Which of the following instruments should not be used on a live circuit?

Which of the following instruments should not be used on a live circuit?

• A. Voltmeter
• B. Ohmmeter
• C. Ammeter
• D. Clamp meter

Answer: (B)

The ohmmeter is designed specifically to measure resistance and operates on the principle of applying a low voltage to the circuit to determine the resistance. When using an ohmmeter, it is essential that the circuit being tested is de-energized or not live. This is because applying the ohmmeter to a live circuit can damage the instrument and lead to inaccurate readings or potentially hazardous situations, as the internal battery of the ohmmeter can generate a voltage which may conflict with any existing voltage in the live circuit.

In contrast, instruments like voltmeters, ammeters, and clamp meters can be used on live circuits as they are specifically designed to measure voltage or current without requiring interruption of the circuit. Voltameters measure the voltage across an electrical component, ammeters measure the current flowing through a conductor, and clamp meters can measure current without directly connecting to the circuit, making them suitable for live circuits.

Understanding the correct application of these tools is critical for safe electrical work and accurate measurements.