current that could conceal faults or be unsafe.

Voltmeters require a live circuit to measure voltage, and oscilloscopes also monitor powered signals, making them unsuitable for path-checking with power removed. An ammeter measures current, which isn’t present or meaningful when the power is off, so it isn’t useful for locating faults in a de-energized circuit.