What is a clamp-on ammeter and what is it used for?

• A. A non-contact method to measure current by clamping around a conductor; does not require breaking the circuit.
• B. A device that clamps around a conductor to measure temperature.
• C. A device that requires the circuit to be opened to measure current.
• D. A device that measures voltage drop across a resistor.

Answer: (A)

A clamp-on ammeter measures current without opening the circuit by clamping a loop around a single conductor. The clamp contains a magnetic core that senses the magnetic field produced by the current in that conductor and converts it into a readable current value on the meter. This non-invasive method is especially useful for live circuits, so you can check loads, troubleshoot faults, or verify UPS feeders and equipment without disconnecting anything.

Other options describe different measurements or procedures that aren’t what a clamp-on ammeter does. Measuring temperature requires a heat sensor, not a current clamp. Needing to open the circuit would defeat the purpose of a clamp-on tool. Measuring the voltage drop across a resistor is what a voltmeter or multimeter in a separate function does, not a current clamp.