A clamp meter is the name given to an electrical test tool that is able to combine a current sensor with a basic digital multimeter. Current is measured by clamps, while voltage is measured by probes.
The use of a hinged jaw that has been integrated into an electrical meter enables technicians to have the jaws clamped around a conductor such as a cable or wire anywhere within an electrical system so that the current in that circuit can be measured without having to disconnect or de-energise it.
While clamp meters were created just as a single purpose testing tool, modern versions offer a wider array of measurement functions, higher accuracy and in some instances even specialised measurement features. Modern clamp meters feature the majority of basic digital multimeter features including continuity, resistance and voltage measurement.
How to use a clamp meter
There are a number of steps that need to be taken in order to measure ac or dc current with the use of the jaws of a clamp meter.
The first steps to take pre-measurement are to have the test probes disconnected from the meter and ensure that fingers remain behind the tactile barrier that is on the face of the meter.
You can then turn the dial to the correct function, whether that is A ac or A dc. The jaws icon should be visible in the display, which indicates that the measurement is being carried out by the jaw.
When the current being measured is < 0.5 A, the display icon’s centre dot will be flashing, but when the current is > 0.5 A, it should be steady.
If you have equipment that is capable of measuring dc currents, then before you do so you should wait until the display has stabilised and then hit the Zero button to make sure you receive accurate readings. Doing this removes the dc offset from the meter’s reading but this can only work when the dial has been set in the right position to take dc current measurements. Before you Zero the meter the jaws should be closed with no conductor inside of them.
The next step is to press the level to release the jaws, open them and place a conductor inside them to be measured. The jaws can then be closed and the conductor centred with the use of the jaws’ alignment markings. You will then be able to see the display readings.
How to avoid electric shocks
There are also some pre-measurement steps that can be taken to avoid personal injury or electric shock.
The flexible probe should not be applied around or removed from live conductors which are hazardous by nature. Special care should be taken while fitting and removing the flexible probe.
The installation under testing should be de-energised or at the very least suitable protecting clothing should be worn during the test.
Clamp meters have become very popular due to both their convenience and their safety.