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

• A. Clamp-on type ammeter
• B. Voltmeter
• C. Ohmmeter
• D. Wattmeter

Answer: (A)

A clamp-on ammeter is used to measure current without breaking the circuit. Its jaw clamps around a single conductor and senses the magnetic field produced by the current flowing through that conductor (often via a current transformer or Hall-effect sensor). The device then converts that magnetic signal into a current reading, all without opening the circuit path. This lets you measure live current safely and conveniently.

In contrast, a voltmeter is connected across two points to measure voltage and doesn’t measure current directly. An ohmmeter measures resistance by applying a small current through a component, which requires the circuit to be de-energized and the component isolated. A wattmeter measures power (the product of voltage and current) and isn’t used to measure current directly in a way that avoids altering the circuit.