Which instrument is commonly used to measure AC current without breaking the circuit?

• A. Voltmeter
• B. Ammeter with series connection
• C. Clamp-on ammeter
• D. Multimeter in resistance mode

Answer: (C)

Measuring AC current without breaking the circuit relies on magnetic coupling around a single conductor. A clamp-on ammeter uses a split-core current transformer: as AC flows, it creates a changing magnetic field that the clamp senses and converts into a current or voltage reading. Because the conductor simply passes through the clamp, the circuit stays closed and unaffected, making it ideal for testing live systems.

A voltmeter is for voltage, not current, so it won’t give a direct current reading. An ammeter in series would require opening the circuit to insert the meter, which contradicts the “without breaking the circuit” requirement. A multimeter in resistance mode measures resistance, not current in operation. So the clamp-on ammeter is the appropriate instrument for this purpose.