Measuring direct current with a clamp meter is simple, fast and accurate. There is no need to disconnect the measured circuit, it is enough to wrap the measured wire with the measuring clamps, and the current value will appear on the display.  

How to proceed when choosing a suitable device?
Current measurement requirements over a wide current range can be encountered in a vehicle. From hundreds of amperes of starting currents to milliamps when finding leakage currents. However, most clamp meters are not capable of covering such a range. As for high current clamp devices, they are mostly robust devices with larger clamps, due to the possibility of measuring even on thick cables.Their best resolution is usually 0.1A or 0.01A (= 10mA). At first glance, the 10mA seems usable even for measuring small currents. However, when we take into account the permissible error defined by the manufacturer, we find that such a device is actually usable for measurements from 100mA or even more. And that is no longer enough to measure really small currents.

Figure: Example of clamp-on instruments for measuring high currents
As for the measurement of really small direct currents, there are devices available on the market with a resolution starting from 1mA. They are suitable for searching even very small subscriptions. However, the maximum range of such devices often ends at a few tens of A, so they are not suitable for measuring, for example, starting currents. Structurally, they are smaller, compact devices with smaller clamps suitable also for measurements on thin conductors.

Figure: Example of clamp-on instruments for measuring small (mA) currents
Therefore, it can be a good solution for a service technician to have two devices – one for large currents and the other for small currents.  
However, you can also find devices that meet both demanding requirements – measuring high currents up to 1000A and at the same time offering an excellent resolution of 1mA.



Figure: Example of a clamp meter for measuring currents over a wide range



Important principles when measuring current with a clamp meter:It is necessary to make sure that the pliers are well closed.It is necessary to grip only one conductor (one core) in the pliers. In the case of measurements on a multi-core cable, the result is the sum of the currents flowing through all individual conductors (taking into account the direction of current flow).Before measuring direct current, it is necessary to reset the display. The devices have a dedicated button for this (mostly marked as ZERO or REL)


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One of the areas of use of the clamp ammeter in the practice of an auto electrician is the measurement of the discharge current of the car battery.
In such cases, we recommend using a discharge current recorder LeakTest LT-10. 
Main advantages:
● There is no need to intervene in the vehicle’s electrical installation (e.g. disconnecting the car battery, etc.)
● The vehicle is properly closed and locked during the measurement
● The measurement is not limited in time, it can take place, for example, all night.
● The results are available in numerical (table) and graphic form