A clamp meter is an electrical tester that combines a voltmeter with a clamp-type current meter. It is used by electricians to measure electrical energy. Voltage is measured by attaching a set of test leads and probes, which make contact with an electrical source, such as a household electrical outlet. Alternatively, when you clamp the instrument’s jaws around a conductor carrying AC current, that current is coupled through the jaws and a reading can be obtained in a non-contact way.