How to Use a Clamp-on Ammeter

Testing electrical alternating current (AC) circuits with a clamp on ammeter is an efficient way for troubleshooting load problems.

You will need to know the current draw of the device you are testing so you can interpret the reading. Most electrical devices will have this current draw listed on the identification tag of the device. By following a basic procedure you test any AC device with a clamp on ammeter.

Gain access to the power wire that is feeding current to the electrical device. Generally this will be in the circuit breaker panel or the device's electrical wire make up box.

Turn the meter on, if a digital type ammeter, and set the range of the meter in the area of the identification tag that is on the device. In other words if the device is suppose to draw 10 amperes of current during normal operation, you will want to set the meter in that range of reading the current draw. Most meters may have multiple range settings for the ammeter.

Open the clamp by depressing the thumb trigger on the side of the ammeter. This will open the "jaws" of the hand held meter.

Place the "jaws" around the wire and close the clamp. The clamp must be fully closed, properly seated, in order to receive an accurate reading from the power conducting wire. Allow a few seconds for the meter to register the amperage reading on the display.

Test the other wires that are feeding the device if there are multiple feed wires such as a 220 VAC, two wire, or a three-phase, three wire power circuit. All of the power wires, if multiple feeds are used, should be close in the amperage reading to each other.

Remove the clamp on meter from the circuit when finished and shut the meter off so as not to wear down the battery if a LED display is used. Some meters may have an automatic shutoff to conserve battery power.

Things You Will Need

  • Clamp on ammeter
  • Device's current load rating


  • Only AC circuits can be tested with a clamp on type ammeter.