To measure electrical current, you normally have to insert the meter into the circuit. In many instances, opening up wiring connections, whether live or not, is impractical and hazardous. However, to measure AC current, you can use a clamp meter. The clamp surrounds the wire and uses its magnetic field to determine the current. This is safe, quick and accurate. Modern digital clamp meters act like two meters in one: They can do standard measurements for voltage and resistance, and they can use the clamp to measure AC current.
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Things you need
- Digital clamp meter
- Household floor lamp
- Light-duty extension cord
Turn the multimeter on and set it to read AC current.
Use the clamp meter to measure the current in a household two-wire lamp cord. Turn the lamp on. Open the clamp and close it so it surrounds the lamp's power cord. Do not pinch the wire inside clamp parts that meet together. Though the lamp is on, you should be reading nearly a zero current. Since the clamp is around two conductors carrying current in opposite directions, the magnetic fields cancel out.
Prepare an extension cord by carefully separating the two parallel conductors. Separate them for a length of about one foot. Check that the copper wire is still insulated and not exposed.
Plug the extension cord into a wall outlet and connect the lamp into the extension. Turn the lamp on and close the meter's clamp around one of the extension's conductors. You should now be getting a clear current reading of between .5 and 1.5 amps. Since the clamp surrounds only one conductor, you can get an accurate reading. Whenever you're using the clamp, it must surround only a single conductor; multiple conductors will distort the reading. When you're done testing the meter, unplug the extension cord from the lamp and discard the cord.
Tips and warnings
- The clamp works for measuring AC currents only. DC currents must be measured by inserting the meter into the circuit. Check the meter's owner's manual for more information.
- Since the clamp meter is intended to be used on live electrical wires, take precautions when working around hazardous voltages. Wear rubber gloves rated for electrical work.
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