Measuring AC Current with Clamp Probes

AC clamps can measure the current flowing through a wire in a non-invasive way. We’ve had customers ask frequently which wire in 2 or 3-phase AC applications they should test the current from. With 2-phase power, use a clamp meter on the live (or “hot”) wire to get a good reading. (Fig. 1) Ensure your device is set for testing AC current and is set to a value (in amps) close to the current range you are testing.

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Fig. 1: Testing a single conductor for AC current.

With 3-phase power, you’ll need to sum the three separate currents coming in on the wires to get the total current used.

Note that testing individual conductors is generally the best procedure for testing clamp current because if you clamp meters on multiple wires at the same time, the current flowing back through other wires may interfere with or cancel out your reading.